I need help with a Quadrajet
Thread Starter
Racer
Joined: Mar 2012
Posts: 476
Likes: 37
From: Lynnwood WA
I need help with a Quadrajet
While doing a compression test on my 79 today I noticed that someone had hacked off part of my front vent tube. Then when locking my throttle linkage open I noticed that gas was flowing over the top and down the front of the carb. In fact it does it every time I operate the linkage! This is with the car not running of course, at least I sure hope it's only when the car is not running. Any ideas on why it would do this?
Thread Starter
Racer
Joined: Mar 2012
Posts: 476
Likes: 37
From: Lynnwood WA
Drifting
Joined: Mar 2011
Posts: 1,886
Likes: 9
Carb is flooding.
Here in NJ, where they add ethanol (good for the ADM stockholders, at least) and who knows what else to the gasoline, the plastic floats don't last for long. I had one last only five months before it got heavy and sank. I changed over to a brass float, thinking it would be impervious to the fuel additives. I know Lars doesn't like the brass floats, but it's better than changing them constantly.
Here in NJ, where they add ethanol (good for the ADM stockholders, at least) and who knows what else to the gasoline, the plastic floats don't last for long. I had one last only five months before it got heavy and sank. I changed over to a brass float, thinking it would be impervious to the fuel additives. I know Lars doesn't like the brass floats, but it's better than changing them constantly.
Tech Contributor
Joined: Aug 1999
Posts: 14,376
Likes: 6,375
From: At my Bar drinking and wrenching in Lafayette Colorado
Based on the appearance of the carb in the photo, you have a commercially rebuilt carb. It is likely to have at least a dozen internal problems and issues, several of which can contribute to the flooding issue: I doubt you only have one problem in there... You can drop me a request for my "Commercially Rebuilt Q-Jet Issues" paper if you'd lke to get an oversight of the possible problems.
Lars
V8FastCars@msn.com
Lars
V8FastCars@msn.com
Thread Starter
Racer
Joined: Mar 2012
Posts: 476
Likes: 37
From: Lynnwood WA
Based on the appearance of the carb in the photo, you have a commercially rebuilt carb. It is likely to have at least a dozen internal problems and issues, several of which can contribute to the flooding issue: I doubt you only have one problem in there... You can drop me a request for my "Commercially Rebuilt Q-Jet Issues" paper if you'd lke to get an oversight of the possible problems.
Lars
V8FastCars@msn.com
Lars
V8FastCars@msn.com
Zorro.
Burning Brakes
Joined: May 2009
Posts: 850
Likes: 36
From: Providence RI
While doing a compression test on my 79 today I noticed that someone had hacked off part of my front vent tube. Then when locking my throttle linkage open I noticed that gas was flowing over the top and down the front of the carb. In fact it does it every time I operate the linkage! This is with the car not running of course, at least I sure hope it's only when the car is not running. Any ideas on why it would do this?
If your car is not running, fuel is not being pumped into the carburetor, so there should be no way it would be bubbling out the top of the vent-tube.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
Uhhhh....the fuel pump will continue to shoot fuel to the carb as long as the needle valve is "open". So, if it doesn't seal well, and you rev it up [to make the fuel pump work harder], it belches the excess out the vent.
Burning Brakes
Joined: May 2009
Posts: 850
Likes: 36
From: Providence RI
Please read his original post:
In fact it does it every time I operate the linkage! This is with the car not running of course, at least I sure hope it's only when the car is not running. Any ideas on why it would do this?
Thread Starter
Racer
Joined: Mar 2012
Posts: 476
Likes: 37
From: Lynnwood WA
Are you sure the fuel is overflowing the top of the vent-tube, and not merely being shot out the accelerator-pump nozzes? (as it should)
If your car is not running, fuel is not being pumped into the carburetor, so there should be no way it would be bubbling out the top of the vent-tube.
If your car is not running, fuel is not being pumped into the carburetor, so there should be no way it would be bubbling out the top of the vent-tube.
The vent tube is the only place on the front of the carb, I'm sure it is not leaking from. The fuel leaks when I operate the linkage. That would mean it would have all the gas that is in the float bowl plus when the float drops it would get a little more from any under pressure between the pump and carb if any. When I checked out the plugs when doing a compression test they looked black and wet. I had thought oil, but when I looked this morning they were dry and black. must have been unburned gas. At this point I think I will just get it off the car, before it burns my house down!
Zorro.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
OK, OK....I read too quickly to catch what is written, sometimes. :o
So, if fuel isn't being pumped to the carb, and the only 'action' is exercising the linkage, then, the accelerator pump must be sending fuel where it doesn't belong. The only 'exit path' from the accel pump chamber should be the fuel discharge openings in the primary venturi. But, there must be another path that pressurized fuel is taking. Removal and disassembly would seem to be the only course of action.
So, if fuel isn't being pumped to the carb, and the only 'action' is exercising the linkage, then, the accelerator pump must be sending fuel where it doesn't belong. The only 'exit path' from the accel pump chamber should be the fuel discharge openings in the primary venturi. But, there must be another path that pressurized fuel is taking. Removal and disassembly would seem to be the only course of action.
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
I'd be willing to help people go through stock carb rebuilds if they're in my area.
