1998 Yahama 150 loses RPM at high throttle

[Rdude]

I have a Yahama 150 two stroke (fuel premixed in tank)that runs fine until I excellerate to high RPMs (over 4000). It will accellerate to top end but will sporadically bogg down off plane. After reving in neutral it will replane but will bog again if over 4000 RPM. (randomly) I have reworked the entire fuel system checked tank and pickup, replaced lines, replaced bulb, replaced water seperator, checked vent and checked fuel filter. Also their is no siphon prevention device evident.
Noticed the bottom plugs were fouling a bit and cleaned them twice now. Only thing I can figure was that I did run some Carbon free through it last year in the keys.
When I ran it on a diagnostic tank it appeared fine however I will try again to make sure it wasn't just a lucky moment.
Any suggestions would be appreciated.

 

[robert graham]

Re: 1998 Yahama 150 loses RPM at high throttle

how long since carbs were cleaned? sure sounds like dirty carbs/jets

 

[Rdude]

Re: 1998 Yahama 150 loses RPM at high throttle

A couple of years ago I had it serviced because the lower carb was sticking and they pulled the carb and freed it and did some cleaning (but no rebuild) Is there a carb cleaner that I can try spraying into the air intakes before I have to get a carb rebuilt?
I pulled the bowl plugs yesterday and pumped fresh gas through. (seemed very clean)
Seems like it trys to pass whatever it is sometimes when running at high RPMS but is unable to do so. Not sure why it would be so intermittant and only appears when under load.

 

[Rdude]

Re: 1998 Yahama 150 loses RPM at high throttle

After pulling carbs and cleaning (and replacing boal gaskets since they tear when removing) I finally decided to change the fuel pumps. Cost $100. It now runs like a top better than ever. Basically I have replaced the entire fuel system.
Will probably need to run through some ringfree since the bad fuel pump was leaking additional gas into the combustion chamber through the mechanical port. Sould have figured this out earlier as the lower left plug was fouling and engine smoking more than usual. Should see some great improvement in gas mileage as well.
Hope this helps someone else.

 

[robert graham]

Re: 1998 Yahama 150 loses RPM at high throttle

glad you got it fixed, and in the process, have probaly become a bit of an expert on the Yamaha fuel delivery system. my motor is a 1999 Yamaha 90C with no problems at all, so far. I've wondered how long the fuel pumps normally last and if I should just go ahead and replace mine, before it fails. Just don't know about that. Good Luck!