Cliff's Quadrajet Parts and Rebuild Kits
Quadrajet Problem Solving => Dialing in your rebuilt Quadrajet carburetor => Topic started by: defiant1 on May 31, 2011, 06:38:30 PM
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Need to know the proper procedure to set up the idle and subsequent adjustments on the 17080204 Q-jet.
Background:
Sent carb to have throttle shafts redone via Cliff
Purchased rebuild kit from Cliff
Oh, and bought Cliff's book
APT plug was removed and set screw installed
Carb specs:
#17080204
Idle Tube: .036" (I believe this is correct unfortunately I forgot to measure before install and Cliff's packages don't come labeled)
Idle Down Channel: .055"
Upper Idle Air Bleed: .070"
Lower Idle Air Bleed: .068"
Idle Bypass Air: .081"
Mixture Air Screw Holes: .096"
Float Height: 5/16"
APT screw: 4 turns from seated
Main Jets: #73
Secondary Rods: CH
Secondary Metering Rods: #44
Idle Mixture Screws: 4 turns out from seated
Motor Specs:
SBO 350
Rebuilt Cylinder Heads
9.0:1 CR
Cam Specs:
LSA: 108 +2 (Installed straight up)
Duration: 217/224
Rocker Arm Ratio: 1.6:1
Ignition:
Pertronix III with Flamethrower Coil
I installed heavy mechanical advance springs in the distributor.
Spark Plug Gap: .042
Ok-I don't have any documentation on how to set the idle (either curb or fast idle).
The electric choke works well--I was concerned as I have never used one.
The motor starts on the first turn of key. All I have to do to push accelerator pedal down once. (I know, I know, like its suppose to-- but when you have never had that in a carb before it is a welcomed change)
The motor runs smooth at higher rpm but at idle it shakes like I got bad motor mounts (mounts are new).
It runs a little rich based on what the plugs look like.
I did the "tip in" procedure and there was no change in rpm.
So before I start turning screws randomly, I am looking for the procedures to set the idle scews and make adjustments from there to remedy the rough idle.
Thanks
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Vacuun gauge and an RPM gauge. Id set the initial at 12 to start with. Youll be looking for the highest vacuum reading at the appropriate idle RPM . You can get the gauges at sears or auto zone. you may nees to go back and forth with the adjustment cause adjusting your mixture may effect the rpm to go higher. so you gotta adjust the rpm speed back down, then go back with the mixture adjustment and etc.
over and over til its just right. Ill bet it will smooth right out.
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Where am I pulling vacuum from (carb, manifold)? Also is 12 the vacuum reading or the initial timing you mentioned I start with??
Is there a chart that correlates RPM with vacuum?
Thanks
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...sorry for confusion. 12 would be the timing advance setting while the engine is idling. (with distributer vac advance disconnected; plug the vac line). this is just a base to start with and really just a guesstimate but for your engine combo. Use a manifold vacuum source with your vacuum gauge to set your idle mixture. As far as a correlation of rpm to vacuum, that would be impossible to do because every engine is different. The engine will make whatever vacuum it wants to. this goes for any engine. Even engines that are identicle from the factory will vary! they'll be close but not identicle. Your job while setting the idle mixture is to obtain the highest vacuum that you can (observed on the gauge) while maintaining a predetermined rpm (some engines with big cams do not like to idle at a slow speed). My old pontiac 350 liketo idle at about 650 rpm. this was aparantly the factory specification for the idle speed for this engine equipped with an auto trans. At this speed it made 18 inches of vacuum. (extremely good reading for a 40 year old engine and that had never been rebuilt) Idle speeds are set after teh engine has warmed up to operating temp. If you look in a chiltons book or similar, it will give yu the specification for the idle speed for STOCK engines from the factory. So, you want to keep theidle as slow as practible for reduced wear, emissions , fuel consumption, drivetrain wear etc. BUT, you do not want it to be too slow or it will stall out, be impossible to set mixtures, and the alternator needs some rpms to make voltage and other various things. So you need to figure out at what speed you want it to idle because of the modifications to the engine such as the cam. You will git an idea of what you think you can live with when you start to do the tuning. The idea is to get the highest vacuun reading you can at the lowest rpm that are PRACTICLE for you engine. Guys with very good skills at setting up the idle circuit can get their cars to idle at a lower speed and still pull decent vacuum. what you are actually doing is finding the optimum burn in the cylinder and the 2 things it boils down to is ignition timing and mixture quality.
