Fuel dripping
Thread Starter
Instructor
Joined: Jan 2007
Posts: 233
Likes: 41
From: Simpsonville SC
Fuel dripping
I’m having problems getting my 78 L-82 to idle at the correct RPM. Sometimes I adjust the idle screw and get it at the correct RPM. Then take it for a drive and notice the idle RPM has jumped up. I started looking around and noticed fuel dripping off the Quadrajet ventures. This is not supposed to happen at idle correct? Sometimes the dripping stops and the engine will idle at a low RPM. What would cause this? Any help would be appreciated.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,392
From: At my Bar drinking and wrenching in Lafayette Colorado
At idle, there should not be any fuel discharged from the main discharge nozzles on any carb (from the "venturi"). Causes for fuel dripping from the venturi are as follows:
1. Incorrect float level. If float level is too high, fuel will drip from the nozzles.
2. High fuel pressure. Excessive fuel pressure can cause #1.
3. Excessive throttle opening. If the idle speed screw is cranked in too far, the carb will idle on the main discharge circuit instead of on the idle circuit. This can be cause by the following:
a. Insufficient initial timing. Check timing, timing advance, and fuinction of the vacuum advance control unit.
b. Carb setup problem. If the carb is a commercially rebuilt carb (see my postin on this), there are several internal issues that will prevent the carb from idling on the idle circuit, including modified power piston (cut lower stop), plugged idle air bleed holes (intentially installed lead plugs), plugged idle fuel transfer tubes, low float level, lean setting of the APT, lean jetting, warped airhorn eliminating idle fuel transfer, and incorrectly set idle mixture screws.
Good luck with the tuning!
1. Incorrect float level. If float level is too high, fuel will drip from the nozzles.
2. High fuel pressure. Excessive fuel pressure can cause #1.
3. Excessive throttle opening. If the idle speed screw is cranked in too far, the carb will idle on the main discharge circuit instead of on the idle circuit. This can be cause by the following:
a. Insufficient initial timing. Check timing, timing advance, and fuinction of the vacuum advance control unit.
b. Carb setup problem. If the carb is a commercially rebuilt carb (see my postin on this), there are several internal issues that will prevent the carb from idling on the idle circuit, including modified power piston (cut lower stop), plugged idle air bleed holes (intentially installed lead plugs), plugged idle fuel transfer tubes, low float level, lean setting of the APT, lean jetting, warped airhorn eliminating idle fuel transfer, and incorrectly set idle mixture screws.
Good luck with the tuning!
Thread Starter
Instructor
Joined: Jan 2007
Posts: 233
Likes: 41
From: Simpsonville SC
I’m working with my carb rebuilder on repairing my fuel drip. When I got the car it had a 17059216 but it’s supposed to have a 17058211 correct? It’s a 78 L-82 manual. Here’s the info from Lars carb running doc. Does the jet and rod sizing look correct?
Carb # Application Jet Rod Spring
17058211 CHEV 78 FED VETTE H.P. 77 53 17052057
17059216 Chevy 79 305-350 Camaro 72 40 17036019
Carb # Application Jet Rod Spring
17058211 CHEV 78 FED VETTE H.P. 77 53 17052057
17059216 Chevy 79 305-350 Camaro 72 40 17036019
Race Director
Joined: Jul 2002
Posts: 13,858
Likes: 0
From: A 12/8 man in a 4/4 world
also check all the vacuum fittings.
I had similar symptons. I finally noticed a crack vacuum cap (primary) that was playing havoc with my idle.
replace all caps and lines.....
no problem
I had similar symptons. I finally noticed a crack vacuum cap (primary) that was playing havoc with my idle.
replace all caps and lines.....
no problem
Thread Starter
Instructor
Joined: Jan 2007
Posts: 233
Likes: 41
From: Simpsonville SC
Well, got my carb back and the 1st thing I noticed was now my primary throttle plates each have a small hole drilled in them. Why would the rebuilder have done this? I plan to call them tomorrow. I still have fuel dripping from main discharge nozzles. I haven't checked my fuel pressure yet, guess thats next.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
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
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Make sure they havent blocked your fuel return line.
