by KE4AVB » Tue Dec 01, 2015 10:44 pm
In order for the engine to run with trigger not pull the unloader must be un-load pressure generated by the pump. A bad unloader would overload the engine when the trigger is not pulled as it would not unload the pump. I would think it is more likely a carburetor problem as these engines run off the high idle carburetor circuits until loaded down by the pressure pump then the carburetor would switch over to the main jet/nozzle for the additional needed fuel mix as the governor demands more throttle.
I have had several pumps here where the unloader were bad or stuck closed and the only way to start the engine was for pressure ward trigger be help open (pulled). Now a bad unloader can also cause a lack of pressure build-up if its regulator spring is shattered. This the same as if one of the check valves, pressure seals, or o-rings were bad.
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