Cliff's Quadrajet Parts and Rebuild Kits
Quadrajet Problem Solving => Dialing in your rebuilt Quadrajet carburetor => Topic started by: bob69 on January 30, 2022, 03:49:24 PM
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I need help fine tuning my Q-jet. I'm working on a 07029207 1074 SR crab. I have Cliff's book and have been following recipe number two for my application:
1) 1969 Camaro, 350 sbc, 200r4 trans, 1800 stall, 3.55 axle, 9 btdc.
2) Cam. 214 int / 224 exh at .050, .444 int / .446 exh, 112 lsa.
3) summit 152123 heads, 165 cc int runner, 72 ccv, 2.02 int / 1.60 exh. Flat top pistons.
The carbs idle was very rough. After several adjustments, with no success, I hooked up a A/F ratio tester. The idle A/F came in at high 15s to low 16s. Too lean. However, the A/F at steady state running (2000 rpm) was a very nice 14.6 to 15.0.
I increased the jets two sizes. The idle improvement was significant. The car now idles very smoothly at 650 rpm. The throttle screw was turned down by over a full turn. Idle screws now have adjustability when they did not before. Pretty sure closing the transfer slots is why.
The idle A/F changed to around 14.1. However, steady state running (2000 rpm) changed to low 13's. Way too rich for normal driving.
The cards spec's are:
Jet. 71 (was 69)
Rod. 37 (was 36)
Idle tube .039
Idle dcr. .053
Upper IAB .081. *
Lower IAB .063
Upper MAB .070. (was .050)
Lower MAB .070. (was .050)
IAB. .098. (was .093)
Idle discrage .095
Secondary. AN
I think the UIAB is too large. I would like to decrease it to something closer to what Cliff suggest. Any suggestions how much. The jets should also be dressed. How much? I would like to get idle around 14.1 A/F and steady state around 14.7 to15.0 A/F. I prefer to keep the UIAB in the body and not use the air horn air bleeds.
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I believe 7029207 Original jets were 66. Increasing jet size would not have fixed your idle. You have missed something. The original setup of this carb ( before modifications ) would have been closer. If the original setup was still stock ( not modified )
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We don't change main jets to tune idle fuel. You may see a superficial improvement there simply because all the fuel to the idle tubes has to go past the jets, but this is not how idle tuning is accomplished. Trying to add fuel by changing the jet/rod relationship throws a monkey wrench into the rest of the tune as you are finding out.
Several things to mention. You are working with a factory "high performance" carburetor. Most likely it is a Service Replacement not an original 1969 unit.
The originals and SR's are not set up the same internally.
Either way both as a relatively "generous" idle system and support engines with big cams in them without needing much done to them. The originals have more idle fuel to the mixture screws than the SR's if anyone is taking notes.
Since you opened up the Main Airbleeds then the stock jets and metering rods are out the window. You will need larger metering rods to lean it back down since you moved up to 71 main jets.
I would recommend removing the APT screw in the baseplate and getting one of my external/adjustable ones. This will save having to take the carb back apart for fine tuning part throttle A/F.
Second I would quit chasing the A/F meter and tune for best results instead. You shouldn't have had to touch the idle system in the first place assuming your 350 engine build has over 10 to 1 compression with that camshaft. That is a very mild cam and makes plenty of vacuum in a 350 engine build provided the pistons aren't way below the deck and TDC and you put a thick head gasket on it. The compression ratio should be over 10 to 1 with tight quench and with that cam you should be seeing plenty of vacuum at idle speed and full control of idle A/F with the mixture screws with the stock carb set-up.
Since the 207 carb is a factory "hot-rod" I don't open up the MAB's when building them here. Instead I'll employ the APT system and go up one or two jets sizes from stock and larger .042" primary rods, then use the APT system to fine tune part throttle A/F.
Just curious what rebuild kit you used? Mine would have contained the correct high-flow N/S assembly. Using a smaller one will effect the fuel level at any setting/pressure and lean it up a bit everywhere. The float setting is a big deal with tuning so make sure you aren't setting it too low or using the wrong N/S assembly.........Cliff
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Thanks for the quick reply. I've visited you site for years looking for suggestions. This is the first time I've submitted a post.
I've played with q-jets for years (since the 80's) and this one has not responded the way I was expecting. It is a service replacement carb. I believe the date 1074 indicated a 1984 carb. The only reason I went to the A/F ratio tester is because nothing else I tried seemed to work.
I've checked/adjusted almost everything on the setup over the years. The distributor works best at 9 btdc. Float settings from 3/16 to 1/4 (at 3/16 now). From stock 66/36 jet/rod to 69/39 jet/rod, to the latest at 71/67. Double checked all the settings and adj those that needed adj..
The only modification to the idle circuit was to open up the bypass from .093 to .098, which did not make much of a difference. All other idle specs are as they came on the carb. None appear to have been modified.
It had 186 heads with a factory 10.5 comp ratio, with a 350 hp 350 cam. But the engine would "run on" with 91 pump gas. I had to leave the trans in gear to get the engine to stop. I changed the heads to a larger chamber volumn to stop this. I calculated compression to around 9.10. This is a factory 1969 350 4 bolt main block with the original chevy std pistons. When I took the engine to be cleaned the machine shop offered $1000 to buy to. They said the block casting was used on Z/28 and desired by restorers.
The engine has good vacuum. With the 350 hp cam, the vacuum was around 15. After the head/cam change the vacuum is around 16.5.
I did not expect the jet change to do what it did. It was the last thing I could try without modifying the idle circuit. I can go back to stock jetting/rod or anything in between. I have a large selection of quality used early q-jet parts that I've collected over the last 40 (yikes) years. Weekly trips to the yards for late 1960 chevy parts can do this.
So, besides changing to an adjustable apt, what other changes would be advisable? I have the tools to modify anything on a carb.
Ps. I've purchased dozens of rebuild kit over the years from different manufacturers. A few have had the larger N/S. Most with widows, some without. I always check gaskets to make sure no required passages are blocked. I don't recall what's in there now.
Pss. The car is a camaro ss with 350, auto, P/B, P/S, and A/C.
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ALL of the rebuild kits you are buying in the past 15 years or so come from the same source. They will NOT have the correct high flow N/S assembly in them and it should NOT have windows in it. They blue pumps seals are "soft" as well, and why I have good USA ones made with a lifetime warranty on them.
I would recommend one of my kits and set the float to 1/4". I also have the "orange" PP spring reproduced and would put one of those in place as well.
Go back to the small MAB's and close to the stock jetting. With this new fuel it helps to increase delivery by apprx 5 to 7 percent across the board. Install one of my adjustable APT screws in the baseplate so you can nail down part throttle A/F without pulling the top off the carb and changing parts.
