[C2] Quadrajet Problems
Thread Starter
Navigator
Joined: Mar 2018
Posts: 9
Likes: 1
From: Washington Illinois
Quadrajet Problems
I have a 1967 corvette convertible with a different engine that I believe is a 1969 350/300. The carburetor is a Rochester Quadrajet 4MV. I have some symptoms of a float level may be too high; fuel appears to seep out of the accelerator pump shaft hole, poor hot start, and poor fuel economy. In addition, cold start sputters, and requires revving the engine for a couple minutes to keep it running. After a couple minutes of this, it runs nicely, until you shut it off and then you may deal with the hot start issue.
When the engine is cold, the choke does not fully close, and when its hot, the choke is not fully open. It seemed it just needed a little extra push, so I bought a new choke thermostat coil that was supposedly right, and it didn't fit.
The engine based on the casting number (393286), and engine code (V1205HZ), I believe I have a 1969, 350 ci/300hp engine. The intake manifold casting number 3927184 GM2 (350, mold #2) with a date code of L2_0 (December 2nd, 1970). The Rochester 4MV Quadrajet is coded 7029223.
So before I just start throwing parts at the car, I am hoping you would have some insight as to my course of action.
Thank you in advance for your time and consideration
When the engine is cold, the choke does not fully close, and when its hot, the choke is not fully open. It seemed it just needed a little extra push, so I bought a new choke thermostat coil that was supposedly right, and it didn't fit.
The engine based on the casting number (393286), and engine code (V1205HZ), I believe I have a 1969, 350 ci/300hp engine. The intake manifold casting number 3927184 GM2 (350, mold #2) with a date code of L2_0 (December 2nd, 1970). The Rochester 4MV Quadrajet is coded 7029223.
So before I just start throwing parts at the car, I am hoping you would have some insight as to my course of action.
Thank you in advance for your time and consideration
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
Check your fuel pressure. Most replacement fuel pumps for Holleys on our C2s often test at 7 or 8 psi. The Q-Jet, which works best with 5 psi, can become flooded at the higher pressures especially after shutoff since there is no return line to the fuel tank like was used with C3s.
Le Mans Master
Joined: Nov 2015
Posts: 7,423
Likes: 2,597
From: Really Central IL Illinois
Sounds like the plastic float may have absorbed too much fuel. This was a problem back in the 70s and 80s. I replaced a lot of them. The difference in a fantastic Quadrajet and a Quadrajunk is the guy doing the rebuilding. I never mastered the tuning on them, but have known a few that made them perform on Chrysler products.
Thread Starter
Navigator
Joined: Mar 2018
Posts: 9
Likes: 1
From: Washington Illinois
Sounds like the plastic float may have absorbed too much fuel. This was a problem back in the 70s and 80s. I replaced a lot of them. The difference in a fantastic Quadrajet and a Quadrajunk is the guy doing the rebuilding. I never mastered the tuning on them, but have known a few that made them perform on Chrysler products.
Pro
Joined: Mar 2020
Posts: 500
Likes: 27
The air force sent me to a GM Rochester qjet tuning class in Memphis around 1978. Wonder if I remember any of that stuff.
Le Mans Master
Joined: Apr 2013
Posts: 5,000
Likes: 1,056
From: Arlington TX
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I’ve got the same engine, a 69 350 with a Quadrajet. I had a lot of trouble with it until I finally ignored the textbook float setting and set it at .3”, per Lars recommendation. Now it runs great, wished I had done that a long time ago. Verify your float is okay, then set it at .3” and try it.
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