3hp Briggs

bc realtor · Mar 9, 2010

I am reviveing an old 3hp briggs from about 1975. good compression, new points and condenser,BUT stalls after about 25 seconds. will not restart for some time. I have taken the carb screw and put it all the way in and then backed it off two turns. any advice on how to fix this or what the problem may be?:confused2:

RandyT · Mar 9, 2010

i would replace the fuel pump diaphragm

Stonehaller · Mar 9, 2010

If the carburetor has a float and gas tank above the carb, then check to make sure any strainer in the fuel line is clean and that the needle valve and float is not getting stuck. If fuel flow to the bowel is slow, then as the engine is running it sucks fuel from the bowel and it cannot be replaced fast enough so the engine runs of gas and stalls. Then the bowel slow fills up and the engine will start again.

If it is one with the gas tank attached below the carb then the above issue is not the problem. It could be crude in the tank blocking the fuel pickup or it may be an ignition problem. Immediately after the engine stalls, does it still have spark?

Travelover · Mar 9, 2010

Does sound like a fuel problem. I'd take the carb apart and blow out all the passages and as has been mentioned, make sure gas is flowing to the carb if it has a separate fuel tank.

mostly_gas · Mar 9, 2010

one of the 3hp Briggs had a problem with the tank flatness and required a thin nylon washer to pump gas up to the carb. If you want to skip the washer the machined portion of the gas tank needs to be flat within .002 inch.

BXpanded · Mar 10, 2010

If the tank is below the carb, there is a diaphram type fuel pump that pumps the gas up to a small bowl inside the top of the tank. (This bowl is built in inside the tank so you can't see it externally.) The fuel pickup tube goes down to the bottom of the tank and has a small screen on the end. Inside this non-removable screened end is a check valve that has a tendency to stick in the closed position preventing any fuel from being pumped up to the float bowl. You can't get the screen off and you can't readily get the pickup tube out of the carb... The check valve is obviously not intended to be a serviceable item. I've had this problem on 2 engines. I've managed to get both check valves working with carb cleaner and compressed air.
At least one of the engines would run fine as long as the gas tank was completely full. When the gas level dropped about 1/2 inch, the engine stopped. (The other might have run with a full tank as well but I hadn't blundered across the idea at the time.)

tommu56 · Mar 10, 2010

These engines use the crank case pulsation to pump the fuel to the cup to the tank for the pick up tube (like BXpanded said) if the crank case is not sealed bad gasket, oil cap off, or something similar no pulse no fuel or low fuel flow.

tom