Quadrajet percolation. - Team Camaro Tech
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post #1 of 12 (permalink) Old Jun 30th, 09, 12:47 PM Thread Starter
Andreas
 
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Quadrajet percolation.

Hello all,
I have a huge problem with starting my car when hot outside, the symptoms is that the engine starts perfectly when cold and runs perfect forever, but when I shut it down itīs almost impossible to start it up again if it has sit for a couple of minutes (remember, only when hot outside)
I can sometimes get it to start if I hold the pedal to the floor....and when it finally starts it smokes black for a couple of seconds and then runs just as fine that it was before...
I have a totally stock 1969 350 engine (from a 1969 fullsize car, lika a Impala or similar) with stock iron intake and a Q-jet that is a little newer then the engine (1978, seriesnumber starts with 170, and the carb has been remanufactured by Holley, according to a small label on it) And also stock exhaust manifolds with the heat riser.
Things I have done/checked so far is: Insulated the fuel line from pump to carb, Checked that the heat riser is open. I even wired it open)
Removed the carb and epoxyed the known leaky plugs, and I have that extra thick gasket below the carb...
So what am I missing here, I mean these cars/engines didnīt came with this hickup when new so....is the fuel quality much worse know or what....
Do I need to put a wood/phenolic carb spacer on to solve this or is there supposed to be some kind of shield somewhere that I donīt have?
Any input is much appreciated...
Regards, Andreas. Sweden.

Camaro 1969 ProTouring, LS2/T56, Art Morrison Subframe, Chris Alston G-link.
Chevrolet Nova 2DR/HT 1967 (under construction)
Chevrolet Bel Air 1957
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post #2 of 12 (permalink) Old Jun 30th, 09, 01:06 PM
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Jim
 
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Re: Quadrajet percolation.

Andreas what ignition do you have? Points or converted to electronic ignition? My 350 with Qjet on cast iron intake, starts harder when cold from overnight, but even then starts in less than 10 seconds. When mine is warm, it pop's right off when I touch the key. I wonder if its an electronic issue?

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post #3 of 12 (permalink) Old Jun 30th, 09, 04:58 PM
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george
 
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Re: Quadrajet percolation.

Perhaps your a tad rich on the idle air/mixture.The hot engine will not fire off rich and burying the pedal introduces raw fuel from the accel pump and compounds the isssue.lean it out a tad with the mixture screws and see if this helps.

George
68 Camaro
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post #4 of 12 (permalink) Old Jun 30th, 09, 05:04 PM
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Re: Quadrajet percolation.

Definatley a flooding problem.

Misinformation Deleted since the OP has already address the plugs and thick gasket.

Is the choke set too rich. Electric chokes have a nasty reputation for cooling down and over choking a hot motor. If so you'll need to adjust the choke housing to point a couple notches closer to 'L'.

Dave
========================
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post #5 of 12 (permalink) Old Jun 30th, 09, 08:13 PM Thread Starter
Andreas
 
Join Date: Feb 2009
Location: Sweden
Posts: 18
Re: Quadrajet percolation.

I have stock points ignition, with the coil on the intake.
I donīt have an electronic choke.
One thing more I have checked is that I have a good spark when she doesnīt start....

Camaro 1969 ProTouring, LS2/T56, Art Morrison Subframe, Chris Alston G-link.
Chevrolet Nova 2DR/HT 1967 (under construction)
Chevrolet Bel Air 1957
Pontiac G8 GT 2009 (daily driver)
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post #6 of 12 (permalink) Old Jul 1st, 09, 09:31 AM
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Charlie
 
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Re: Quadrajet percolation.

Quote:
Originally Posted by Firehawk-Adde View Post
Hello all,
I have a huge problem with starting my car when hot outside, the symptoms is that the engine starts perfectly when cold and runs perfect forever, but when I shut it down itīs almost impossible to start it up again if it has sit for a couple of minutes (remember, only when hot outside)
I can sometimes get it to start if I hold the pedal to the floor....and when it finally starts it smokes black for a couple of seconds and then runs just as fine that it was before...
I have a totally stock 1969 350 engine (from a 1969 fullsize car, lika a Impala or similar) with stock iron intake and a Q-jet that is a little newer then the engine (1978, seriesnumber starts with 170, and the carb has been remanufactured by Holley, according to a small label on it) And also stock exhaust manifolds with the heat riser.
Things I have done/checked so far is: Insulated the fuel line from pump to carb, Checked that the heat riser is open. I even wired it open)
Removed the carb and epoxyed the known leaky plugs, and I have that extra thick gasket below the carb...
So what am I missing here, I mean these cars/engines didnīt came with this hickup when new so....is the fuel quality much worse know or what....
Do I need to put a wood/phenolic carb spacer on to solve this or is there supposed to be some kind of shield somewhere that I donīt have?
Any input is much appreciated...
Regards, Andreas. Sweden.

I had this exact issue and it was solved when I installed a phenloic(plastic) spacer under the carb. It has to be either plastic or wood. Aluminum will actually radiate heat and make it worse.

Charlie Knudsen 67 Camaro RS/SS 350 TKO 600, 4.10's, AFR 195 Street Heads, Comp 270H, Rhoads Lifters, Crane Ignition, Pertronix Dizzy, Performer RPM Q-Jet, Heavily Modified Q-Jet, Hooker Comp Headers, MagnaFlow 2 1/2", 144 Decibles(Alpine CDA-7998 Head Unit, RF X7 and RF 750X Amps, MB Quart Mid's & High's, Kicker L7 12" Solo Barics)
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post #7 of 12 (permalink) Old Jul 1st, 09, 09:33 AM
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Charlie
 
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Re: Quadrajet percolation.

