'89 Yamaha 150 2 stroke racing in idle

[Afinelli]

I have a 1989 Yamaha 150 HP two-stroke on my Outrage 18. Generally it has been running fine ? until this weekend it suddenly began racing at around 2000 rpm with the cable control arm in the neutral (idle) position, and I couldn?t get it to calm down except to basically kill it with the manual choke or the ignition switch. I checked all the linkages inside the engine and could see that the throttle arm is being moved through its entire range of motion. I also adjusted the throttle screw stops and exercised the throttle and associated linkages manually just to be sure there wasn?t any more room for movement in those mechanisms. I ran the engine sufficiently long in my opinion to negate engine flooding on start-up as a possible cause. Its as thought the engine is being permanently flooded -- or like being in a car with the accelerator pedal stuck (even though I know the Yamaha engine throttle itself isn?t physically stuck out of idle position). I let the boat sit over night and encountered the same problem the next morning.

Boat is at a slip so I was reluctant to try putting it in gear with the engine racing ? for fear I wouldn?t be able to control the boat in tight quarters. Only other possible related factors I can add are (a) the engine has been taking longer than usual starting up recently, and (b) we?ve had lots of rain here in New England throughout the month of June and I?ve only been able to use the boat twice before this episode developed.

Anyone have any idea what may be going on. Is there something obvious I?m missing?
Thanks,

 

[UncleGrady]

Re: '89 Yamaha 150 2 stroke racing in idle

I had the same problem with my '88, it was the linkage that connects the throttle to the magneto advance (it's about 2" long and is up near the top carb).

The black plastic end became brittle and broke off, once I moved the advance back to a normal spot, the idle came down but of course, I could not accelerate until I replaced the link.

$4.oo later, back in business.

Good luck.

UG

 

[Afinelli]

Re: '89 Yamaha 150 2 stroke racing in idle

Uncle Grady:
I know the piece of linkage you refer to, and unfortunately, that last piece of linkage is in place and operating on my engine. Thanks anyway for the advice.
Have you had any experience with carb problems? Any idea what it costs to service/rebuild carbs on this vintage/HP Yamaha?
Thanks