Join Date: May 2007
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It could be a fouled prop or a rope around the shaft, but often these conditions will give you heavy, if not black exhaust smoke. The everything is good underwater is in good shape I would say the engine is starving of fuel (abnormal exhaust smoke is not usually a symptom here). Possible causes include clogged fuel filters, a failing lift pump, or an air leak.
Your primary filter should be a 30 micron filter, and the secondary should be the OEM filter. They should be changed at the same time.