25 merc rattle , knock

Joined
Apr 20, 2004
Messages
23
It has a rattle knocking sound that comes and goes mid itle to 1/4 throttle.<br />It starts up slowly then increases for a few min. then instantly stops. Then in a couple of mins. in will start up again. Peformance is great.I have run it many hrs this way.[so think it is other than a rod ???]<br />What could be loose ?? Sometimes it sounds like in the exhaust.
 
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