My engine developed this problem last week. After being out all day it suddenly wouldn't rev up at all. In nuetral it would only rev up to 2200rpm. when put into gear it got rough and would quit immediatly. Smoke was slightly more than usual but by no means excessive. This occured once before but only last for a couple minutes and I figure the fuel may have picked up a contaminant. this time however it lingered and resulted in being towed in. Engine requires choke to start but immediatly choke must be turned off and seems to idle fine. New plugs and entire fuel delivery( pick ups, line, filters, etc). Thank you