Pull the idle tubes to make sure they are not varnished up and size them at .038". Nothing else in the idle system would need any help for what you are doing.
Lowering the compression ratio NEVER helps for power production (torque). The factory 186 heads are excellent, right up there with the excellent 041 castings used the same year. The combustion shape is excellent and they will do fine on pump gas at high compression ratios with the right cam choice.
Those 327/350 and 350/350 engines will run fine on currently available 92-93 octane without running hot, overheating, pinging or "running on" with careful tuning. The factory really did know what they were doing when they designed cams for them. They also used .020" thick steel shim head gaskets and pistons near the top of the block at TDC to keep quench really tight. Most folks miss the mark considerably building those engines putting the pistons deeper in the block and TDC and using a .040-.060" "builder" head gasket on them. That NEVER works out well.
Neither does lowering compression and going to a smaller cam (short seat timing, tighter LSA and earlier intake closing point) with a point or so less compression just kills off power (torque), pulls power down in the RPM range, and considerably LESS upper mid-range and top end power.
I prefer to use the 327/350hp cam in 350 builds with 64cc heads, squish around .035" or so, and 10.5-10.6 to 1 compression. You will have a hard time finding a cam from anyone (doesn't matter what they tell you) that will idle better, and make as much power at any RPM over nearly as broad of an RPM range. Another excellent cam for the later blocks is the GM LT4 "hot" roller cam with high ratio rockers on it. Comp Cams wishes they could grind one that works as good but they insist on going tighter with the LSA so the end user has "menacing" idle quality, not the most power at every RPM with a smooth idle and more vacuum for power brakes, etc.......
The "run-on" deal comes from not quite enough initial timing combined with not quite enough idle fuel and bypass air, or a little of all three.
The current engine in my car is 11.3 to 1 compression, 200 psi cranking pressure, 13.5 vacuum at 700rpms and manages pump fuel now since 2009 with zero issues anyplace. IF I drop back to 87 octane fuel it runs fine on it, but will also "run-on" once in a while but only on really hot summer days with the engine fully heat soaked.
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Thanks for the suggestions. I'll order the rebuild kit, adj apt kit and return jetting close to original. The carb was very clean when I bought it. I used long shaft numbered drills to measure the idle tube size, .039 fit - .040 did not. I also ran a slightly larger drill in the tubes to make sure they were clean. They were. The carb has the original short pp spring. Is the orange pp spring different? Can I get by with changing the upper mab and leave the lower mab alone.
I live in Calif and 91 octane is highest available in my area. Also, a gallon of 91 octane is over $5. Gets real expensive when you go for a drive. And the state keeps changing it's formulation over the years to make it "cleaner". My cars run hotter and get less gas mileage. One one the reasons I try to build an engine to run on 87.
Which brings me to another observation. When I pulled the 186 heads, all of the exhaust valves were bright white and you could see where the heat discolored the head about 2" around the exhaust valves. I had 67 jets and 36 rods in the carb at the time. I changed to 69 jets in the hope the engine would not run so lean. Any suggestions on how to tune the carb for Calif reformualted gas.
I agree completely with your comments about using the 350hp 327 cam. My machine shop also recommended the same. They rebuilt my 1968 camaro vert 327 / 4 speed using the 350 cam. They decked the block to get zero deck height with the 30 over pistons and shaved the heads to get a clean flat surface. The engine started as a 275 hp 327 with 291 heads. After a little tuning the car is a blast to drive. Runs smooth at 750 idle, does not "run on" with 89 octane, revs easily to 5500, and never went hotter than 190 degrees on the drive up the sierras to Hot August Nights. Which is why I could not figure out why the 1969 ran so badly.
I use the 69 camaro for cruising. So max power is not a priority. Just clean running. When I have a need for speed I jump into my 1969 Nova SS 396, which has a stong 454 in it. 😁 And all have q-jets.
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bob69, I tried to send a PM but your message box is full...??..
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Quadrajam, sent you a pm. Did you get get?
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Yes, thanks. but was unable to reply. Check your e-mail and see if that worked.
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Finally rebuilt the carb using one of Cliffs rebuild kits. The MAB and idle tubes were changed back to their original sizes. The jets were changed to 68 (stock 66), rods changed to 39 (stock 36). Float set to 1/4. The engine started right up and ran good. Had to turn down the throttle screw as the idle was high. About 1/2 turn. Idles good at 820 in park - 600 in drive.
Idle vacume is relatively stable at 15 inch. The steadiest reading has the idle screws at 3 turns give or take 1/16 turn.
Light acceleration is about the same. Really jumps off the line. Most likely due to timing. Initial set at 11°. Timing goes to 17° at 1000 rpm. Distributor vacuum advance pluged for the test.
Moderate acceleration is not as good as before. Seems down on power. Just don't know if the jet/rod combination is lean or rich. Heavy acceleration is also down some from before. But need to work out the moderate acceleration first.
Cliff, the engine still has a tendency to run on. Just not as bad. I think the timing is ok. Could the carb be lean?
Can you explain a little more on the APT. What impact it has on idle, cruise and acceleration. I measured the original apt height before replacing it with your adjustable APT set to the same height.
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APT changes the metering area at cruise, or light engine load. You MUST use the vacuum advance to tune with the APT, otherwise your engine is missing a lot of timing and can not effectively burn a lean mixture.
Hook up the VA and start over. I would also replace the primary rods with 42B-44B's. Since you have APT you can raise them up and richen things up if/as needed, but will have more control leaning it up.
Running on typically means the throttle is too far open at idle. This can be caused by not enough timing, not enough idle fuel, bypass air or just the idle speed is too high.......
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Update. WOT was too lean with 68 jet on E10 gas. Changed jets to 69 with 41 rods. Better wot but lean in part throttle cruise. Turned apt 1/2 turn richer and pt cruise now running in mid to high 14s. Turned idle screws down to 2 1/2 turns to get best idle (was 3). Set drive Idle speed to 600 rpm and park idle dropped 100 rpm to 700 (was 800). Idle af in 13s. No longer have run on.
Still have one issue to figure out. The af goes very lean momentarily when throttle is opened. This happens at all engine speeds, from idle to steady cruise, when throttle is opened. This reflected in the af meter readings/recordings.
The accelerator pump was adjusted to stock measurements at 5/16 from air horn to top of plunger (measurement was 6/16 before adj). The af does NOT go rich. The check ball from the kit was used. I see fuel coming from the shooters with the engine off.
The choke pull off provided no delay at all (parts store replacement). This was causing a major stubble on fast acceleration. A brass restrictor from an old choke pull off was inserted into the hose to the pull off. The delay is now about 1 1/2 to 2 second.
