weak fuel pump

[mhooper]

I know that a impulse fuel pump works off the positive and negative pressures in an engine, what causes the pressure to weaken enough that a fuel pump won't work? Compression good, valves refaced and new head gaskets on a Tecumseh TVT691

 

[mechanic mark]

http://www.barrettsmallengine.com/tecumseh/manuals.html

your engine repair manual