Carb Problems
Thread Starter
7th Gear
Joined: Aug 2012
Posts: 7
Likes: 0
Carb Problems
I have a 1969 Corvette L36 427 390hp. The engine is a numbers matching to the vin of the car. I am new to the Corvette world so I need some help!
I live in Calgary Alberta Canada at about 3300 feet above see level. I took the car out and my first impression was it was starving for fuel. I changed the fuel filter at the carb and checked the in line fuel filter. The in line filter seemed fine as air passed through it freely. I changed the points over to Electronic Ignition. I went with the under the cap model to keep the OEM look. I changed the plugs and noticed 1through 4 plugs were burt way worse than 5 through 8? After these minor repairs were done I took the car out again and the problem was still there. Seems to idel fine but as soon as I kick it down it bogs and seems to choke itself. The four barrels are not opening up. Its a Quadrajet but I dont think its original factory? Should I just replace the carb and see if that fixes the problem or is there a better option?
Thanks!
PS LOVE the car! A real dream to drive and what a head turner!!!
Cheers!
I live in Calgary Alberta Canada at about 3300 feet above see level. I took the car out and my first impression was it was starving for fuel. I changed the fuel filter at the carb and checked the in line fuel filter. The in line filter seemed fine as air passed through it freely. I changed the points over to Electronic Ignition. I went with the under the cap model to keep the OEM look. I changed the plugs and noticed 1through 4 plugs were burt way worse than 5 through 8? After these minor repairs were done I took the car out again and the problem was still there. Seems to idel fine but as soon as I kick it down it bogs and seems to choke itself. The four barrels are not opening up. Its a Quadrajet but I dont think its original factory? Should I just replace the carb and see if that fixes the problem or is there a better option?
Thanks!
PS LOVE the car! A real dream to drive and what a head turner!!!
Cheers!
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,112
From: Crossville TN
If it still has the Q-Jet carb on it and the car not originally configured for that altitude, you may need some adjustments of rods/jets/power piston spring for it to get the air/fuel mixture adjusted better. And, with a car of such age, lots of other fuel-related and/or ignition-related issues can arise which might cause such problems.
I'm not certain, but I think your intake manifold is a dual-plane design. And, if it is, one side of your carb may be producing a different air/fuel mix ratio than the other. You might have a clogged metering jet or a damaged metering rod, for example.
If I were you, I would send Lars Grimsrud an e-mail stating the problems you are having and ask for his help in advising me of possible problem areas for me to check into. You can contact him at V8FastCars@msn.com. He will not respond to PM's/twitter/facebook or any of the other "tech" methods of communication. Good luck.
I'm not certain, but I think your intake manifold is a dual-plane design. And, if it is, one side of your carb may be producing a different air/fuel mix ratio than the other. You might have a clogged metering jet or a damaged metering rod, for example.
If I were you, I would send Lars Grimsrud an e-mail stating the problems you are having and ask for his help in advising me of possible problem areas for me to check into. You can contact him at V8FastCars@msn.com. He will not respond to PM's/twitter/facebook or any of the other "tech" methods of communication. Good luck.
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,170
From: Hermosa
sounds like carb issues. The q-jet can be made to run excellent. It takes some effort to do so and maybe a complete rebuild.
I highly recommend this book even if you don't rebuild the entire carb it gives you great insight to the function of the q-jet.
http://www.amazon.com/Rebuild-Modify...6126667&sr=1-1
I had similar problems with my 77 when I first owned it. rebuilt the carb via Cliff's book and now it runs like it is fuel injected. I also live at a higher elevation. 3500 feet to 6000 feet is where I usually operate it.
I highly recommend this book even if you don't rebuild the entire carb it gives you great insight to the function of the q-jet.
http://www.amazon.com/Rebuild-Modify...6126667&sr=1-1
I had similar problems with my 77 when I first owned it. rebuilt the carb via Cliff's book and now it runs like it is fuel injected. I also live at a higher elevation. 3500 feet to 6000 feet is where I usually operate it.
Burning Brakes
Joined: Dec 2010
Posts: 848
Likes: 60
From: CA
The 7029207 is a 69 Corvette 350/350 (L46) with manual transmission carb. You should have the 7029204 if you have an automatic transmission. If it's a manual, you should have the 7029215.
And yes, contact Lars. He's the man in the know for carb issues.
Ed
And yes, contact Lars. He's the man in the know for carb issues.
Ed
Racer
Joined: Nov 2005
Posts: 340
Likes: 0
From: Dublin
I also had another contributing factor my air cleaner didn't have enough clearance.
