I have a briggs and Stratton 5 HP engine on an old JC Penny horizontal shaft Roto tiller. I replaced the gaskets in the Carburetor and it was running fine for a few hours. The next day,went to use it, and now when I idle down after starting to a medium engine speed, gas shoots out from the Gas tank cap vent. an actual stream. I assume it is building up pressure in the tank for some reason. I suspect that maybe there is a leaking exhaust valve blowing pressure back into the Carb. Any suggestions?
It sounds to me like your gas cap vent is plugged or restricted. If it is restricted, then pressure will build up in the tank until it overcomes the restriction. Remove the cap and ensure the vent is clear.
Good luck.
The gas cap vent is fine, I have check it, it is not plug. This is the type of carb where there is no float nor a needle valve. It uses a spring, diaphragm and check valve in the form of the gasket. Engine suction moves the diaphragm as a pump to suck gas up the tube and to the needle valve and throat of the carb. This is common on the older B&S engines.
I understand what you are saying, but since you never posted the numbers for the engine, I assumed that you had a gravity feed carb. The only way that I known of, that a pulsa jet carb with shoot fuel out of the gas cap while the engine is running, is because the tank is full to the top and being on a tiller the engine is bouncing around. There is no way that a leaking valve can cause this problem.
Thanks a bunch for the tip. You could be right, as I had filled the tank that next day, and it was almost topped off. You know, I would have never thought of that. I'll drain some gas from the tank:smile: and try it again.
Thank again for the advise.
