1965 L79 carb leaking after engine is turned off

[James W.]

The carb on my 1965, L79 equippped Corvette that was recently rebuilt by one the well known rebuilders is experiencing some gasoline leaking out onto the intake manifold (both sides) after the engine is turned off. Not right away but maybe 30 to 45 minutes after the engine has been turned off. I have adjusted the floats per the shop manual, even lowered them to see if this made any difference, which it did some but did not completely eliminate the problem. I run the 92 octane BP premium gasoline in the car.

Is there another adjustment that needs to be made or is the some issues with surfaces not being flat or true causing the leaks or possibly things not being tightened enough?

Thanks,

James West
Omaha, NE.

[John H.]

Re: 1965 L79 carb leaking after engine is turned o

Could be fuel percolating during hot-soak out of the boosters, dripping on the throttle shaft, and weeping out of the end(s) of the throttle shaft onto the manifold.

[James W.]

Re: 1965 L79 carb leaking after engine is turned o

John,

Thanks for the reply. Is there a "fix" for this? Is it possible that I do not have an insulating gasket installed between the carb and intake manifold? Would his cause this condition?

Thanks,

James West

[Jeff S.]

Re: 1965 L79 carb leaking after engine is turned o

James

I doubt if an insulation piece would help; the heat soaking (& thus gas expansion) is typically via convection heating from the primary float bowl hanging over the intake manifold runner, not by conduction through the carb base plate. I was able to mitigate this on a 300HP base engine by use of an aluminum heat shield with appropriate bends/angles to achieve a dead air space. It may also work on L79, although your aluminum intake itself should sink off considerably more heat than a cast iron unit.

[Paul L.]

Re: 1965 L79 carb leaking after engine is turned o

James,
Had the same problems four years ago. Drove me crazy. I know this is heresy on this Board, but I just put on an Edelbrock #1406 and have had four years of trouble-free cruising. The Holley is in the basement awaiting the next owner of my 1967. I wish he/she luck with it. Just a fire-trap. The stink, the smell, the leaks, etc.

[Dave K.]

Re: 1965 L79 carb leaking after engine is turned o

I would also block open your heat riser valve for the hotter weather driving. I did on my 66 base engine car and it helped. I also plugged the under carb crossover passage on my cast iron manifold. Do not think that the aluminum manifolds have this passage

Dave K.

[Joe R.]

Re: 1965 L79 carb leaking after engine is turned o

I had this same problem on my 67 300 HP when I first got the car. The carb was a correct 3810 but it was a service replacement. When I replaced the carb with a freshly rebuilt, correct dated 3810, the gas leakage problem disappeared.

So, I think your problem is with the carb rebuild. If you park the car hot, take off the air cleaner, and watch for about 10 minutes, you should be able to see where the gas is coming out. I suspect that John Hinckley is correct that it is coming out around the throttle shaft, either the primary or secondary.

If you see it coming out around the throttle shaft, look down the throat of the carb to see if you can see gas dripping on the throttle valves. The source of the gas should give you some info that you can provide to your carb rebuilder in hopes that he can fix the problem.

[Gerard F.]

Has anybody ever checked

the pressure in the gas tank after a long hot run. I know that the C2's have vented gas tanks, but they build up to a certain pressure before they relieve by the design of the stock cap. I notice on my 67 that after a long hot run, stopping for gas, that when you remove the gas cap you get a whoosh out of pressure relief from the tank. I think it has to do with the heat from the mufflers.

So maybe that drip drip drip after you shut it off is just pressure relief from the gas tank. Next time it happens try pulling the gas cap and see if it stops.

Just a thought, my percolation theory, maybe I'm crazy. Any comments

Jerry Fuccillo
#42179

[Phil P.]

Re: Has anybody ever checked

jerry,i had the same problem with a 68 bb camaro with the transverse muffler in front the the gas tank---i vented the filler neck, much like the over flow hose on a vet,down to the lower valance and it cured the carb leak issue---phil

[Clem Z.]

Re: Has anybody ever checked

on the corvettes we just drilled a 1/8" hole in the gas cap.

[James W.]

Re: Has anybody ever checked

Jerry,

Good point, I will give this a try. Last night I went out and drove the car to the car wash. When I came back a wiped the car off I noticed that it did not seap near the amount of gas as it did on Sunday. It was much cooler high 50's, actually cold compared to the upper 70 degree temps on Saturday and Sunday when I really noticed it. I'll will try loosening the cap and see what happens.

Thanks,

James West

[Michael M.]

Re: Has anybody ever checked

Here is something I just ran into with my L79 after I installed the engine. The carb had run fine and never leaked. As I was sorting things out I had it leak several times. Finally I pulled the accelerator pump to replace the gasket and the pattern on the old gasket looked irregular. I checked the gasket surface on both the carb bowl and the pump body and both were not flat at all. Careful use of a fine file on both surfaces, a good clean up to get rid of the fines and a new gasket and the leak is gone - for good I hope.

Mike Marion