The secondary air valve rod was adjusted to keep air valve closed when not needed. Air valve spring set to 1/2 turn.
What else should I look at to fix this monetary lean condition.
I think this is part of a larger issue as acceleration is not what I expected. I have another car with the same cam profile in a 396. Even with the displacement difference the acceleration (in a 350) is still too low.
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"Update. WOT was too lean with 68 jet on E10 gas. Changed jets to 69 with 41 rods. Better wot but lean in part throttle cruise"
Wot should be adjusted with secondary rods after the primary side is figured out.
"Still have one issue to figure out. The af goes very lean momentarily when throttle is opened. This happens at all engine speeds, from idle to steady cruise, when throttle is opened. This reflected in the af meter readings/recordings."
How much throttle opening ? What is very lean?
Cliff said
"Second I would quit chasing the A/F meter and tune for best results instead."
I believe Cliff is making this statement because some people do not understand what A/F ratio's should be at..... idle/cruise/light acceleration/wot...
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old cars, the afr I'm getting is in the mid 16 range. This is lean especially since the afr should be rich due to the extra fuel provided by the accelerator pump. I see this at all throttle opening rates, from idle to steady cruise.
I learned some time ago that trying to tune by afr does not give the best performance. This is based on first hand experience tuning my four classics. Three 1969s and a 1968, all chevys with different v8s (327, 350, 396 and 400). All have/had q-jets.
Lars has an excellent write up on how to tune a q-jet that I follow. He is a well respected Corvette tuner and has written several articles on tuning corvettes.
Back to my current situation. I use afr to help identify possible problems. I'm not seeing a momentary rich spike as expected when opening the throttle. I see the monetary rich spike on the other three q-jets. I don't see why this one does the opposite.
The car's acceleration does not come close to what I see for the other cars. I want to fix this before moving on to other tuning adjustments.
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AFR ratio going in to 16 range on light acceleration with a quadrajet is quite normal. A jab of the throttle may show the accelerator pump (richness ) momentarily. I tune with AFR all the time. I don't usually need AFR to identify possible problems.
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Is the power piston free? Does it have the correct spring?
Correct length rods? Hanger height normal?
Does the acc pump shoot a strong squirt the entire throttle opening?
Did you restore the air bleeds back to stock?
I'm running out of ideas. Must be a tough one.
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Quadrajam , I'm running out of ideas too. I hope someone can steer me to a possible solution.
To answer your questions: power piston is free and has the stock pp spring that's orginal to the carb. It's also the same size pp spring as found in the other 207s I have. Rods are stamped with B indicating the correct lenght. Hanger not damaged or modified. The accelerator pump shot looks strong when throttle is opened (but I can not tell if its ok while driving).
The MAB were increased from 0.050 to 0.070. This change is what caused the problems listed in the original post. The MAB were changed back to stock. This fixed those issues. The IAB were not modified.
For the lean condition, I have an innovate lm2 to record the afr. Been using it for over 10 years on several q-jets on different cars. On each of the other q-jets, I see a momentary rich spike when opening the throttle. A spike that lasts about a second. Showing the effect of the accelerator pump shot.
So when i say I see a lean spike its for the second or so following the throttle opening. I suspect it's contributing to the weak acceleration I'm having. I've seen this before.
On one occasion I found a lean condition when opening the throttle that turned out to be an out of adjustment pump rod. I adjusted the rod and the rich spike showed up. Acceleration improved.
On another occasion/car, the car had not been driven is several months. The afr showed a lean spike on opening the throttle. This time it was enough to cause a mild lean stumble. Turns out the blue accelerator pump cup shrunk and was not pumping. After about 20 minutes driving, the cup expanded and sealed. The lean stumble went away and the rich spike returned.
Old cars, I also see the lean condition on light acceleration. But it may be too lean. E10 runs leaner. The stoic afr for e10 is 14.1 not the 14.7 for gas.
If i understand it correctly,, Stoic is the theoretical ideal afr for the fuel. The lm2 uses 14.7 (gas) as the default ideal afr. But stoic for e10 is 14.1. The lm2 readings must be adjusted for the the difference. A 16.0 on the 14.7 scale converts to 16.7 for e10. A little too lean.
The lm2 records lambda and converts to afr. Lambda is 1.0 for the ideal fuel/air ratio, regardless of fuel type. 1.0 is converted to 14.7 afr for dislpay. I would use lambda but it's a whole different language.
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If it's too rich & it stumbles it will show lean. Any misfire shows lean, because of unburned oxygen.
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Maybe 77 cruise is onto something with the misfire idea.
Is the mechanical advance free and smooth?
Do you have another carb to swap out?
Another distributor?
Some crazy ideas yeah but we gotta whip this thing.
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I will try to comment/explain without being offensive , so don't take this the wrong way.
First of all you started drilling an innocent carburetor.
Second you changed main jets to address idle fuel ?
Then you changed main jets To address WOT?
Now your explaining Lambada/AFR?
Can you feel this lean condition as a hesitation if you taped over the AFR gauge?
"There is no reason to run an engine at part-load any richer than as lean as it will run without misfire. Of course for each engine just what that AFR may be depends on the particular engine’s characteristics, cam, compression ratio, headers, mufflers, etc. The biggest factors are uniform AFR distribution to the individual cylinders and exhaust reversion through the valve overlap. At part-throttle, distribution is affected by throttle angle and other carb geometry as well as the manifold, manifold heat, fuel distillation curve, etc, etc.
Between about 10% to 20% and 70% to 80% load some engines will run well at part-throttle with 17/1 AFR or leaner and others start to turn bitchy at 15/1.
You need to realize that the leaner the AFR, the larger percentage of oxygen in the exhaust. When running at part-throttle the high intake vacuum is drawing hot exhaust back into the intake manifold. Leaner than stoichiometric the excess oxygen in the exhaust is returning to the cylinder in the reversion gasses and the hot oxygen improves combustion.
Obviously, the leaner it is, the larger the proportion of unburned oxygen in the exhaust will be, and up to a point (unique to each engine) the lean running usually noticeably improves the part-throttle combustion.
Depending on your particular engine’s nature, you will be surprised how much part-throttle torque improves as it is operated progressively leaner on the lean side of stoichiometric. The limit is usually reached when the leanest cylinder misfires.
Because lean part-load mixtures have a slower combustion rate, they require additional spark advance, compared to rich maximum power WOT mixtures.
Correct vacuum advance tuning is as important as carb tuning. If the timing isn’t correct, you can chase the carb tuning into a box where a rich cruising AFR is wasting gas, because, without vacuum advance, a faster-burning richer AFR compensates for retarded timing.
