The Stovebolt Site Forums The Shop Area Engine Shop '53 235 suddenly statrted running way too rich

I thought my suddenly over-rich running 235 was due to another ethanol inflicted accelerator pump diaphragm in my YF2100.
So I proceeded to remove the gas line from the carburetor, when a seemingly never ending flow of gas gushed out of the gas line. I quickly tightened up the gas line and took off the gas cap and a huge rush of air spewed out. I am assuming that the non-vented gas cap allowed pressure to build up, forcing gas to be pushed past the rubber tipped float needle, causing excess gas to go over the top of the bowl and into the intake. I drilled a 1/8" hole in the cap from the bottom and solved the problem.

It's amazing how so many things can be fixed by proper drafting.

I've been there and done that too!

Why are these gas caps sold as 'vented' caps? It seems like a number of us have experienced this situation with reproduction gas caps.

Some caps are marketed as "pressure/vacuum" and they vent only when the internal pressure in the tank goes above a certain level, or drops to a preset vacuum. Those don't work well in place of a cap with a simple vent hole. You can thank the tree huggers and their obsession with hydrocarbon vapors for that kind of nonsense!
Jerry

I suppose this the same reasoning behind the modern gas cans that have no vent/ inadequate vent. My 5 gal can takes about 6 hrs to empty. Every time I use it, I say I'm going to drill a hole. But then I hop on the mower and onto the next item and forget.

My 235 runs very rich in '50 car. Plugs carbon up rapidly. Installed the second rebuilt Rochester. All new plugs, points, condenser, Carter EL158 12 to 6 volt resister type coil. Spark jumps 1/2" with plug wire separated from plug. Drilled vent holes in gas cap. Any suggestions?

Check to see if you've got a vacuum passage covered up by the carburetor base gasket. If the power valve doesn't get vacuum, the piston stays down and the power system goes full rich and stays that way. Lots of gas bypasses the main jet and you have the equivalent of running full throttle/low manifold vacuum all the time.
Jerry

Thank you Jerry. Gasket was blocking vacuum passage to carburetor. Cut out gasket accordingly and runs much better. Plugs are staying cleaner so far. Vacuum gage reads low at 17-18". Not sure what that is telling me at this point.

Richen up the idle mixture by turning the needle valve CCW slightly and also raise the idle speed a little. A couple of degrees more timing advance might help.
Jerry