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I have recently purchased a boat with a 1997 Yamaha 115 hp motor. The motor will reach about 3500 rpms and then it hits a wall and will not go pass that. The carbs have been cleaned twice, the plugs changed and we have put on a high end stater. The motor starts fine,idles fine and runs fine at lower rpms. What else should I check?
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lusky,
Make sure all filters are clean.
Check compression.
Check linkage to carbs to see that carbs open all the way with remote WOT.
Check the butterfly choke plates to make sure it they are not partially closed.
Get the motor to max out (3500) WOT and have someone check the primer bulb. If it has collapsed, then there is a fuel restriction from there on back to the fuel tank - maybe kinked fuel line or faulty anti-siphon valve (if you have one) or tank not venting properly.
It the primer bulb has not collapsed, then try pumping the bulb several times to see if the motor rpms pick up - if so then bad fuel pump.
Check the pulser (trigger) coil assy to see that it rotates with the throttle to advance the spark.
Check the spark timing per the shop manual.
Are you sure you have the right prop for the load you have? May be that there is too much pitch on that prop.
Good luck [img]smile.gif[/img] ,
Ken K -
Thanks for your suggestions. I ran it again today and it was the same problem.It starts everytime and it runs perfect at 3000 rpms and then when it gets to 3500-3600 rpms it hits a wall and will not go past it. I don't thinks it's a fuel problem. I will keep trying. Thanks again.Comment
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Ken is right on. Are you sure the motor doesn't have too steep of a prop pitch?
You should have a prop tech check the prop pitch and see if it is even in the ball park. If it runs, starts and sounds fine...Check with the fine folks at Power Tech props. You can find them at the url below and should give them a call.
http://www.ptprop.com/catalog/defaul...th=114_194_210Comment
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