Yamaha 90 2 stroke top end loss of rpm

[DavidG]

2003 90 2 stroke, oil injection - been sitting for a year - idles great - runs great up to 3,400 rpm - will not go any higher when in foward gear under load - In neutral, reverse or on the hose pipe it will go up to 5,500 rpm - no other problems. all help appreciated

 

[chanice]

Re: Yamaha 90 2 stroke top end loss of rpm

2003 90 2 stroke, oil injection - been sitting for a year - idles great - runs great up to 3,400 rpm - will not go any higher when in foward gear under load - In neutral, reverse or on the hose pipe it will go up to 5,500 rpm - no other problems. all help appreciated

 

[chanice]

Re: Yamaha 90 2 stroke top end loss of rpm

2003 90 2 stroke, oil injection - been sitting for a year - idles great - runs great up to 3,400 rpm - will not go any higher when in foward gear under load - In neutral, reverse or on the hose pipe it will go up to 5,500 rpm - no other problems. all help appreciated

if its been sitting for some time the piston rings may have stuck and you have lost compression.
off load this will rev to its max but under load it will loose top end , an easy test is to take the prop off and check forward max revs in water if it hits 5500 unproped then its a compression problem.
there are many products to clear sticking ring problems but being in the uk I dont know the us brands, someone on the forum will know ,all the best and good boating

 

[Ray Neudecker]

Re: Yamaha 90 2 stroke top end loss of rpm

Most likely cause is a fuel restriction. Tearing down and cleaning the carbs would be the suggestion. Common problem where the motor has been sitting. DO NOT RUN THE MOTOR AT MAX RPM'S WiTHOUT A PROP. SEVERE DAMAGE MAY OCCUR. Test compression with a guage.

 

[chanice]

Re: Yamaha 90 2 stroke top end loss of rpm

Most likely cause is a fuel restriction. Tearing down and cleaning the carbs would be the suggestion. Common problem where the motor has been sitting. DO NOT RUN THE MOTOR AT MAX RPM'S WiTHOUT A PROP. SEVERE DAMAGE MAY OCCUR. Test compression with a guage.

 

[chanice]

Re: Yamaha 90 2 stroke top end loss of rpm

ray its obvious from the origional query that he,s had the revs up to 5500 in neut and reverse, but not in forward off load ,that is why I suggested a quick try forward not a long time thrash!

 

[Ray Neudecker]

Re: Yamaha 90 2 stroke top end loss of rpm

He has already done something that can severly damage the motor. Please don't encourage him to do it again. The problem is not going to be diagnosised or repaired by deliberately abusing the engine. Much more likely to at best ruin the bearings and destroy the motor than any thing else.
YOU DO NOT REV THE MOTOR WIDE OPEN WITHOUT A LOAD SUCH AS A PROP.
The symptoms are of a fuel restriction. Time to start repairing while he still has something left to repair. Or at least do the basic tests such as compression or fire.