C-1 Gas Percolation

[Nicholas L.]

This past Sunday I observed what I think is gas percolation in my 1960 270HP Corvette. After driving about 30min.,I stopped my car and turned off the engine because it seemed to be idling rough. I removed the air cleaner and I could see gas coming out of one of the nozzles on the rear carb. I remember reading post about one year ago about percolation and checked the archives. There were several suggestions,i.e. fuel line insulation,octane booster,checking carb. vent. Has anyone fixed this problem and by what means? Thanks in advance for any
advice.

[Ed Jennings]

Re: C-1 Gas Percolation

If you have a heat riser, be sure it's operating. Many folks disable them or remove them completly for just this reason.

[John H.]

Re: C-1 Gas Percolation

Nick -

This is frequently one of the joys of the newer re-formulated and/or oxygenated gasolines. Several things help here - one is double gaskets under the WCFB's to help insulate them from manifold heat, another is to change the float settings from the original 1/8" (primary) and 1/4" (secondary) to 1/4" and 5/16" to allow space in the float bowls for expansion.

[Clem Z.]

Re: C-1 Gas Percolation

try blocking the heat riser crossover passage under the intake. a second advantage is more HP

[Mark Ring]

Re: C-1 Gas Percolation

Last week I blocked mine on one side and put the restrictor insert on the choke coil side (just in case I ever went to a non-electric choke carb setup). I also made some other changes to the initial timing in the distributor and some fuel changes to get rid of the excessive octane/lead additives. I know this is not the "scientific method" but I do not have unlimited time lately to do these things indepenantly of each other then test and evaluate each change one at a time (is that a "Yogi-isim"?). The results were sucessful in curing a hot soak carb issue but the minor downside is what was warned that I now have a minute or 2 longer warmup requirement for the carb. Nothing I can't handle and worth the sacrifice without question.

-Mark.

[Clem Z.]

warm up time

with a aluminum intake should be no problem but cast iron manifolds take forever to warm up but they do not transfer the heat to the carb like the aluminum manifolds so a heat insulator spacer under the carb may work on a cast iron manifold instead of blocking the crossover.