Yamaha 4 stroke over rev protection

[Kanadakid]

Rod /JB Any of the techs. what does the over rev protection sound like on 90 / 4 stroke ?<br /><br />It is either the over rev or air in the impeller houseing / jet.<br /><br />Thanks<br /><br />Kid

 

[WillyBWright]

Re: Yamaha 4 stroke over rev protection

Sounds like a misfire at full throttle or anyplace it hits the limiter.

 

[rodbolt]

Re: Yamaha 4 stroke over rev protection

actually its usually quite smooth. at over rev its cuts ign to 2 cylinders but its not as violent as two strokes. the rev limiter should come on about 6200 RPM. but it will be a definate misfire. what RPM are you haveing the problem at?

 

[Kanadakid]

Re: Yamaha 4 stroke over rev protection

This is the engine that has low RPMs at WOT. Outboard jets sent me a 3rd impeller to see what that did.<br /><br />The RPM on the tach we up to 5400 RPM but the spped went doen 3 / 4 mph. But upon taking off the engine made sort of a muffeled / farty noise. Reminded me of anit lock brakes when they oulse in the snow, sort of. <br /><br />If it is the over rev protection the tach is not accurate. Or it could be the impeller is too small and its sucking air.<br /><br />It is one of the two.<br /><br />Thanks for the help guys.<br /><br />Kid

 

[Triton II]

Re: Yamaha 4 stroke over rev protection

Sounds like the impeller is ventilating. Have you checked the clearances between the impeller and the liner as they have to be pretty tight. If the tach is accurate you shouldn't be anywhere near the limiter. Most jet drives can run to 6000 rpm + with out ventilating if the clearances are within limits... the Kawasaki STX-15F jet ski makes 150+ horsepower and runs to 7500 without a reduction gearbox so you should be able to run the 90 up to 6200 without problems. Trouble is, if you do with a worn/undersized impeller it'll very quickly get worse.

 

[scout99]

Re: Yamaha 4 stroke over rev protection

from past experience on my suzuki 90/65 jet i have found that you should not go full throttle from idle rather go half to make sure you have a good water flow with no air mixed to help keep that impeller turning with resistance. This may also help with your over-rev protection. My kicks in around 6200 also