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continued
You have to use common sense applied to your particular engine to determine at what amount of load the engine should be switched from the lean economy AFR to the rich power AFR. The power valve opening point and the vacuum advance starting point (fully retarded vacuum amount) should usually be near the same intake vacuum.
A high compression engine that is close to stressing the available octane, such as a 10/1 mild-cam street engine on pump gas, like a muscle car engine in the late ‘60s, may need to be rich and retarded at 9 or 10 inches Hg.
A low compression engine may not need to richen up until much closer to WOT and may tolerate the vacuum advance not fully retarding until as low as 5 or 6 inches Hg.
Because lean mixtures burn slower they require the correct amount of additional timing, compared to rich WOT mixtures. The correct vacuum advance is a key to lean part-throttle tuning."
On the lean side of stoichiometric, as the AFR is made progressively leaner there is a larger percentage of unburned oxygen in the combustion gasses. As the mixture is leaned, the increasing amount of (now very hot) oxygen in the residual gasses improves combustion.
Generally, as you jet leaner, the small throttle opening area (light load, vacuum above about 8” or 10” hg.) some engines will get crisper and actually get more power with less throttle, up to 17/1 or so (indicated on a WBO2) before the ‘fishhook’ phenomenon of increased consumption occurs. Some engines with excellent distribution respond increasingly better as high as 18/1, while some engines with poor distribution are struggling at 16/1. The break point is when the leanest cylinder misfires. Before smog tuning began in the mid 60s, most old-school OE engines were tuned to run at about 16.5-17.0/1 up to 50%-75% load. The extent and characteristics of this phenomenon, of course, depend on the valve timing and headers, backpressure, etc, and varies from engine to engine.
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It will help to understand this about the sensors. On the lean side of stoichiometric there is an increasing amount of nitrogen oxides in the exhaust product. The O2 sensor is affected by the presence of the oxygen in the NOx and is reporting a leaner AFR than there actually is. This is not a fault of the sensor or sensor system of any manufacture. It is the physics of the catalysis and ion pump processes by which the sensor itself operates.
The clue here is rich idle, lean cruise, leaner (leanest, actually) part-throttle acceleration and rich WOT. The leanest is at mid-load, half-throttle or so.
The tuning goal is to find the leanest mixtures which the engine will tolerate without missing or surging in level road cruise and moderate to intermediate acceleration. As load is increased engines will tolerate leaner A/F. Flat level road load will nearly always need to be richer than ¼ or ½ throttle acceleration. In fact, the closer to WOT, the leaner an engine will run, although approximately 15% richer than 1λ A/F (12.5/1) is necessary for best power and engine safety.
The thing to understand is most engines respond to being leaner than stoichiometric at part-throttle because the lean exhaust gas has hot unburned oxygen, and hot oxygen improves combustion.
Using a WBO2 and a vacuum gauge to monitor this you will see improvement as you adjust the primary main jet to find the best A/F for moderate acceleration in the load range between a level road, perhaps 14-12 in. hg. and the point where the power valve opens (Metering rods)I, perhaps 8-6 in. hg. The engine's part-throttle acceleration will noticeably improve as the AFR is adjusted to the lean side of stoichiometric.
When the air bleeds are configured correctly the A/F will progressively become leaner (from the rich idle) as the throttle is opened, until reaching the low vacuum load point where the PV opens.
The key thing is, at moderate to mid load, engines will run lean and like it, and burn much less gas while doing so. They must be rich at idle and very low load, lean in the middle, and rich at WOT.
And if you think this does not relate to performance you will be mistaken.
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Thank you to "Tuner" for the above explanation.
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Wow! Long read but not sure it will help out much here.
Since I got into this hobby the trend has been to reduce timing at light engine load and throw MORE fuel at the engine to keep things happy.
Hence MSD sells butt-loads of billet distributors w/o vacuum advance and when you walk thru a car show with 250 carb present at least 235 of them have a gas sucking Holley or POS Edelbrock AFB clone sitting on them!....FWIW.
NONE of those folks complain in the least about idle quality, throttle response and if you stick around their car long enough you'll start to hear tails of how it ran 10's at the last track rental they attended even though I can look right at the combo and see that it would have a hard time getting into the 13's unless you dropped it out of a C-130!
Just some humor, but there is some truth there if you can read between the lines. I've followed this thread a bit and not understanding how one of the best set-up Q-jets to ever leave the factory (7029207) needs much help anyplace to work FLAWLESSLY on this engine combo. I've built more of those than anyone who will read this and rarely deviate much if any from the stock calibration. That simply happens because most of them end up on engines that have a small cam upgrade over stock and the 207 carburetors were calibrated for the 350/350hp engines which basically are the same thing but they were smart enough to INCREASE the compression ratio in conjunction with the larger camshaft to offset looses and efficiency from the added seat timing and overlap.
Typically when the 207 carb is used with flat top pistons and 64cc heads, even if the builder was smart enough to keep quench really tight (most are not) it does well enough that few if any additional modifications are needed to the idle system to keep thing happy. I will add here that not all 207's have the exact same set-up, so this changes things a bit when it comes to building and modifying one for any specific application. All 207's did come with smaller main jets and primary B series rods. This was done because the larger idle tubes and DCR's bring in MORE fuel as the throttle plates uncover more transfer slot contributing additional fuel at light engine load.
....continued
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Typically here, when I build one at most I'll go one jet size larger and slightly larger primary rods plus make the APT adjustable for full control of the primary side A/F from rich to lean. This is only done to make up for the lack of BTU's and lesser quality of this newer fuel compared to what those carbs were originally set up for. There is never a need to open up anything else for most engine combo's, so the IAB's, DCR's, MAB's etc stay at the stock sizes. It's a factory "hot-rod" carburetor so really no need to try to help it be any better, they are very, very good right out of the box.
IF you are having issues with one, and I've not ran into that problem to date, there may be other things at work here. Might be time to go back to basics and make sure that it doesn't have fundamental issues someplace. I'd start with making sure the secondary throttle plates are fully seated in the bores and little if any light showing around them. Make sure the baseplate is the correct part number. Not uncommon to see the wrong one in place as many got swapped out decades ago due to being loose at the primary shaft. Verify that the primary shaft isn't "twisted", very common problem if anyone ever tried to remove the choke parts from the end of the shaft without holding them with something to keep the shaft from twisting.
I'd also pressure test it to make sure it isn't leaking at a bottom plug or leaking from the main fuel bowl over into the passages below the DCR's. I've found a few that did this and it makes them IMPOSSIBLE to tune.
Double check the power piston hanger arm height and they MUST be exactly level and even. I get troubled carbs in here all the time and every single one has bent hanger arms and rods uneven in the jets even when the person building it has assured me that they are not.
