View Full Version : Yamaha 4stroke high speed mystery

rob yonover
04-27-2003, 01:49 AM
" my carburated 80 hp 4-stroke yamaha is losing power at high rpms (over 3500)_relative to the other engine.

white smoke also starts to come out at high speed.

less than 3500 rpm, the engine runs perfectly. perhaps it is some crud in the high-speed jets?

any thoughts would be greatly appreciated.

aloha, rob

p.s. the problem seemed to start after i filled the tanks with yellowish colored gas (as opposed to the usual clear). i checked the separator and no problem there. i added sea foam gas treatment.
the battery also died the day the problem started. i changed both batteries, as well as the spark plugs. they both run perfectly now, except for the one engine at high rpms. "

04-27-2003, 11:25 AM

Take a look at the spark plugs. White smoke can mean you are running too lean or that the head gasket is leaking (steam in the exhaust). If you have water in the cylinders it should be obvious when you look at the plugs. Grey, thick deposits usually indicate water in the cylinder.

If the plugs look normal, then remove the carbs and check them out thoroughly.


Brian Fortner
10-22-2006, 05:40 PM
"05/06 yamaha 90 4 stroke. 25 hours on motor.Went out yesterday, when leaving dock in no wake zone I noticed a weird little noise but it totally dissapeared when I accelerated. Traved about 20 miles various speeds and some fishing involved.When we reached the no wake coming back in the noise was back but this time it kinda sounded like a belt squeeking.When out of gear at idle noise dissapeared after a couple of minutes. Obviously still under warranty, but still; any clues?"