Thread Starter
Instructor
Joined: Jan 2007
Posts: 233
Likes: 41
From: Simpsonville SC
I continue to have problems carburetor and commercial rebuilder 
. I Finally said the heck with it and opened the carb up to check it out. The float was a bit high. But I checked the air horn for warpage and this is what I found. http://picasaweb.google.com/Walllparty/Carb It looks like the edges are lower than the center. Am I hosed?
. I Finally said the heck with it and opened the carb up to check it out. The float was a bit high. But I checked the air horn for warpage and this is what I found. http://picasaweb.google.com/Walllparty/Carb It looks like the edges are lower than the center. Am I hosed?
Thread Starter
Instructor
Joined: Jan 2007
Posts: 233
Likes: 41
From: Simpsonville SC
Update, well I did find the plugged idle air bleed holes just like Lars said.
I took some pics> http://picasaweb.google.com/Walllparty/Carb_plug
I guess that why the rebuilder drilled holes in my primary throttle plate. Now that I have removed the plugs I need to replace the throttle plates correct? I also found the float to be a little high and the power piston needing some adjusting as described in Lars Qjet tuning doc. Buttoned everything back up and retested on the car. Bummer, still have fuel dripping out my primary discharge ports. Oh, one other thing to mention. If I look down into the area around the secondary rods when the car is running, I can see fuel. Is that normal? The battle continues......
I took some pics> http://picasaweb.google.com/Walllparty/Carb_plug
I guess that why the rebuilder drilled holes in my primary throttle plate. Now that I have removed the plugs I need to replace the throttle plates correct? I also found the float to be a little high and the power piston needing some adjusting as described in Lars Qjet tuning doc. Buttoned everything back up and retested on the car. Bummer, still have fuel dripping out my primary discharge ports. Oh, one other thing to mention. If I look down into the area around the secondary rods when the car is running, I can see fuel. Is that normal? The battle continues......
Last edited by bytor; Sep 9, 2007 at 11:44 AM.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,392
From: At my Bar drinking and wrenching in Lafayette Colorado
Send me the carb and let me test it.
Melting Slicks
Joined: Mar 2006
Posts: 3,342
Likes: 7
From: Connecticut
Thread Starter
Instructor
Joined: Jan 2007
Posts: 233
Likes: 41
From: Simpsonville SC
Thanks Onit, I will keep that in mind. Actually, I was successful in sending the carb back to the rebuilder and getting my money back. I have picked up a few carbs on ebay and one of them is a 17059211. This is the 79 version of what I need for my 78 L-82. I’m rebuilding it now. One thing I noticed is the 211 is an 800cfm carb. I assume this is a key difference in the requirement for an L-82 application. The 78-79 211 series are rare it would seem. I currently have a 17058204 that’s on the car. I enlarged the idle air bypass and mixture screw holes with positive results. The drip is almost gone and the car runs much better now. Lars, what’s your thought in the 750 vs. 800 cfm carbs and their applications? With modifications, can you run a 750 on a car that originally had a 800?
Thread Starter
Instructor
Joined: Jan 2007
Posts: 233
Likes: 41
From: Simpsonville SC
I'm one step closer to carburetor nirvana! I have my 17059211 on the car now and things are much better. Idle quality has improved significantly, no more off idle issues, off the line performance is much better and I can 'feel the secondaries kick in now. The only nagging problem is my fuel bowl level. When I rebuilt the carb, I installed a NAPA 2-442. I have the problem of the air horn gasket getting wet when looking down around the secondary metering rods. I wasn't able to finish my diagnostics last night but I did install another float I had on hand. It was bigger that the 2-442. This seemed to help but I think I still have an issue. I do have an aftermarket fuel pump (Autozone) special on the car now. I have checked the pressure and at idle, it is 6psi. Is this OK? Can I rule out fuel pressure as the culprit.
Thread Starter
Instructor
Joined: Jan 2007
Posts: 233
Likes: 41
From: Simpsonville SC
Well, partially answered my own question after more troubleshooting and beer. It would seem the smaller float was not the problem. It was the float hinge pin that was the culprit. It was bent and did not contact the air horn so the it would cause the needle not to seat correctly. I discovered screwing a screw with a few washers into the power piston adjustment hole would retain a normal float hinge correctly. But not the one in question because it was bent and would flop allover the place. Still need input on the fuel pump pressure question though..