The 2 stroke fuel pump
I have been a member for about a year, and have noticed that the same questions keep coming up. The most common problems are bad seals, dirty carburetor, ripped diaphragm in the fuel pump, and piston in backwards.
Since I just saw my old pump sitting there, I decided to take some pictures to show what is inside. Maybe someone will make this a sticky.
The fuel pump works on vacuum pulses from the engine, and must be airtight. The movement of the diaphragms move the fuel. The 2 check valves control where the fuel goes. A ripped upper diaphragm will result in weak or nonexistent fuel pressure. A ripped lower diaphragm will pull fuel into the crankcase, and cause a wet spark plug. You will think that you are getting fuel, and start looking for an ignition problem. Cleaning, or changing the plug will almost fix the problem for a few minutes driving you crazy. I believe that more than one unneeded HEI conversion has been performed because of a bad fuel pump.
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