I will see if I can find the thread.
Gas drain back
- Thread starter Cornpatch MO
- Start date
FYI the gas doesn't drain back to the tank. It evaporates from the float bowl. A thick carb base gasket usually takes care of the problem. Guys that run a alumimum intake have less issues. Blocking off the heat riser passage helps as well. A electric pump or a priming pump takes care of it too. Some have installed a fuel filter with a return line to the tank that helps with the vapor lock when running. Still looking for the post with the part number of the electric prime pump.
Cornpatch MO
Well-Known Member
Thanks Mike, I found it. Summit has several different ones--I just need to choose which one .....MO...
niteshift92
Member
Fuel will run back towards the tank with a leaking fuel pump diaphragm or bad check valve due to the fuel inlet being above the level of the tank. Generally though, the engine will start on what is in the carb (or try to anyway), die, then restart when the fuel returns. Easiest way to make sure it isn't a pump issue, after the engine sits for a few hours, disconnect the fuel inlet to the carb and connect a two foot length of spare fuel hose dumping into a twenty ounce soda or water bottle. Unplug the coil so the engine doesn't start. Have someone turn the engine over as if trying to start it while you observe the bottle. Six to eight rotations of the engine should fill the bottle over half full (Half is fair, three quarters is better). If it doesnt or it takes time to prime itself, its the pump. If it's the pump, be sure to smell the crankcase oil. A leaking pump diaphram will leak fuel into the crankcase and contaminate the oil. Change it if it smells like gas.
My cars are higher in the rear so the gas can't drain back. LOL And I still have the evaporation problem.
niteshift92
Member
I have seen some carbs atop an aluminum plate that extends past the carb body by about an inch or more on all sides serving as a heat shield. I always found the thick(1/4 inch) pressboard/cardboard type gaskets worked well, similar to what you would find under a Quadrajet carb. Always use the phenolic spacers and not the aluminum.
Fuel will evaporate from the float bowl regardless but is aggravated by hot carb temps.
Mikeys73
Member
Same Problem on my 73 B-100 Van with Edelbrock 1405 carb. After pulling the van into the garage on a hot (80+ deg) day the fuel would boil and the garage smelled like I pored gas all over the floor. After installing a 1" Phenolic plastic spacer (Edelbrock 8711) the gas smell problem went away although if I don't start the Van for a few weeks I still have to crank it for a while to to get fuel to the carb. Because my application is a Van I also had to install a drop air cleaner pan and modify some linkage to get my clearance back for the engine cover to fit.
Just recently installed a 2nd fuel filter at the Carb (stock filter is under van), I sloped the feul line to prevent fuel from running back toward the stock pump so the filter remains full after shutting down, I am hoping this small amount of fuel will reduce the amount of cranking I need to do after the van sets for a few weeks. Will not be able to test this theory until this winter. If you look hard you can see the spacer in the photo...
Just recently installed a 2nd fuel filter at the Carb (stock filter is under van), I sloped the feul line to prevent fuel from running back toward the stock pump so the filter remains full after shutting down, I am hoping this small amount of fuel will reduce the amount of cranking I need to do after the van sets for a few weeks. Will not be able to test this theory until this winter. If you look hard you can see the spacer in the photo...
The see through filters are great but I recommend a metal filter. (especially on a van)
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