Also make sure that there isn't a bunch of "monkey chit" (epoxy) smeared over the bottom plugs keeping the baseplate from fully sealing the gasket. I see this ALL THE TIME because every "guru" on every Forum, Youtube or blog out there tells folks working on Q-jets to smear a pound of JB Weld (useless for holding back fuel) over bottom plugs that were pressed/swaged in place and not leaking in the first place.
Once every thing is checked and found to be in perfect working order I'd put the carb back to stock, including the float height and start the testing/tuning process all over again. I'd also (taken from the lengthy thread above) incorporate vacuum advance tuning into the equation plus use your APT system for fine primary side metering changes as well.
If you can't dial it in at that point it may be time to scrap it and look for another unit. I've ran into a few carbs over the years that just weren't going to work no matter how much time we spent with them. Could have been something as simple as they got the wrong nozzles installed on the assembly line or they were driven too deep into the casting (have seen this a number of times over the years).
In any case when you use good parts, and everything checks out, and it doesn't work well despite your best efforts it may be time to jump off the sinking ship.......FWIW......Cliff
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Wow old cars, lots of good information to digest.
I agree each engine combination requires it's own tune. I have four different engines, each built for a different purpose. The tunes are different. Each is tuned to give the best idle, cruise and wot performance.
The first rule for carb tuning is to get the distributor timing correct. Before any carb adjustment I'll record the distributors timing from idle to 4000 rpm in 500 increments. I'm recording total advance (initial and mechanical) without the vacuum advance hooked up. I start with 10° initial and see what the total is. If total is greater than 36° the distributor is modified to get total to 36° or less. If timing advance starts before 1000 the advance weight springs are stiffened up. I only use vacuum cans with a 15° limit. All cars have the vacuum advance hooked up.
Would you use 16.0 afr target with e85? I think not. Calif has e10 but adds a boat load of oxygenators. As much as 10 - 15%. About four years ago calif mandated yet another fuel formula change. All my cars started running rough. More oxygenators less gas.
I had to retune all the carbs. For example, it took me two months and many tanks of "gas" to get the set up correct on one. I tested jets from 71 to 75. Settled on 74s as the performance was noticeably best. Even retested 73s and 75s to confirm 74s were the best. The point being that I use seat of the pants testing and not afr to tune a carb. Interestingly, the 74s gave the best overall afr's.
I agree that misfires will increase the o2 levels the afr testor see. I do not hear any pings but its possible. Will test with 91 to see if that helps. By the way, 91 goes for $7.00 a gallon around here. Consider yourself lucky you're not in calif.
Regarding your opening comments. I do not do things willy-nilly. The mab were changed following reciipe #1 on page 111. The idle circuit was not altered, based on comments found on this site. When I tried the large jets it was a last chance to test the set up before making any permanent changes elsewhere. Also, jets in the 71 - 73 range for 0.070 mab are recommended on recipe #1 on page 111. And finally, the oversized jets privided the best idle quality. Very smooth and afrs in the low 14s. With the mab and jet changes, the afr had to be 13.0 to get close to the same idle quality. Still not as smooth.
I still do not see any explanation why I see a momentary 1 second lean spike when the throttle is first opened. My other carbs show a momentary 1 second rich spike. Perhaps Cliffs comment that this carb may be a pos and use another carb is right. Just don't like writing it off without an explanation.
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Carburetors are "stone-age" technology and need to be treated as such.
A/F meters or Lambda devices are too sensitive to evaluate what happens in a carb due to no computers for fuel/timing control.
What controls a carbs ability to deliver a proper combustable mixture due to atmospheric pressure into the void in intake are the various openings in each circuit inside the carb to mixture air and fuel adjusted to the current vacuum signal strenght. There will always be a delay, larger or smaller, depending on speed of throttle openings that the A/F meter/Lamba device will notice that in reality mean little or nothing for the performance of the stone-age carb.
There is seldom if ever needed to alter the main airbleeds.
Adjust if needed the main jetting from the main airbleed sizes.
Since you have Cliffs book take a look at pages 97-98 "Primary Main Fuel System" and you´ll get an idea.
Also, on page 99 Cliff describes the "tip in" procedure. Have you done this?
FWIW
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bob69
Answer this question. When you see the " lean spike" do you feel a hesitation / stumble
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Carburetors are "stone-age" technology and need to be treated as such.
A/F meters or Lambda devices are too sensitive to evaluate what happens in a carb due to no computers for fuel/timing control.
What controls a carbs ability to deliver a proper combustable mixture due to atmospheric pressure into the void in intake are the various openings in each circuit inside the carb to mixture air and fuel adjusted to the current vacuum signal strenght. There will always be a delay, larger or smaller, depending on speed of throttle openings that the A/F meter/Lamba device will notice that in reality mean little or nothing for the performance of the stone-age carb.
There is seldom if ever needed to alter the main airbleeds.
Adjust if needed the main jetting from the main airbleed sizes.
Since you have Cliffs book take a look at pages 97-98 "Primary Main Fuel System" and you´ll get an idea.
Also, on page 99 Cliff describes the "tip in" procedure. Have you done this?
FWIW
Kenth
Not sure I am understanding your first paragraph. Can you elaborate
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I completely agree with Kenth about using A/F meters to tune these engines using carburetors and conventional distributors with VA.
Before you get your bricks out and start throwing them at me hear this out.
In any and ALL cases we tune for best results in every area. Idle tuning comes first, but it is done in conjunction with finding the ideal initial or base timing.
It's super easy to dial in the ideal idle mixture the engine wants, and you don't need a vacuum gauge or hand held tach. Just listen to the engine. Back the screws out till noticeably rich but not "blubbering". Turn them in until you just notice a speed change or the engine starts to become slightly "rough" or unhappy, then gently back out till it cleans up nicely and smooth again. Do both sides, "balance" them if/as needed, DONE with idle mixture. You can gander at your A/F meter at this point, but no matter what it says the reading is what your engine wants, likes, and responds best to.
I like to tune the primary main jet next. This may take a few tanks of fuel as described above but we need to NAIL DOWN the most ideal jet size for heavy throttle without the secondaries.
Move on to the primary metering rods. IF you have the idle fuel system nailed down and your "recipe" includes metering rods providing full control of A/F from rich to lean, which it should, start out lean (APT down/metering rods deep in the jets) and start driving the vehicle. Realize that the vacuum advance and mechanical advance are "players" here so running leaner mixtures will require the ideal spark lead to effectively burn them. I've spent days and even weeks nailing down the ideal settings for timing and part throttle APT settings.