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Ok-still working on getting a vacuum gauge.
In the meantime, I turned in the idle mixture screws in all the way and the motor rpm did not change.
The carb sounds like it is pulling vacuum hard (very noisy). I don't want to spray carb cleaner on the intake manifold due to new paint. I have a 1" phenolic spacer. Could the gasket in between bottom of the carb and top of the spacer be the problem?
I will still check vacuum after I get the gauge.
d1
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I think I would do this; check for a vac leak that might be a vacuum hose, it kinda sounds like you problem..Also, if the idle mixture needles are not seating all the way, the spring on them may be at coil bind. You may need to trim a coil or two from them. You shoukd be able to kill the engine with the turning in of the idle screws. Of course, you wont get a super smooth idle with the cam you have but it should be close to a factory performance cam, pretty smooth in the case of an olds. As far as the gasket goes, yes this may have a vacuum leak but unless you can check for a leak....in the old days, I used to use an unlit propane torch to check for leaks but everyone seem to think it is dangerous. I guess maybe but the only other way I know of is some type of spray. Another guy I know says he sprays water to check for leaks. I have never tried it but who knows. Dont forget to check the timing and you should have 12 at idle, (vac. adv. disconecttd.) Try 14 degrees and see if it helps, if not, put it back. check plug wires too, firing order and connections. If the spacer is good quality, it should work. But, you might try it without the spacer just to see if it makes a difference.
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Ok - update:
- Can't install carb without spacer, due to throttle linkage hitting intake. So could not attempt that setup.
- Installed different gaskets (thicker base gasket).
- 10* at 1100 rpm for timing based on what the manual is telling me to set it at.
- Vacuum gauge read 10.5" at 700-750 rpm. 18 inches @ 2000 rpm. No idea what that means in the large scheme of things.
- Idle mixtures screws DO now affect rpm when screwed in, whereas before they did not. So I am gaining there, I think.
I am going to do a compression test on the cylinders and see what I come up with.
Forgot to add: I used a stronger power piston spring. It was the same length as the factory spring, but there were more coils (if that makes any sense), basically a stronger spring. Should I put the factory or replacement equivalent in and see if that helps with the idle. Of course this is assuming the vacuum numbers listed above are ok.
d1
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Make sure the flaps are closing all the way. Work them a little and push them closed as you run it to see if they are not fitting tight or closing 100%.
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Not sure what you mean by moving the flaps or attempting to move them. Can you elaborate? Side to side movement of throttles shaft??
Well I did the following this afternoon:
BTW: I have the Petronix III unit with flamethrower coil. I ran this setup with my former 2BBL/intake (same motor w/o head work) at 10* BTDC at 1100 rpm (dist. vacuum capped off).
I just finished my compression test, ran motor to operating temp and took readings:
#1 - 159
#3 - 155
#5 - 155
#7 - 162
#2 - 157
#4 - 159
#6 - 163
#8 - 160
Not too bad for a 40 yr motor with no work done to the bottom end.
I also checked the plugs and the #1 plug was the worst looking-had a black coat on the ceramic. The remaining plugs had a light to dark brown ceramic coating. Nothing was covered in soot.
When motor was running I got brave and squirted starting fluid around base of carb. No noticeable difference in rpm occurred.
The local mechanic thought the vacuum was pulling from w/in the carb itself. If that is the case I have no idea what circuit inside the carb controls that. BTW I had every vacuum port plugged with the exception of the PVC and the power brake hose which I used to hook up my gauge.
I noticed this time around my idle Hg reading at 750 was a steady 11".