Quote:
Originally Posted by fatblock View Post
Perhaps your a tad rich on the idle air/mixture.The hot engine will not fire off rich and burying the pedal introduces raw fuel from the accel pump and compounds the isssue.lean it out a tad with the mixture screws and see if this helps.

Actually the way to help a flooded motor is to push the pedal to the floor and hold it there. DO NOT pump the pedal, simply push and hold. This opens the butterflies and allows fresh air to enter and push all the fuel out.

Charlie Knudsen 67 Camaro RS/SS 350 TKO 600, 4.10's, AFR 195 Street Heads, Comp 270H, Rhoads Lifters, Crane Ignition, Pertronix Dizzy, Performer RPM Q-Jet, Heavily Modified Q-Jet, Hooker Comp Headers, MagnaFlow 2 1/2", 144 Decibles(Alpine CDA-7998 Head Unit, RF X7 and RF 750X Amps, MB Quart Mid's & High's, Kicker L7 12" Solo Barics)
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post #8 of 12 (permalink) Old Jul 1st, 09, 09:34 AM
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Charlie
 
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Re: Quadrajet percolation.

The next time you try to start it when it's hot, push the pedal to the floor and hold it there. Then try to start it. If it's percolation, you should be able to get her to fire without having to let her sit by HOLDING the pedal to the floor. Whatever you do, DO NOT pump the pedal!!! The earlier Q-Jets had a valve in the rear of the carb that aided it in starting for just this purpose. Why they did away with it, I'll never know.

Charlie Knudsen 67 Camaro RS/SS 350 TKO 600, 4.10's, AFR 195 Street Heads, Comp 270H, Rhoads Lifters, Crane Ignition, Pertronix Dizzy, Performer RPM Q-Jet, Heavily Modified Q-Jet, Hooker Comp Headers, MagnaFlow 2 1/2", 144 Decibles(Alpine CDA-7998 Head Unit, RF X7 and RF 750X Amps, MB Quart Mid's & High's, Kicker L7 12" Solo Barics)
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post #9 of 12 (permalink) Old Jul 1st, 09, 05:10 PM
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george
 
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Re: Quadrajet percolation.

Quote:
Originally Posted by 67CamaroRS/SS View Post
Actually the way to help a flooded motor is to push the pedal to the floor and hold it there. DO NOT pump the pedal, simply push and hold. This opens the butterflies and allows fresh air to enter and push all the fuel out.
I doubt many would disagree..myself included.Its simply a bandaid to cover up the underlying issue as to why it is rich on a hot restart.For the few seconds it takes for a test..I would still lean out the idle/air fuel ratio a tad with the mixture screws.
If you do have to floor the pedal to clear flood...move the pedal very slowly to the floor before cranking.This will not introduce as much raw fuel pump shot as compared to just mashing it.Watch your shooters from atop at rest and you will see the difference in delivery.You can all but go to wot with only a dribble out the discharge nozzles.

George
68 Camaro
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post #10 of 12 (permalink) Old Jul 1st, 09, 06:21 PM
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Jon
 
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Re: Quadrajet percolation.

FWIW, in late 85 GM went to a slightly thicker gasket between the base plate and the float bowl to help prevent some of the percolation you are seeing. If this is a summer time only car, you might get away with blocking off the heat crossover passage under the intake manifold. You may be able to do it with out removing the intake. I have loosened all the intake bolts, then slipped thin stainless steel shims into that area of the gasket and then retightened the bolts. What can you lose?

Jon N

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post #11 of 12 (permalink) Old Jul 2nd, 09, 09:05 AM
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Charlie
 
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Re: Quadrajet percolation.

I would try installing a 1/2" phenolic spacer. Not only will it assist you with your hot restart, but if you use a 4 hole spacer, you will pick up low end torque. Consequently, if you use an open spacer, you will gain top end horsepower.

Charlie Knudsen 67 Camaro RS/SS 350 TKO 600, 4.10's, AFR 195 Street Heads, Comp 270H, Rhoads Lifters, Crane Ignition, Pertronix Dizzy, Performer RPM Q-Jet, Heavily Modified Q-Jet, Hooker Comp Headers, MagnaFlow 2 1/2", 144 Decibles(Alpine CDA-7998 Head Unit, RF X7 and RF 750X Amps, MB Quart Mid's & High's, Kicker L7 12" Solo Barics)
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post #12 of 12 (permalink) Old Jul 2nd, 09, 09:06 AM
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Charlie
 
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Re: Quadrajet percolation.

Quote:
Originally Posted by fatblock View Post
I doubt many would disagree..myself included.Its simply a bandaid to cover up the underlying issue as to why it is rich on a hot restart.For the few seconds it takes for a test..I would still lean out the idle/air fuel ratio a tad with the mixture screws.
If you do have to floor the pedal to clear flood...move the pedal very slowly to the floor before cranking.This will not introduce as much raw fuel pump shot as compared to just mashing it.Watch your shooters from atop at rest and you will see the difference in delivery.You can all but go to wot with only a dribble out the discharge nozzles.

I agree that it's a temp. fix, but if the need to hold the pedal to the floor is present, it indicates a fuel percolation issue that can be remedied with a phenolic or plastic spacer, IMO.

Charlie Knudsen 67 Camaro RS/SS 350 TKO 600, 4.10's, AFR 195 Street Heads, Comp 270H, Rhoads Lifters, Crane Ignition, Pertronix Dizzy, Performer RPM Q-Jet, Heavily Modified Q-Jet, Hooker Comp Headers, MagnaFlow 2 1/2", 144 Decibles(Alpine CDA-7998 Head Unit, RF X7 and RF 750X Amps, MB Quart Mid's & High's, Kicker L7 12" Solo Barics)
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