I was always thinking that a lean mixture would net the best fuel economy, but found that with these things it's difficult, if not near impossible to get past the basic laws of physics. It's simply going to take a certain amount of energy to move a given mass a given distance. So going noticeably lean has NEVER once resulted in the best fuel economy combined with the best throttle response, acceleration, and power for all "normal" driving scenarios. I'll add here that I've installed A/F monitoring devices and was actually quite surprised by the readings I was seeing compared to the actual test results. This is where monitoring becomes difficult. Long-lengthy reads on the subject, following resident "experts" on Forums, and others who do testing in these areas throw monkey wrenches right into the middle of that deal.
What is my "target" A/F is the first thing you need to ask yourself? Am I looking for a "fixed" number, like 12.5 to 1 for WOT? Or will my very efficient and well thought out engine build be happier with 13.2 to 1? Or 12.8? How about part throttle A/F, is it a magic number like 13.5, or 13.7, or even 14.2 to 1?
I was seeing a WIDE range of A/F in the "normal" driving range at times going clear up over 17 to 1, and my engine still operated FLAWLESSLY. Throw that number into most of these conversations if you want get the natives all stirred up!
continued....
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Another thing few if any folks realize with these things is that a carburetor is a metering device an it is NOT, and I will repeat NOT a "fixed" delivery system. By design, and I absolutely LOVE this part, it will vary fuel delivery based on throttle position, engine load, air flow across the venture/boosters and pressure differential above and below the throttle plates. Very clever these engineers were with designing them and they are very effective at not only fuel delivery in the correct proportions but also very fine atomization of the fuel molecules BEFORE they hit the intake tract an make it to the combustion spaces.
I'll slow this down a bit but anyone reading this needs to understand the importance of finding the best "recipe" for your particular combination. This includes a lot more than just setting up the carb and distributor. There are a LOT of other players in the game and things effecting the final outcome. To mention a few is the compression ratio, combustion chamber shapes, camshaft events, intake chosen, spacers used, scavenging efficiency of the manifolds, headers and the rest of the exhaust system. I'd also mention engine temperature (thermostat setting and actual temperature of the engine parts) is a player here, plus the air induction system (heated or bringing in cool/fresh outside air). I'll go on to mention engine load from a "tight" converter, lower numerical gearing, vehicle weight, rolling resistance......etc, etc.
I certainly hope this doesn't "muddy" the water. Nothing at all wrong with using monitoring devices to help you in your efforts for perfection, but folks need to realize that they are simply tools to assist us and most to see the results of our tuning efforts. Used or not we ALWAYS tune for best results in all areas. IF you are using a Quadrajet in your efforts I have the knowledge and experience to help you cut very quickly to the chase. At this point in my learning curve I know all the part numbers, what they came with, how the factory set them up, and what is needed to dial them in for what you are doing. I can get you so close in most cases it's basically plug and play.
This is why I retired from carb building a few months ago and have moved on to selling parts, rebuild kits and custom rebuild kits with tuning parts. I've spend the time and funds to make sure you get the best parts out there, the correct parts, and tuning parts needed to dial you in, or basically "plug and play" right off the bench.
So as these discussions go on folks should realize that this is NOT something you can nail down going out and buying an A/F metering and simply monitoring. You are going to have to spend some time with your set-up to nail down the best overall results. This Forum is there to help you that effort........Cliff
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Hey all, I appreciate the discussions. Never too old to learn something new :).
old cars, the car does not "hesitate" as such. But it just does not accelerate like it should. Slow uptake in that first second or two. The acceleration after that is ok but again kinda weak for a 350 when compared to my other cars.
I had a 1969 nova with a nicely built 454. It would smoke the tires easily from a standing start with just 1/3 throttle. I got real good at rolling starts before hammering it. Very strong motor, plant you in your seat real good. I had it at a 1/8 track once. Ran 93 mph with a rolling start. It had a 7029207 with mabs at .070. Ran great. Loved that car right up to the day it was stollen.
I had a 350 hp 327 with with a 7028213 q-jet. That motor would easily rev to 6500 quickly. Loved the way it would raise the front end when I jumped on it. The 350's acceleration is not even close to the 327. The same goes for the other chevys I've had.
At this piont I'll probably chuck the carb and try another.
Before I bought Cliffs book I followed the q-jet tuning steps outlined by Lars. His steps are basic the same as Cliffs. No surprise. So I've done things like tip in and removing a vacume line as tests.
As Cliff mentioned, you have to tune the ENTIRE set up not just the carb and distributor. For example, I scored a low mile GM remanufactured 700r4 from a 1990 nine passenger Chevy van. Took the gm rebuilt tq too. After the 700r4 / tq was installed the engine would not idle. To get a 650 idle in drive, the park idle had to be around 1300. After a lot of tuning and installing an idle stop solenoid the engine was still not running great at idle.
After much research I found that the 1990 nine passenger chevy van 350/700r4 tq had a stall around 1100-1200 rpm. The tq was dragging down the motor resulting in a too high idle rpm. Changed the tq to a 2200 stall. I dropped the park idle to 900 and drive idle was 600. The idle stop solenoid was removed. After some tuning to the carb the idle is silky smooth and the engine turns off when the ignition is turned off.
You may have heard the phrase - no replacement for displacement. Well experience is much the same. That's why I enjoy reading these posts. Never know what you can learn.
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It is hard to reflect sometimes what someone means as problematic online without seeing/touching/hearing in person because we all describe things differently.
AFR gauges (readings) can be controversial to say the least. I will agree there not for everyone. Even the installation location and leakage can affect readings. Not sure if I would call carburetors stone age. Maybe my posts have not been helpful. Good dicussions with relative information are always good though , even when it slides off the topic.
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I'll add that the WORST calls I get here are from folks who have installed A/F gauges and are trying to tune their carburetors.
They will call up here all upset and say things like "I saw 15.9 clear up to 17 to 1 AFR a few times cruising and changing speeds in traffic".
The FIRST question I asked was IF you noticed any hesitation, stumble, bog, "flat" or lack of power, surging, or any other negative symptoms. "No" they reply, "it seemed to run just fine". Then WHY are you worried about?
Well, I was over on the Chevelle Forum and a "guru" who posts there said that my A/F should be reading 13.61427427 to 1 at cruise or my carb was all messed up.
See what I mean? We tune for results, and certainly NOT what any resident "expert" posts on the subject.
The very same "guru" also told him that he can't use ported vacuum to the advance. I asked him why? "Because he said the engine will run hot, overheat, plus it will continue to add timing at heavy/WOT throttle, detonate my engine, crack the piston ring lands and knock all the rod bearings out of it".
LOVELY, another well educated "guru" that doesn't even understand how vacuum advance works and should as quickly as they can get back to their "day job"....IMHO.......see what I mean about using the Internet and an A/F meter to tune with.......FWIW.....
