Cliff's Quadrajet Parts and Rebuild Kits
Quadrajet Problem Solving => Dialing in your rebuilt Quadrajet carburetor => Topic started by: Mudsport96 on February 17, 2017, 08:37:55 PM
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Like the title says, finally got around to putting it on the car. Cranked and cranked.. No start, what the heck it always fires right off no one pump of the pedal. Pump five times, fires runs dies. I'm about ready to give up and it hits me, it won't idle with the brake booster fitting open as a vacuum leak. Well, I feel stupid. So I hook up the line, half a crank and she's idling.
Super responsive in park, I'll let it get to temp tomorrow after work so I can set the idle screws and speed. But, I have till April before I can drive on the streets because of my seasonal plates. So I won't be able to do power and cruise tuning for awhile yet, which makes me anxious... I want to get it on the road haha.
But, that gives me time to do some manifold porting. I've found flow numbers for an as cast Performer RPM and for a ported iron Chevy quadrajet intake. And the ported iron blows the rpm out of the water, but that's another thread of its own.
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Well, got the car semi-dialed in. Idle is steady at 850 in park and 650-700 in gear. Its a little stinky at idle but, it always has been, I think that's from the 110 LSA and lowish compression of 8.2:1.
Vacuum is 12-13.5" at 850 and 21" in park at 2100 rpm. Did throttle tip in and had 300 rpm rise. Adjusted apt slightly and got a very slight rise so good for the time being.
As for full throttle runs off idle it has a flat spot from idle to about 1800.. I attribute that to the 1000rpm converter. Didn't notice it before the traction bars as it would spin the tires and pull as the tires gained traction. Now that it has traction immediately, it has to fight through the converter till it gets revs up to where the cam wants to pull.
I'll post up more later.
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So I got to going through my notes on this carb again, and I think I may have missed opening up the lower idle bleed.
Here are the numbers.
17057229
DCRs .050
Idle Tubes .034
Upper IAB .070
Lower IAB .063
MAB .050
Idle Bypass .125
Pri. Rods 44
Jets 73
Secondary Tube Rest. .032
Secondary Rods AU
Hanger J
Fuel Seat .135
You guys think opening the lower bleed to .070 will help lean the idle out some? Or is it that my camshaft on a 106 ICL with a 110 lsa could be the issue? Its also advanced 4 degrees so its really a 102 ICL.
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Sounds like it could be a bit lean. What's your timing set up?
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Its 14 degrees initial and 36 all in before 2300. Vac advance is currently inoperative, traced a vacuum leak to the advance canister, so its plugged for now.
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Sorry that was the old numbers. My problem is I have the specs written down on two pieces of paper, so a few specs are different.
SMAB .050
IDLE TUBES .035
DCR.050
MIX SCREW HOLES .077
Upper IDLE BLEEDS .074
LOWER IDLE BLEEDS .063
BYPASS .125
JETS 73
RODS 44B
SEC. RODS AU
SEC. FLAP SCREW @ 3/4 TURN
Reread the section on idle circuit and it said mix holes to be .090 for stock application. So maybe I'm lean at idle? Part throttle is good though, and off idle acceleration for normal driving that's not instant WOT is great
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How many turns are the idle screws out? Do they respond? Could go bigger on them.
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I'm wondering how you came up with .073" main jets with 44 metering rods?
.125" bypass air is already a pretty big vacuum leak for such a little engine.
If this is a "street" engine you need to use the vacuum advance, or it will require a LOT more in the "normal" driving range to be happy......Cliff
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Jim, they are 4 turns out.
Cliff, recipe 1 in the book calls for 74-76 jets and rods .030 smaller. Or later-style smabs with .060-.080 smabs 50-52-54m but this is the early .050 smab divorced choke with B rods? Am I wrong on that combo?
Also, I just have to get a new vac canister I plan on running vac advance, just have to replace it.
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The early divorced choke SMAB carburetors are tuned in a much different manner. They have an APT system in the baseplate as well, and we make a custom APT screw for them, so you can fine tune the part throttle A/F like the later designs w/o taking the top off the carb and changing parts.
Hopefully you have one of our rebuild kits in it, and I can spec out much better tuning parts when you are ready.
We also have excellent choke pull-offs for them, so you can dial in the release time to provide improved performance going to full throttle against the "tight" converter......Cliff
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Yep have your HP kit in it with the orange PP spring installed currently. You rebuilt the baseplate and installed the external APT for me. By the way, baseplate looks fantastic! Choke pull off is timed right at 2 seconds and it starts darn near immediately. I just couldn't get the stink out of the idle.
And yes the converter is tight.. I talked to tci and told him all the info about the car, and when he asked what it had in it for a converter I told him. He was so quiet I thought he hung up on me. And pointed out with the cam in it even though its small it needs at least a 2200 converter.
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For sure it would need more converter if you want the vehicle to leave hard on full throttle starts.
Those jets are HUGE for one of those carburetors and it will be putting down a LOT of fuel at heavy and full throttle with that jet/rod combo.....Cliff
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OK, well I'll try to get a call to the shop after I get off of work.
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I'd like to see about 10 deg. of vac. advance, to see how it responds.
