I am new to forum and having a real problem figuring out how to fix a loud exhaust on a fresh water run 02 Yamaha 15 hp 2 stroke, model 15 MSHA. The noise got worse at low idle and some exhaust leaks out of the lower cowl on forward side and does not seem to come out of the upper exhaust opening on lower cowl as much as in the past. If I push the motor lower into the water the exhaust noise is less but still more than normal.
I pulled the power head and replaced the exhaust manifold gasket, I could not see any cracks in the exhaust manifold, there were some signs of discoloring on the painted manifold due to heat. The old gasket did not really appear to show signs of major exhaust leakage but possibly some, it was hard to tell, the bolts seemed tight but not over tight when removing, I really thought the gasket was the problem but a new one did not fix the noise. It was and still is also louder than normal at full power and has now lost some top end power after reassembly, at first I had the throttle cable out of adjustment but re set it and the butterfly on carb opens up fully, the other levers and controls attached to throttle seem to function ok.
Can anybody suggest where to look next ? Cracked block?
I pulled the power head and replaced the exhaust manifold gasket, I could not see any cracks in the exhaust manifold, there were some signs of discoloring on the painted manifold due to heat. The old gasket did not really appear to show signs of major exhaust leakage but possibly some, it was hard to tell, the bolts seemed tight but not over tight when removing, I really thought the gasket was the problem but a new one did not fix the noise. It was and still is also louder than normal at full power and has now lost some top end power after reassembly, at first I had the throttle cable out of adjustment but re set it and the butterfly on carb opens up fully, the other levers and controls attached to throttle seem to function ok.
Can anybody suggest where to look next ? Cracked block?