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Cliff, one last thing to check. Could the carb be draining the fuel from the accelerator pump well while running? What would the possible causes be.
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I’ll share some results: 454BBC /approx 500hp turbo 400/2.73 axle 227@.050 camshaft
First a Quadrajet
Idle AFR 13:1 Cruise 15.5:1 50mph 2100rpm Light Acceleration: 16.5:1 WOT: 12.5:1
Holley 780cfm (originally)
Idle AFR 12.6:1 Cruise: 13.5:1 Light Acceleration: 13.5:1 WOT: 12:1
After
Idle AFR 13:1 Cruise 15.5:1
Results will vary but these AFR ratios produced no hesitations or loss of power you could feel on the street.
The Holley carb stopped blubbering at lower speeds. WOT was not finish tuned at the time.
Idle fuel reflects camshaft being used. Idle vacuum was 12” approximately in gear.
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You will find the Holley carb (no mention as to part number, model, mods made to it or type of boosters used) more difficult to tune for part throttle A/F than the Q-jet.
You will NOT find your results changing jets and PV's. A large portion of the fuel at part throttle comes from the transfer slots as the large primary bores and inefficient booster design aren't in the mix like they are on the Q-jet.
I remember my early tuning efforts with Holley carburetors dating clear back to the 1970's. I remember locking the emergency brake and blocking the tires, putting the car in gear, then climbing up and bracing myself over the carb, looking down in it and watching for fuel to start streaming from the boosters as I applied load to the engine against the converter.
NOTHING....WTF? ALL the fuel was coming from the idle discharge holes and transfer slots, not the first drop from the boosters. The Q-jets I was tuning at the time, or attempting to tune as it was all a new game for me had TONS of fuel coming from the boosters in a nice cone shaped well atomized pattern with the slightest movement of the throttle off idle.
Hum? An early lesson in Holley tuning and by that time I had worn the bowl thread clear out of the main casting changing jet sizes in vain to try to get some decent fuel economy out of them. Not having any luck sent me into the air bleeds and then into the metering blocks. I got good at them early on then really good at them after a decade or so of tuning them to the brink of extinction.
By design I was never able to equal the Q-jet or the TQ's in fuel economy and seamless transition right off idle and for normal driving, but any heavy throttle movements without the secondaries was very impressive in comparison. This simply happens due to the much greater CFM available w/o having to get into the secondaries like I did on the spread bore units.
In later years I played around more with the larger annular booster Holley carbs and found them to be better in that area, but it comes at a cost of CFM lost stuffing a much larger booster into the larger bores.
I finally decided to pick a direction and run with it, so in 2003 when I went full time into the carburetor rebuilding/restoration business I dropped just about everything from the list and stuck almost 100 percent with Q-jets, but would take in a factory Tri-Power set-up (2-JETS) on occasion. That didn't last long and very quickly my backlog went out past two years. So I dropped everything but Q-jets, hired more help and we ran full time till a couple of years ago. Most of my employees moved on, I did not replace any of them as it became a perfect opportunity to retire and not have to put anyone on the street.
There's the short version of a long story but at this time I'm only selling parts, rebuild kits, and custom rebuild kits with tuning parts. I have the best accl pump seals currently available and NOTHING will make them swell up like the cheap soft light blue seals showing up from all the other sources.........Cliff
https://cliffshighperformance.com/simplemachinesforum/index.php/topic,4546.0.html
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I've been adjusting and testing for the past few months and finally worked out the issues. So here is a recap.
The original carb was defective. Tearing it down I found some sizable voids in the base plate casting. The voids were located inside the idle needle screw holes. Probably why the carb was showing a lean off idle afr spike. Also, this lean off idle afr did not show up in any of the three other q-jets I tested.
I tested jets from 67 to 71 with various rods. Except for one test, none of the tunes gave the performance I felt the combination is capable of. The one test, with 71 jets, smoke the tires for about 30 feet and then nothing. Like turning off a light switch, performance disappeared. The car ran OK at low engine speeds but had no performance.
It became obvious there was a problem with fuel starvation. The fuel pump was replaced about 5 years ago, so it was probably a restriction in the tank or fuel lines. On these older chevys, the fuel pick up has a strainer or "sock" to filter out debris. I pulled the tank and it looked new inside. Very clean. Pulled the sock and found it was almost completely plugged up. Don't know why. It was a replacement sock that came with the reproduction fuel pick/gauge line. Perhaps the stock's material was reacting badly with today's fuels.
Replaced the sock, blew out the lines with compressed air and replaced all rubber fuel lines. Did another test and still no performance. Pulled the fuel pump and found that the pumps internal plunger was partially stuck open. Limiting the pumps stroke and limiting fuel flow. Replaced the fuel pump. The fuel starvation problem was solved.
The 71 jets were now way too rich everywhere. Put in 69 jets which cleaned up the afr's and still has performance. May try 68 in the future.
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Good. So how are you liking those SUMMIT heads?
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At least you found the root problem. IMPOSSIBLE to effectively tune when fuel delivery issues are present. So basically you are back to square one.
The good news is that you can make predictable changes at this point........
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Quadrajam, the jury is still out on the summit heads. I've let the 200r4 control the shifting while testing. This 200r4 shifts around 4200 rpm on wot (a 1986 monte carlo 305 - not the SS). No where near what the engine is capable of. After I finish tuning in the carb I'll be able to see how they run at higher rpms.
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10-4 thanks.
Nice work finding the fuel pressure issue. That will
drive you nuts.
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bob69, My 2004R also shifts around 4200-4400 rpm even after I've done considerable governor lightening. It's a bone stock 350 engine but I'd like the WOT shift point a little higher. If you figure out a mod that works well, please let me know. Thanks.
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Von, the 200r4 is not an easy tran to hop up. Changing the governor weights is the easiest mod, but may not get you to where you want to be.
The vast majority of 200r4s were installed in low performance v6 and v8 grocery getters. The tran, specifically the valve bodies, were designed with early shift points for low performance engines. Modifying the governor may not be enough to get the higher shift points you're looking for.
However, GM did make a 200r4 for high performance buicks, oldsmobiles and chevys. They are found in Buick turbos, olds 442 and monte carlo SS. The valve bodies were designed for high performance. They were designed for higher shift points. From what I've read the low perf vb can not be modified to match the hp vb.
Look up the buick forums (turbobuick, gnttype, v8buick) for in depth information on the 200r4s. The buick GN and T-types have loyal followers and they love their 200r4s.
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Yes I knew all that about the 200 4R. I built mine. I was hoping to find out a valve body mod to raise the WOT shift points but sounds like unicorns. My part throttle shift points are perfect.
