piston rings

Anyone have any idea what would cause a piston ring to break?..cked compression on my 90 hp johnson mod j90tleor bout 3 weeks ago at dealer and he said all 120 give or take 5 lbs.....he did a link/sys and set timing at idle 4* btdc....went out few times with boat ran great until yesterday ...quit ...took head off and he says looks like broken ring on piston in lower cylinder below #1 ....still ahve 120 copression in other 3....wall has bit of minor aluminum scuff .....no gouges or marks that I can see....going to attempt to take powerhead out remove piston and install anew one....will have powerhead checked.....oh and by the way thank you very much for all the help Ive recevied in here since joining...great resource for people like me

Re: piston rings

Coking is the most likely answer as to what caused the broken ring. What is (was) the top rpm?<br /><br />Try to keep all this with one post. Its a lot easier to follow. (I get confused easily as I try to follow and learn too).

Re: piston rings

top rpm I could reach at wot was 5400....motor seemed to b little cranky to start and get going up to 2000rpm..after that ran like a charm

Re: piston rings

5400 is lugging it. That eventually causes what you see. If you dont change the set up to gain rpm you'll have to decarbon often. <br /><br />The other things you mention suggest dirty carbs. That will certianly contribute to this. And spark plugs. Make sure you use Champions & fresh 87 octane fuel.