I thought I had fixed my idle mixture screw problem, but I screwed them in all the way and the idle did not change (well maybe 50 rpm--but it should have made a noticeable difference).
New items:
4BBL Q-jet
Cam: custom grind 217/224 @.050
Edelbrock Performer intake
I am open to suggestions.
d1
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Ok- trying to eliminate things that could cause problem. I took a skinny screwdriver and placed it in the vent tube to ensure the power piston goes up and down (motor off).
With motor on, I did the same thing and the power piston is fully seated. So the light blue spring I am using is not affecting the idle circuit from what I can tell.
Adjusting the idle mixture screws in or out does little to nothing to the RPM.
I am out of ideas.
- 10.5" Hg at 750 rpm - not sure if that is good or bad
- Idle does not improve when I cup my hand over primaries
- Sprayed starting fluid around carb and rpm did not increase
What else can keep the idle mixture screws from doing their job??? ???
d1
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If you have chenged the cam to one that is larger, you will need more initial advance. I would try 14 or 15 degrees initial advance. Also, the idles RPM speed ay end up a little bit higher. Since this cam is something that is new, it changes the parameters of the engine characteristics. The only other thing that I can think of would be the idle tubes not being large enough but it seems like this would be not the case.
What is the exact advertised duration of this cam? (the specs yu gave are duration at .050 lift I assume).
The 108 centerline is just a bit tighter than most of the cams out today that are made with 110. This small amount more overlap may be causing some of the issues with the idling. The vac reading sure seems a bit low. I would expect ~12-14 inches with a 217/224 @ .050 cam but what is the advertised duration? Bump the initial timing to 14 or 15 at Idle. try to stay below 1000 rpm when setting the initial timing. (although you can tell when it starts to advance with the timing light.)
Just trying to get an idea of what cam you have to figure out what you can expect with the idle quality. Some cam will make the engine shake a bit.
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The camshaft is a custom grind. Erson Cam- 268/284 LSA: 108+2 Valve lift: intake-.494 exhaust-.504 Overlap: 60
Intake center line: 106 @ .050
I degreed the cam and verified all the specs.
When I get home tonight I will try the 14-15* at lets say 900 rpm and go from there.
Is there a correlation between how far the throttle plates are open and the Q-jet's idle circuit when the motor is at idle?
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I meant the Secondary Flaps. On mine I had trouble initially getting the idle mixture to respond to the screws. THe flaps were not closing by the smallest bit. They needed some "working" open / close - open /close etc.
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Ok- tonight I retorqued my intake manifold.
I plugged off both valve cover grommets and left the hose for the PCV attached to carb and left the other end open.
I started motor and it was pulling a steady 11" vacuum with hose open. When I put my finger over the hose and plugged it the vacuum jumped to a steady 15". Not sure what this exactly means but just an observation.
Ok hooked up everything else back up and ran motor. Set the timing at 14* at 850 rpm. The vacuum at this setting is a steady 12.5". I played with the timing up and down for awhile and this seemed to be the happy medium. The motor has an occasional slight even shudder at times but it was not abrupt. Although a shudder to me still screams vacuum leak...so still not sure.
It would run rougher when I turned in the idle mixture screw all the way in, but still would not kill the motor or make a substantial decrease in rpm.
It dieseled a little when I shut it down. But I guess this could be attributed to making multiple adjustments to the timing.
I might be gaining, but still not completely confident I got the idle figured out.
On another note: Does it matter what port on the carb (Chevy Q-jet) I hook the PCV hose to? I am using the one in the front on the baseplate, it that right? I plugged the rear port and am using the intake manifold for the power booster.
d1
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I was referred to another carb builder, I explained the issues I was having and he suggested the throttle plates were open slightly interrupting the idle circuit.
He said this would contribute to the following issues:
Low vacuum
Idle mixture screws having no affect
He suggested I:
Replace the power piston spring with the lightest spring to help keep to ensure the needle stays seated
Ensure that the throttle plates are covering from the middle to lower third of the transition slots (vertical slots in bore).