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The 200-4R's were also continuously evolving transmissions much like the 700/4L60 models. The factory continued to make improvements to them thru the years of production which included hard parts upgrades/modifications and also valve body improvements. For the most part the hard part upgrades were in place by 1986. Not all valve bodies are the same, nor are the separator plates. They even made mid-year model changes, so tread softly when you are rebuilding and/or upgrading your 200-4R transmission as you may run into differences between them not always noted in publicized literature on them. ATSG has been the most accurate in that area if anyone gets into trouble there.
It's been a while since I did one here, but I do remember it was from a 1984 Hurst Olds and the one I was into had an anomaly with the separator plate/check balls used but I can't remember exactly what it was since it's been at least 4 years ago and I suffer from bad cases of CRS and even worse cases of DGS these days.
Anyhow, over the years I've been into a good many of them. For the most part I made it a habit to upgrade all the "soft" spots even if it was a later model. The hardened/upgraded parts aren't really that expensive, and if nothing else you'll sleep better at night knowing they are in there. I also put aftermarket converters in them capable of handling a lot more power than the stock units, plus the triple disc option for the TCC if we were using lock-up. Doing so allows the use of lock-up under full power as early as the 1-2 upshift. This ceases all torque multiplication (the Buick 3.8 turbo engines love that deal) and puts all the power right to the pavement.
Overall they are pretty tough little units. I've had near perfect success with them here, other than having a customer burn one up in short order as his TV cable somehow got WAY out of adjustment and he was out hammering on it pretty hard........
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I'm running a CZF 200-R from an 86 Monte SS. Full throttle shifts are at 4900 RPM. Not a whole lot better than the Non SS trans. The 305 HO in the Monte was all done by 5K. I been running it for 10 years now behind a big block in a chevelle and it has held up quite well. I have broken one torque converter in the 10 years. A shop in the Akron Ohio area built it for me. It's the go to place for the Turbo Buick crowd. It's been a good unit.
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My CQ vb, I got the full throttle shift to 6400, but the part throttle shifts follow somewhat & are kinda high at anything but light throttle.
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Mine is out of an '86 Monte Carlo, non-SS. I used the Trans Go shift kit and other upgraded parts like 10 vane pump, Buick GN valve (I forget the proper name), wide band, hardened sun shell, etc.,and drilled the separator plate holes out to the max recommended by Trans Go. The part throttle shifts are very firm, especially the 2-3 (almost bang shift). The WOT 1-2 shift (about 4400 rpm) is softer than it should be and I've scratched my head trying to correct that for years and finally just live with it since I don't go WOT that often. I used the ATSG manual as a guide when building the trans. Engine is a well tuned bone stock low compression 350 with Q jet. Converter is stock replacement 1800 rpm stall. Rear is 3.36 posi in a '69 Chevelle. It runs very well for what it is.
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Von, were you able to confirm the valve body was coded CRG? And did the valve body have pink paint on it. The pink paint identifies the valve body as the monte carlo HP vb. It was used on CZ and CR transmissions.
I've read that the "pink" CR VB can be can be easily upgraded to CZ SS specs. Like modifying the governor to increase rpm shift points.
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The 200r4 discussions reminded me of the tests I did following the install (many years ago). I did a few tests with changing gears manually. At the time, the engine/trans would rev easily to 5000 in second and third. The engine was replaced when it developed low oil pressure problems.
The engine was replaced and same q-jet was used on both. The q-jet still had some of the same problems that were identified earlier in this post. Except this time I had no performance. If I had remembered that the q-jet did perform in the past, I may have identified the problems with "new" fuel pump and gas tank sock sooner. Live and learn......
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Fuel delivery is a BIG deal when it comes to tuning. I get all sorts of calls from folks wanting richer secondary metering rods because they are having high RPM issues with the engine going flat or loosing power.
Just had a customer in here a few days ago that had his carburetor "professionally" rebuilt/restored and it wasn't up to par for his big block Chevy 396 engine. I removed the airhorn and low and behold it had a .110" N/S assembly in it. That wouldn't keep up with a decent running 305 SBC let alone his "warmed over" 396!
Last time I looked it was 2022 and I wonder why folks rebuilding/restoring these carburetors continue to install the WRONG parts in them then blame the carburetor for not being good enough or big enough for what they are doing?............Cliff
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Von, were you able to confirm the valve body was coded CRG? And did the valve body have pink paint on it. The pink paint identifies the valve body as the monte carlo HP vb. It was used on CZ and CR transmissions.
I've read that the "pink" CR VB can be can be easily upgraded to CZ SS specs. Like modifying the governor to increase rpm shift points.
I found some pics I took when I had the trans disassembled for rebuild. The VB had CR something on it but the third letter or number was hidden. I didn't see any pink paint. The trans is from an '86 Monte Carlo 305 NON SS.
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Too bad you couldn't round up a CQ or CZ valve body. They have around 5000 to 5300 with a GN gov.
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Von, well that makes things more complicated. All of the posts I've read about the 1986 monte say the CR vb is made with the same basic core vb used in the CZ. The CR vb can be made to perform like the CZ with minor mods like changing shift springs, line pressure and the governor to the CZ piece. The govenor mods you made should have result in some rpm increases.
What's confusing is that performance vbs in 1986 monte were marked by GM with pink paint and you say yours was not. Now I wonder if the changes I planned to mine will be worth it.
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Von, well that makes things more complicated. All of the posts I've read about the 1986 monte say the CR vb is made with the same basic core vb used in the CZ. The CR vb can be made to perform like the CZ with minor mods like changing shift springs, line pressure and the governor to the CZ piece. The govenor mods you made should have result in some rpm increases.
What's confusing is that performance vbs in 1986 monte were marked by GM with pink paint and you say yours was not. Now I wonder if the changes I planned to mine will be worth it.
Mine could have pink paint on the VB, just maybe not visible in the photo I have. Mine has the Transgo shift kit in it so it has stiffer springs, etc. The gov mods did increase WOT shift rpm but just not quite high enough IMO. Maybe just needs more gov lightening. Since my stock 350 is all done about 4600 or so anyway it's not real far off. I don't feel like pulling the pan again anytime soon so it will do for now. I don't race it and don't go WOT that much.
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Mine did have the pink paint mark. Also had CZ stenciled on it in white.
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I don't know about a CR, if it's like a lot of other low perf. valve bodies it's almost impossible to get the shift points much higher.
The spool sizes are different in a hi perf valve body.
I had a OG & managed to get 6200 1-2 but 5800 2-3 & a bit under 5000 3-4.
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Von, send me a PM with your email and I'll send pics of my vb. The pink paint is obvious, so compare to yours. Hate to see you trying to modify the vb when/if it's one of the low performance models.