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In Reply to: 240 engine backfire posted by Rob on Tuesday, March 11, 2008:
Dana- good question. I have checked the flywheel key and it is ok, these keys are heavier than a tecumseh or briggs key.they dont seem to break as easy.
Henry-good point, unfortunately the timing is set by the crank to flywheel position and is not adjustable. the timing should be correct if danas idea has not occured. the spark will fire on exhaust stroke due to the 2 to 1 ratio of the flywheel to cam. this is why I believe the backfire is occuring during this stroke. the timing isnt 180 off, its only 1-2 degrees off and the intake valve is opening too early, igniting the mix in the intake during a normal 2nd fire of the plug.
I cant find the problem causing this(cam/ crank timing marks on gears are ok). Possible twisted crank?