Idle Bypass Air hole should be drilled a little larger. Mine is .081" He recommended .093" I will drill the hole incrementally until it runs the best.
And verify that fuel is not dripping from nozzle
I will make these mods and see what happens.
d1
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Made some adjustments:
Drilled out the idle air bypass to .086 from .081.
Installed lighter power piston spring.
Adjusted throttle plates so no more than .040 of the transition slots was showing.
Hooked everything back up. Ran motor to operating temp and kicked it off of the choke. It died. So I attempted to hold the throttle at a steady rpm and adjust the timing at the same time. Could not get it to idle. Wound up turning the throttle screw in 1 1/2 turns.
Idle mixture screws were set 5 turns out from seated.
It ran ok (still shuddered) at 850 rpm/14* BTDC and held 12" Hg for vacuum.
However, do to the fact I adjusted the throttle plates 1 1/2 turns I am sure I am no where near the .040" I originally set it at.
Oh then I leaned over the fender and looked down the carb. It looks like I have nozzle drip as well at idle.
Soooo, do I increase the Idle Air Bypass hole diameter even more? Do I back off the idle mixture screws even more? I am gaining. Vacuum is a little better, motor runs a little more consistent...rough idle but consistent.
How do I rectify the nozzle drip? I am assuming this is happening because the throttle plates are open too far at idle.
If that is the case, how can I get the motor running effectively with throttle plates nearly closed???
d1
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It seems like you are getting a lot of good help from others but I thought that I would ask a question and make a couple of observations. For an engine to jump 4" of vacuum when you removed the PCV valve, that seems like a lot. Have you checked to make sure your PCV valve is the correct one for the engine? I ask because I had this issue in the past where the PCV was not calibrated properly for the engine and it was allowing too much air. If I am correct in that it is allowing too much air, this would explain why your idle screws are not making much of a difference because it is so lean.
When you plugged the PCV hose, I am going to assume that it idled much better since the vacuum jumped to 15". Is this correct?
If you add more bypass air, I think it will only make your issue worse. The way it is now, you have had to open the throttle plates so that it would get some fuel out of the main system to keep running. Closing the throttle plates enough to stop the drip reduces the fuel but if the system is as lean as it sounds, then it won't idle.
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I have a new PCV valve coming (just in case). I just ordered one that is for my motor Olds 350, are there different versions out there that compensate for camshafts, timing, etc.??
It did run better when I plugged the hose, rpm increased almost 500 rpm from where it was at so I guess it was not really at idle at that point.
I have not mentioned this yet, but is my APT screw (I can access it) preventing the idle circuit from working correctly? It is 4 turns out from seated, so this prevents the power piston from traveling all the way down. When I had it apart I noticed the metering rods could travel quite a bit farther when the APT was seated. Or does the jet/primary metering rods not affect the idle circuit??
Thanks for the feedback. Trying to get this figured out before summer is over. >:(
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Drill out the IAB to .096. Idle mixture screw 9 1/2 turns out--I started out at 5 and the more I turned it out the less nozzle drip I had. Decreased my nozzle trip by 2/3. Before it was gushing out, now it is a drip. Throttle screw still turned over 1 full rotation to get to run at idle. I am still assuming the throttle blades are open too far leading to the nozzle drip.
Any other suggestions. Vacuum is around 12.5" I am slowly improving this reading with every adjustment I make.