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You're referring to 10 additional degrees at cruise, not manifold vac at idle?
So hopefully I will ba able to pick up a new vac can today and get it installed in the next few days. The 60 degree weather went away and its starting to snow now, so it may be put off for a few days.
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Try both, I like manifold vac. on my stuff, as long as it has enough vac. in gear so the timing doesn't drop.
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I use manifold vs ported vacuum to the advance on a case by case basis. Some engines don't want, need, or respond well to a LOT of timing at idle speed.
Others will like and some even require a lot of timing at idle speed. Most of those will be low compression with poor cam choices.
Every engine we build here is fine with around 10-12 degrees initial timing, aside from "full race" stuff of course. Most of those get a very short mechanical curve or "locked out" timing and no VA at all......Cliff
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Well, I'm still waiting for a new advance can to come in. Nobody, I mean nobody at any of the box stores have on in stock, its a two day wait to get one. So it should come in tomorrow and then I'll get around to installing it.
As for the timing, it idles best at 14 degrees. But then again that may change when I get the carb dialed in. But, 16 initial is the most she will take without kicking back against the starter. I will have to get my book out to see what the compression is but I don't think its I've 9:1 so that may be part of the idle issue as well.
Edit
The H345CP sealed power pistons (according to my sealed power book) gives me an 8.65:1 compression, but I don't know if that is with the standard .039 rebuilder gaskets or the .015 shim gasket that we used when putting it together.
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If you advance the timing with it idling, does the idle improve at all by going up to 20 or so?
I have a hard time believing it's kicking back on 16.
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The idle doesn't change much from 16-22 idle vacuum doesn't go up passed 16 degrees either. It has an Accel timing tape on the balancer, so no guessing at all. I suppose I can through the piston stop in #1 and double check to make sure the balancer hasn't slipped on the rubber ring.
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That would be a good idea. Mine likes about 28-30 at idle but I have a bit more cam.
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Jesus! 28-30 at idle? I ran a comp cams 12-225-4 years ago in a 302, and it only took 24 degrees at idle with a 260@.050 duration.
Well, I'll check it again and try bumping it up if it's not reading right.
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It's a 421 9.8 c/r 227 in. & 239 ex. 107 lsa. idles with 12 in. vac. @ 800 - 850
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We stock the good Vacuum Advance units and ship same day.
We will also modify them to any specs provided for a slight additional charge.
If it's "bucking" the starter at 16 degrees you'll probably have to drop it back quite a bit as it will only get worse in really hot weather and fully "heat soaked". I'll bet you'll end up closer to 10-12 degrees when it's all said and done.
Not surprised that it's doing that at all, the by-product of tight LSA and advanced intake lobe, short seat timing, and early closing intake. Those cams probably fair better in really "low" compression engines, at least one that small one would, IMHO.
I bought, installed and tested two of Comps "modern" lobe camshafts. The first was an XE268 cam in a very well prepared 400 Pontiac engine with 10 to 1 compression and ported #16 heads on it.
Those line of cams were HIGHLY recommended to be by a shop that specializes in Pontiac engine builds, so I tried one. I can't say TURD loud enough here. That engine had a "quirky" idle, noisy valve train, and threw OK power at you right off idle and lower rpm's, but DONE by 4800rpms and WAY down on power from what we had been using in similar engine builds. The ONLY good sound it made is when I "tinked" it off the dumpster outside the shop!
About 10 years later I ordered a custom XTQ lobed cam from Comp for my 455 to dyno test it against the Crower 60919 cam, 231/240/113LSA. The custom cam was 240/248/112 and had .060" more lift than the Crower RAIV clone cam.
The engine LOST 10hp/22ft lbs torque and quite at 5200 instead of 5600rpms. I yanked that cam out and NEVER went near another one of their "modern" profile flat camshafts. I've pretty much decided that all the "advertising" mostly "hipe" and about all you get from those cams are more "attitude" at idle and stinky exhaust. I'm not into how good the exhaust sounds standing behind the car, I'm into putting your vehicle WAY into my rear view mirror at the track!
Instead of putting the Crower cam back in on the dyno, I ordered $1000 custom ground hydraulic roller cam/lifter set-up instead, custom ground 286/294, 230/242/112LSA with .361" lobes. It should have KILLED the "old" Crower flat cam, but only made 3 more HP and 4 ft lbs torque.
At the track it did run quicker than what the dyno numbers showed as the car picked up about a tenth average run to run and nearly 2mph.
Best ever run with the Crower flat cam was 11.64 @ 116mph. The Comp custom roller cam went best of 11.52 @ 118mph.
So there is something to be gained by freeing up some friction and the engine revs quicker and vehicle accelerates faster with a roller set-up, at least that's what I saw here.
There is also something to be said for running a "long" duration cam with Rhoads lifters and high ratio rocker arms, it nearly duplicated the power of a very well chose hydraulic roller cam at much less cost!!.....Cliff
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Cliff I have been considering a different camshaft. But, I think I would want to upgrade the heads first. To get closer to 9.75:1 compression maybe 10:1 and go with the old 300 HP or 370 HP cam. However that will probably be a year or two off, as I just need to get some more miles on it. I'm going to pick up the advance unit tonight and install it then double check the timing. I'll get back to everyone late tonight or tomorrow. Thanks again for all the help.
