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I have a F115 (80HP) Jet motor mounted on a Sea Ark 1872 Jet Tunnel center console boat. I am concerned about loosing aprox 400 RPM and about 5 MPH at WOT. About 50% of the time when getting on plane the boat/motor will accelerate to 30MPH at 5300RPM, ( I am pleased with this performance) and after approximately 1 minute at top speed the engine will drop to 4900 RPM and speed will drop to 24MPH. The other 50% of the time accelerating to plane the boat/motor will not get over 4900 RPM and speed will get to 23 / 24 MPH. Will struggle to get on plane with 2 people in the boat. As soon as I expierence the loss in RPM I can immediately feel the boat start to slow and it feels as if it was under a great strain. I have changed plugs twice, no visable water in fuel, One dealer tells me there is no computer on this engine to check diagnostics, Yamaha representative said the motor can be hooked up to a laptop. One dealer could not duplicate the problem, I have tried it since and the problem still exists. Any suggestions will be greatly appreciated. Thanks in advance.
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Jet drives on Tunnel boats have to be tested on the water in order to diagnois problems and would be hard for me to say what the problem could be. I have rigged jet drives on the Sea Ark tunnel boat and it works well togather, engine height is very important. The F115 engine does have laptop connection inside the elect. box on engine and it would help to run the computer diagnoistic to see what the engine is doing. -
Thanks for the response,Comment
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