there could be one more problem if what you are calling jams up is actualy snatching back it could be the flywheel key
bubbafw
June 2010
Gary,
First, check up under the mower. Is there any debris interfering with the blade? Next, remove the spark plug or plugs, then try pulling on the starter cord. There could petrol in the combustion chamber. Thirdly, remove the cover that houses the pull rope. Check to see if the rope is tangled within the spool. If all of these prove to not be the problem, then there is a serious engine issue(seized bearing, damaged crankshaft, damaged camshaft, valves, etc).
Good Luck!
Gunny63
June 2010
Automatic Answer
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