d1
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Looking at the engine combination, it's going to need more idle fuel to the mixtures screws, and more idle bypass air. That's a "hefty" cam in a 350 engine at that compression ratio. Is the cam ground on a 108 LSA (Lobe Separation Angle), or is ground on a 112LSA and installed at 108 ICL (Intake Center Line)?......Cliff
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Looking at the engine combination, it's going to need more idle fuel to the mixtures screws, and more idle bypass air. That's a "hefty" cam in a 350 engine at that compression ratio. Is the cam ground on a 108 LSA (Lobe Separation Angle), or is ground on a 112LSA and installed at 108 ICL (Intake Center Line)?......Cliff
Not sure, let me ask the vendor. All the data sheet says is 106 ICL @ .050 tappet rise. LSA: 108+2
Shaun
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yeah, I agree with the PCV issue. the pcv should not drop that much. THat cam is bigger than I expected and yeah, if it has tight lobes like 106 for example, it will idle somewhat rough and need more idle fuel. LSA means lobe separation angle, and is how "tight" the intake lobe is in comparison to the exhaust lobe. You must find out how tight the cam is. The installed centerline refers to where the cam is installed by using the lobe center of the intake as a reference. Tight lobe seperation cam will idle a bit rough due to the increased overlap however, it will retain more cylinder pressure (just comparitivley speaking of course) because of the earlier closing intake valve so it could actually be a good coice for a 350 cube engine where comprerssion is a bit harder to make than a large cube engine.
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Looking at the engine combination, it's going to need more idle fuel to the mixtures screws, and more idle bypass air. That's a "hefty" cam in a 350 engine at that compression ratio. Is the cam ground on a 108 LSA (Lobe Separation Angle), or is ground on a 112LSA and installed at 108 ICL (Intake Center Line)?......Cliff
Back from vacation (visited Mt. Rushmore, I highly recommend the Black Hills if you have not been). At any rate, Cliff, the vendor said the cam was ground based off the 108 LSA and it is installed at 106 ICL. What other adjustments do I need to make to the carb to get it to idle right. I got a parade on July 4th and need to have the car up and running before then.
d1
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108LSA is not helping the situation. I'd go bigger on the idle tubes, .038 or even .039", .058" down channel restrictions, and .110" idle bypass air. It needs more idle fuel and some help getting back on the idle curcuit.
Don't rule out timing either, it may need more initial timing to be happy. I just cured idle troubles with a Buick 350 yesterday, by adding idle fuel, and recurving the distrbutor for more timing at idle speed.....Cliff
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108LSA is not helping the situation. I'd go bigger on the idle tubes, .038 or even .039", .058" down channel restrictions, and .110" idle bypass air. It needs more idle fuel and some help getting back on the idle curcuit.
Don't rule out timing either, it may need more initial timing to be happy. I just cured idle troubles with a Buick 350 yesterday, by adding idle fuel, and recurving the distrbutor for more timing at idle speed.....Cliff
Thanks Cliff, I will order the parts from you tomorrow.
Shaun
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108LSA is not helping the situation. I'd go bigger on the idle tubes, .038 or even .039", .058" down channel restrictions, and .110" idle bypass air. It needs more idle fuel and some help getting back on the idle curcuit.
Don't rule out timing either, it may need more initial timing to be happy. I just cured idle troubles with a Buick 350 yesterday, by adding idle fuel, and recurving the distrbutor for more timing at idle speed.....Cliff
Ok- Idle tubes replaced w/.039 Idle channel opened to .059 and Idle Bypass air was drilled out to .110"
I am still having the same problem. Engine runs great at fast idle (great vacuum, etc.) as soon as I kick it off the choke circuit it starts spurting fuel out of the nozzles. Backing off the mixtures screws again starts to decrease the nozzle drip, but it does not stop it completely.
Need to some more ideas folks. This is insane. I have a lot of time and money in this carb and I am not happy >:(
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Have you replaced that PCV valve? (I would block that off for now, just plug the hose for now). The reason I am saying is because you said that when you did this before, you had 15 inches of vacuum.
