1996 Merc 200 efi rattle or knocking and seems to be ignition?

hbuilder43

Cadet
Joined
Aug 28, 2007
Messages
13
I have had my bass boat at a marine shop for going on 8 weeks now. The mechanic/owner can not find out the problem. On the water it may run 60 or 40. It may get out of the hole, or it may not. He has looked at the crankshaft and bearings, nothing bad, all good! Taken plugs out and looked at the top of pistons, all good. We were going to order a power head, but then he had second thoughts about it might be something in ignition or fuel that would still be there after a new power head. This mechanic has 40 years experience at this, but is puzzled!
When I took it in, I thought that it had a rattle. But after taking the engine cover off, it nearly sounds like a knock.
The boat was running fine when I took it to Falcon Lake in March. I know I got some bad higher octane gas at a small station there, and the next day it began to act up. I ran it 2 more days there, then 3 days at Lake Alan Henry. and the engine ran a little worse each day.
Can anyone offer a suggestion?
Thanks
 
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