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I get a LOT of complaints about camshafts from folks who contact the shop wanting us to work on their carburetors.
By far and above the Comp XE, Thumper and Mutha-Thumper cams top the list.
I've also had a lot of folks contact us saying they lost lobes on Comp XE camshafts, another reason to stay clear of them.
Back when those cams first came out the machine shop that I use bought one for an Olds 455 engine they were building. They do EXCELLENT work and very meticulous engine builders. It knocked half a dozen lobes off the cam before the engine had 50 miles on it!
I was also good friends with the owner and he assembled the engine. He had to do the entire rebuild completely over again, costing him a LOT of money and time. He never went near one of those cams again, and never had any issues since then either....FWIW.....Cliff
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Unfortunately, I wasn't able to get on the car last night with the daughters school stuff going on. Hopefully tonight I'll get to it.
And yes, I've heard horrible things about the XE line and Thumper line of camshafts, I plan on staying far away from them.
When the engine was done in 1999-2000 I don't think the XE line was out yet, so my uncle went with the High Energy line and the 268 was the biggest. For the few miles it has on it, it has always had fine street manners...minus the spool he wanted. But, now that I bought the car and spent more time with it I've noticed the little things, like the rich idle.
I would love to retrofit the engine to a roller hot cam, because I've read good things about that cam in a carbed application.... But, that's coin I sure don't have.
In the last few months a few of my friends have done rebuilds and I've pointed them away from the tight LSAs that they had been running and they are happier with the idle quality they now have as opposed the the 108 and 106 lsa they had been running.
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The "HOT" roller cam is one of my favorite camshafts for SBC engine builds. I also like the Speed Pro CS-179R grind.
It's a nearly duplicate of the original 327/350HP camshaft. It has long seat timing, up around 290-300, 222 duration @ .050" and .447" lift on a 114LSA.
You will not find a modern cam that will outrun either one of these very easily. They require high compression, tight squish and both are fine on a steady diet of pump fuel.
My favorite 355 cid SBC combination is to use a flat top piston, zero deck height, stock Felpro .039" blue head gasket, World Products 200cc Sportsman heads, and the CS-179R with Rhoad V-Max lifters and 1.6 ratio rockers. With 64cc heads and tight squish they usually come in around mid 10 to 1 for compression.
You will end up with a nice idle quality and plenty of vacuum for power brakes, good street manners, and power well past 6000rpm's. The power curve (torque) is very broad and flat with plenty of upper mid-range and top end power.
For truck engines we like a little lower compression so will use factory 441, 487, or 993 heads instead and smaller camshaft. I like the 350/300hp grind. Another very good choice is the "generic" 214/224/112 grind. I avoid the smaller "RV" cam at 204/214/112 unless the engine has very low compression like many of the stock 350's did with dished pistons and 76cc combustion chamber heads.
Lots of folks use the inexpensive "Vortec" castings, but I avoid them due to being very thin castings and crack easily, plus they lack the good features of the aftermarket iron heads like screw in studs, guide plates, etc.......Cliff
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Well, quick update. I haven't done much this week, got hit with mandatory 15 hour days at work. So, needless to say, didn't do anything M-F on the car and yesterday I did a 12 hour shift. So after getting off I put the new vac canister on and hit the key to start the car.... Starter is dead. It spins but doesn't kick the Bendix out to engage the flexplate. So I pulled the starter and grabbed new gear reduction one I had laying around, and went to install it and promptly fell asleep under the car. I guess 102 hour work week wore me out. I'll give another update when I get it running.
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What kind of work do you do? Never fell asleep under a car, but did one time having a root canal breathing the nitrous deeply. ;D
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Machine maintenance, maintenance on aluminum melting electric resistance furnaces and brass melting induction furnaces. Also sand casting and molding machines. Hell our vacuum for cleaning out the sand trench is on a dual axle trailer and is powered by a 150hp 660volt motor. It suck my boot off of my foot yesterday... That was not fun.
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Well, short update. When it rains it pours. Got the new starter on, was a spare off of my old blazers 4.3 so its a small body gear reduced model, so nice for sliding up in place.
Nice and quiet, the car fires right up. Also replaced the vac advance canister and it works properly now. The issue now is I couldn't fine the ported advance. Looked and looked for the fitting, and thought I was blind until I realized that the brass tube is missing. So when I get a minute I have to pull one out of a parts carb and install it. But, I have the idle dialed in pretty darn good now so now it's a waiting game for April when I can legally drive on the road to do the primary circuit.
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Are you saying the vacuum tube in the main casting for the spark advance is "missing"?
That would also be a vacuum leak at cruise, and would not only lean out the circuit it would suck unfiltered dirty air into the engine......Cliff
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Yes its missing. Just a hole, I never paid that close of attention before I replaced the vac can. I looks like I either was pulled out or vibrated out. But, I have a few donors carbs I can pull one out of. Assuming the are just press fit.
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It's just a press fit but if it doesn't fit tight put some loctite on it.