So I recently purchased a 2005 trail boss 330 fired just didn’t run, been sitting seemed like carburetor issue… I took the carb off and ran it through my ultrasonic cleaner to learn the fuel pump was bad, replaced fuel pump and got it running but only with lots of throttle or fiddling with choke, checked the spark plug to see it was all black and nasty with carbon build up. New plug and it started right up and ran the best it has since I got it, but still won’t idle… after inspecting the new plug after only running on throttle for about a minute or 2 it was all black and built up with carbon again. It also has doesn’t sound the happiest when it’s running… I checked the valve lash and it seems good… what could it be? I linked a video of it running…. Please help. YouTube
Myself; I would remove the spark plug and put a dial indicator on the piston - put a degree wheel on the crankshaft and rock the engine back and forth watching the dial indicator to detect movement of the crank with a delay of movement of the piston which will indicate play between the crank and rod or piston pin and piston. If no play is detected in the piston movement, then further investigation is required to determine if it's a loose flywheel, broken piston or ??????????
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