Last edited by briaineo; Aug 28, 2012 at 11:37 AM.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,112
From: Crossville TN
Acutally, the '69 Corvette 427/manual carb should be a 7029201, I believe. And, other than some minor hardware differences in the side linkage (auto vs. manual), there's not much difference between the "correct" carb and what you have now. That is, if your carb was rebuilt to original specifications. You should just rebuild what you have, IMO. You need to find the 'problem' when you rebuild it; but, if rebuilt properly, it should be as good...or better...than the one that came from the factory.
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Burning Brakes
Joined: Dec 2010
Posts: 848
Likes: 60
From: CA
Actually, the '69 Corvette 427/manual carb should be a 7029201, I believe.
7029201 is listed in the CBTN for the 1969 Chevelle 396/325 (manual transmission), 1969 Camaro 396/325 (manual transmission), 1969 full size 427/335 (manual transmission) and possibly the early 1969 full size 427/390 (manual transmission).
The 1969 Corvette 427/390 is listed in both the CBTN and the Guidebook as having the 7029204 (automatic transmission) or 7029215 (manual transmission).
Ed
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,112
From: Crossville TN
My info shows that the 7029215 is for 69 CHEV 396/427 M/T. The 7029201 is for Chev 69 CAMARO, VETTE 396/427 M/T. When you check the detail items, the only difference between those two Q-Jets are the secondary rods: BC's for the 201 and AX's for the 215. Probably not worth arguing about who's info is "better".
Thread Starter
7th Gear
Joined: Aug 2012
Posts: 7
Likes: 0
cross your fingers
Got the Paper from Lars THANKS!!! WoW! Rebuilt the carb and going to install it tomorrow. Noticed a ton of Carbon build up on the plate and on the Intake Manifold. I am going to remove the intake tomorrow and clean the carbon out. Anything I should be aware of before replacing the Intake and new gaskets? Also 1234 plugs were very carboned up and 5678 were not? Any ideas?
Thanks guys and Lar for all the help!
Thanks guys and Lar for all the help!
Burning Brakes
Joined: Dec 2010
Posts: 848
Likes: 60
From: CA
Noticed a ton of Carbon build up on the plate and on the Intake Manifold.
Anything I should be aware of before replacing the Intake and new gaskets?
Ed
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,112
From: Crossville TN
The OP lives in Canada. If he blocks the crossover passage, it'll take him some warm-up time to get the choke/carb warm and working. That decision should be his, based on how many cold-weather days he wants to operate the car.
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
The choke will still operate normally.
3rd Gear
Joined: Sep 2012
Posts: 3
Likes: 0
quadrajunk
I have a 1969 Corvette L36 427 390hp. The engine is a numbers matching to the vin of the car. I am new to the Corvette world so I need some help!
I live in Calgary Alberta Canada at about 3300 feet above see level. I took the car out and my first impression was it was starving for fuel. I changed the fuel filter at the carb and checked the in line fuel filter. The in line filter seemed fine as air passed through it freely. I changed the points over to Electronic Ignition. I went with the under the cap model to keep the OEM look. I changed the plugs and noticed 1through 4 plugs were burt way worse than 5 through 8? After these minor repairs were done I took the car out again and the problem was still there. Seems to idel fine but as soon as I kick it down it bogs and seems to choke itself. The four barrels are not opening up. Its a Quadrajet but I dont think its original factory? Should I just replace the carb and see if that fixes the problem or is there a better option?
Thanks!
PS LOVE the car! A real dream to drive and what a head turner!!!
Cheers!
I live in Calgary Alberta Canada at about 3300 feet above see level. I took the car out and my first impression was it was starving for fuel. I changed the fuel filter at the carb and checked the in line fuel filter. The in line filter seemed fine as air passed through it freely. I changed the points over to Electronic Ignition. I went with the under the cap model to keep the OEM look. I changed the plugs and noticed 1through 4 plugs were burt way worse than 5 through 8? After these minor repairs were done I took the car out again and the problem was still there. Seems to idel fine but as soon as I kick it down it bogs and seems to choke itself. The four barrels are not opening up. Its a Quadrajet but I dont think its original factory? Should I just replace the carb and see if that fixes the problem or is there a better option?
Thanks!
PS LOVE the car! A real dream to drive and what a head turner!!!
Cheers!
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
FYI - the reason they're called "quadrajunks" or "quadrabogs" stems from people who don't understand how the various systems work and muck them up in the process.