Question for you brainiacs. My 78 will run all day sitting in the garage or outside and when I shut it down, I do not get any fuel leaking into the intake or gas smell. I take it out for a short romp, 30 miles, and park it in the garage, I can remove air cleaner cover and see wisps of gas fumes comming from the primaries and within an hour, the garage smells like you dumped a can of gas on the floor.

Was wondering if the EGR could be causing the problem. It was removed by the previous owner and it looks like the stem was pulled up and bent over. Engine timming and carb adjustments have been checked and vacumm is 17 at 900 rpms with the auto trans in park. Good throttle response, I think, as performance is what I would expect from a stock engine. Been under it and chased the gas lines, both running and off, no fuel leaks.

Any ideas before I start tearing things apart ??

fuel percolation..causing flooding after hot shutdown..is there an insulator type gasket under carb?

Yes, looks to be ~ 1/4 inch.

Fuel appears to be leaking from below butterfly throttle plate.

No more driving, winter has set in and we have 5 inches of snow and another 4 on the way today.

then its likely a float malfunction or a crack in the bowl area that only leaks after its hot and expanded..overtightening causes cracks in q-jets..sorry about snow..its 81 degrees here, never put mine away for winter

it's *72 here Love the south :woowoo:

Good luck at least you'll be ready for spring!!!

fuel percolation..causing flooding after hot shutdown..is there an insulator type gasket under carb?


About 2-3 minutes after I shut my 454" engine off I can hear the gasoline boiling in the carburetor.

yeah, we both know its a common thing, the thick insulator gasket helps, but 454s hold a lot of heat.,that big iron manifold stays hot for a while..hows that new trans working now Toobroke?

I was afraid of the carb being cracked, but will see if I can get a thicker insulator gasket and give the carb a good inspection then check the float level.

yeah, we both know its a common thing, the thick insulator gasket helps, but 454s hold a lot of heat.,that big iron manifold stays hot for a while..hows that new trans working now Toobroke?


I was in the process of getting my shift points where I wanted them then I parked it and started in on my new paint job. I'll have it painted within the next week then I can start driving it again. Those 700R4's are sure slick. It ended up costing me about $1600 for the TH400/700R4 conversion but it'll pay for itself in no time. With it's 30% overdrive I'll instantly see 30% better fuel mileage and less wear-and-tear on my new (rebuilt) 454" engine.

should look as good as it runs now.Blue again?that 700r4 is slick,when built right, its perfect for our cars

should look as good as it runs now.Blue again?that 700r4 is slick,when built right, its perfect for our cars


Mulsanne Blue is what it's called. Real bright "electric" blue. I'm planning on shooting the first color coats today.

It was boiling the fuel. Got a new manifold to carb gasket and it is definetely thicker than what was on there.

Had to move some stuff around in the garage stall in the barn. Moved the vette out, before I installed the new carb/manifold gasket, into the cold 18 degree air and set the idle up to 2500 and ran it for about 45 minutes. Drove it back in the garage stall in the barn and shut it down. No fuel boiling or smell. I think that replacing the carb/manifold gasket will fix the boiling problem when it warms up next summer.

toobroke - - wher did you get the 700r4 conversion from ??

Toobroke - - Where did you get the 700R4 conversion from ??




I didn't buy any "conversion" kit. When I ordered the transmission parts from P.A.T.C. I also ordered a new tail housing that had a mount on it. That really helped because I only had to slot my crossmember 3/4". I had Driveline Service in Fresno shorten my driveshaft 1-1/2" and I fabricated the rest of the parts. The oil pan on TH700R4's is offset to the right side about 2" so the right side is up against the transmission tunnel. And as the TH700R4's oil pan is a lot wider than a TH400's pan I have to remove the left side exhaust pipe to pull the pan off. When I did the swap I also put an 1/8" NPT allen head drain plug in my torque converter and oil pan.

It was boiling the fuel. Got a new manifold to carb gasket and it is definetely thicker than what was on there.

Had to move some stuff around in the garage stall in the barn. Moved the vette out, before I installed the new carb/manifold gasket, into the cold 18 degree air and set the idle up to 2500 and ran it for about 45 minutes. Drove it back in the garage stall in the barn and shut it down. No fuel boiling or smell. I think that replacing the carb/manifold gasket will fix the boiling problem when it warms up next summer.
glad to hear that solved the percolation problem..as for the 700r4, if you are considering doing the swap, Monster Transmission has a conversion package.. http://racetransmissions.com/store/index.php/cPath/167..

A Q-Jet has two lead plugs in the bottom of the float bowl that are possible points for a leak. And they will drain the gas into the intake and appear to be under the throttle plates.

When I shut her down, I popped the hood and air cleaner, no hissing or bubbling sound. Waited a couple of minutes and stuck my nose in the carb, only a faint smell of gas. Cracked the throttle and looked in with a flashlight, no pool of gas, just barily damp from cracking the throttle and putting the gas into the intake, could smell the gas. Let it set for 2 days, and it fired right up with just the 'ye old 1 gas peddle pump'.

All of this might end up be acidemic if I pop for a new higher HP engine before the spring gets here.

it sounds like that was the problem..its a very common thing..the phenolic gaskets work pretty well to stop heat transfer..and you can never have too much horsepower! too much is just right!

A Q-Jet has two lead plugs in the bottom of the float bowl that are possible points for a leak. And they will drain the gas into the intake and appear to be under the throttle plates.

These plugs are called " fuel well plugs" They never leak when cool. But when hot you can tell when a fuel droplet leaves the well plug as it causes a stumble in the idle every time. There are repair kits out there to address this problem, but I have only had about a 50% success rate with them.

I got a replacement, unrebuilt original carb, YA! Same number as the original with a build date 26 days before the one that currently is on my vette!! I was surprized to find it !! A local junkyard might have other treasures as the owner says there are several older wrecked vettes back there amongst the trees, once the snow melts that is.