I would also bump the timing up to 15 or 18. You should able to get it to idle with the 15 inches of vacuum. and the timing at 15. Im really thinkin now that this maight be the problem (the pcv). It will idle its just a matter of the timing and the mixture. Those are the only 2 things. Dont forget, that vacuum gauge can be used as a tool to figure out where the initial timing wants to be set at. since the most efficient burn ( timing and mixture again) will cause the highest vacuum reading, this is why the vacuum gauge is one of the best tools for determining where everything needs to be set at because the timing and the mixture quality will both effect the vacuum reading. keep experimenting with the timing and the mixture and watch the vacuum gauge. Of course, you can go too far with the initial timing and cause the engine to not start up easy with the starter and maybe have some pinging while driving, in that case yull need to back off the timing a bit. with the pcv, its possibe that it is not operating correctly with the cam that you have (because of the pulses of the vacuum or not enough vac etc.) You may end up with a higher idle rpm also just to get it to idle but not excessive amount extra I would not think. It shoukd idle with the .039 and the .059 idle system. Dont get too frustrated and do not give up. (my .02)
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The current set-up should have plenty of idle fuel. Might want to raise the float to 1/4" instead of 5/16". That will add a tad more fuel to the idle system.
From the sounds of things, the engine isn't very happy with that cam in it. I've seen a lot of idle issues with small/low compression engines using tight LSA camshafts.
It wants timing and idle fuel, you are going to have to give it what it wants to be happy at idle speed. If the engine had another point of compression in it, it would be fine with the current settings....IMHO.....Cliff
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Have you replaced that PCV valve? (I would block that off for now, just plug the hose for now). The reason I am saying is because you said that when you did this before, you had 15 inches of vacuum.
I would also bump the timing up to 15 or 18. You should able to get it to idle with the 15 inches of vacuum. and the timing at 15. Im really thinkin now that this maight be the problem (the pcv). It will idle its just a matter of the timing and the mixture. Those are the only 2 things. Dont forget, that vacuum gauge can be used as a tool to figure out where the initial timing wants to be set at. You may end up with a higher idle rpm also just to get it to idle but not excessive amount extra I would not think.
I did reaplace the PCV valve, but I will try it plugged and see what happens. I changed float height to 15/32" and tried again. Got it to run ok at 880-900 rpm @ 19* BTDC. It is not dripping fuel at a rapid rate like before, it is just barely weeping out, if you weren't using a flashlight you would not be able to see it.
But, if no fuel is suppose to be coming out at all, then not sure what is left. I guess I could open up the idle tubes more??
I will take a look at the vacuum readings next time and see where the best adjustment is. At initia startup while it is on the choke at around 1000 rpm it is pulling 15", but as soon as it it gets off fast idle it drops around 12".
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OK- Omaha I think you are on to something. I plugged up the port on the carb that goes to the PCV valve. Ran the motor to operating temp. Timing is 14* at 850 and was pulling 14-15" of vacuum. Motor ran really consistent and was not shuddering (very very minor shuddering if at all).
I hooked up the PCV valve again leaving the timing and RPMs the same and it ran like ass. Shuddered horribly and the vacuum dropped to 11"
Soooooo, since I replaced the PCV valve twice. 1. Why is this happening? 2. Is there another way to achieve crankcase ventilation so I don't hurt the motor? 3. Are there custom PCV valves? 4. Can I install a breather on the oil fill tube, similar to the Olds 425 motor I received recently which does not have any PCV valve or breather on the valve covers, only a vented oil fill cap.
Thanks for sticking with me on this.
d1
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Well, think of it this way. All a pcv valve consists of is a spring, a ball and a bypass passage. Oldsmobiles were noted for there smooth operation which, was attributed to their camtiming, timing, etc,etc. From the factory, they made alot of vacuum, maybe 18 to 20 inches sometimes. So they had a PCV valve that went along with this, it matched the engines vacuum. Now you have a cam that has lowered this reading so the PCV does not function correctly. (or maybe functioning intermittently) Maybe the vacuum is not enough to overcome the spring or close the passage or maybe the narrow cam is causing pulses in the intake (whatever). So basically, now you have an open large vacuum line, not a good idea if you want a good signal for a good idle quality.
No, you do not need the PCV and you can run the setup that is sold through summit that has the oil collection resevoir (you empty it once in a while). It is like a breather that works through a hose and collexts excess oil so it does not make a mess. Alot of guys running Big block chevies with big cams cannot run a pcv either. many racers dont either.
I will try and find the actual name of the deal that I am trying to explain.
Again, make good use of that vacuum gauge. Anything you can do to increas the vacuum is a step in the right direction with what you have.
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No, you do not need the PCV and you can run the setup that is sold through summit that has the oil collection resevoir (you empty it once in a while). It is like a breather that works through a hose and collexts excess oil so it does not make a mess. Alot of guys running Big block chevies with big cams cannot run a pcv either. many racers dont either.
I will try and find the actual name of the deal that I am trying to explain.
Again, make good use of that vacuum gauge. Anything you can do to increas the vacuum is a step in the right direction with what you have.
So does the canister suck the vapors out of the crankcase and still allow me to keep a high level of vacuum? Just don't want to spend money on something and not gain anything.
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Cliff,
Can the gasket between the base plate and main body of the carb affect the vacuum?? Had someone tell me this based on the fact that there was an issue when the PCV was hooked up to the port on the base plate.
Are there different gaskets for this application or are they all the same??
d1
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The carburetor throttle body is designed so that any PCV or power brake port will use vacuum from both sides of the intake manifold, no matter which gasket is used under it.
There may be some idle quality differences by using an open gasket on a fully divided intake, vs a 4 hole gasket, but the difference would be minimal.....Cliff
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Are there custom PCV valves?
I was aware of the PCV affect on the system by way of reading and talking to guys. So when the time came, to put in the PCV, I asked for a PCV for a 1970 455 GTO. I figured that a PCV designed for a big cammed 455 from the factory might be appropriate in my car.
I'm driving a '75 Formula powered by my homebuilt 455. Engine doesn't suck any oil and I don't have any evidence of a "vacuum Leak" type of situation. Smooth Qjet idle at about 750 in gear when warm. 11" - 12" of Vacuum.
I am currently running a .510 lift cam with a 110 LSA.
You can read and see talk of people using different PCVs dependent on the CAM and setup. So it makes sense that PCVS are sprung differently and the flow is different depending on the car.
"The biggest difference between valves is the orifice size through the center of the valve which determines flow when the vacuum is fairly low. It has to be balanced between too big (essentially a vacuum leak) to too small (which means no flow through the crankcase).
Factory PCV valves will have varying orifice size with engine size and camshaft specs. If you have a big cam, get a PCV valve for an engine that has a fairly radical factory cam. some say vacuum is highest at idle. That is not always true. Vacuum will pick up at higher engine speeds as long as the load is low, like cruising. It's highest when you are decelerating."
Here is some info on PCV's. http://www.aa1car.com/library/pcv.htm
(http://www.aa1car.com/library/pcv.gif)
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Good info on the PCV valve above.
Update to my situation:
Well I tried just installing 2 breathers and I had a lot of blow by. So, I installed 1 breather passenger side and one breather with a tube on the drivers side. I installed the PCV valve in line between base of carb and breather w/tube.
Instead of focusing on initial timing I set the timing based on mechanical advance. I set it at 33 degress all in before 3100 rpm. I checked my initial timing at this point and was at 13* @ 1100 rpm. It did not want to idle well at this point. So, I increased the timing to 15* and adjusted the fast idle and idle mixtures screw accordingly. So now I am at 35* all in before 3100 rpm. The only thing I don't know is the vacuum reading at this setting (still working on installing a permanent vacuum gauge).
Oh, and I wound up using the stock mechanical advance springs (sort of heavy-but not as heavy as the after market ones) and the aftermarket mechanical weights.
It runs the best at this setting, I still have an erratic idle while in drive with brake depressed and also while going reverse at slow speed. It idles around 750 rpm while in drive or reverse.
So I will keep tinkering with idle mixture screws and the throttle flaps.
d1
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I am still trying to figure this carb out >:(
Pulled the plugs and they are very white, indicating a lean condition. The plugs have over 300 miles on them. What can I adjust to rectify this issue? What setting needs to change to richen up the mixture?
I am still having idle issues, but no nozzle drip. Which is good I guess.
d1