Yamaha 99 90hp Stall

[yamaha9990]

I may be making some progress, but could still use some objective advice.
Bought it used, no problems reported. Died on first trip out. Maybe out of gas.

Thereafter, stalls in neutral and when pushed into forward. When can get revs to 12000 ok. Ruins great at speed. Have changed fuel/water sep, fuel filter and plugs. Had the carb pilot jets sprayed with carb cleaner.

Local shop says carb rebuild necc but only 50/50 chance of improvement. Also said that carbs no longer made by Yamaha and unavailable.

Have shocked with Ring Free and some other additive. Perhaps slight improvement. Seems to run better when red choke under cover is employed.

Should I try to continue with additives and hope it will clear? Anyone with experience with this.? Trying not to waste money on a lost cause. Thanks!

 

[99yam40]

Re: Yamaha 99 90hp Stall

Pull and clean carbs properly , just spraying will not do necessary cleaning of passages. If you run it lean it will eat pistons.
12,000 RPMs not good on motor

I would not believe carbs are not available anymore for a 1999 model, check online to see if you can order if you have the need, Usually just clean unless there has been water sitting in them and all corroded.

Make sure your compression is still good if you have been running lean for awhile you may have already toasted a piston and then may not be worth the trouble

 

[robert graham]

Re: Yamaha 99 90hp Stall

Same exact motor as mine and it sounds like the carbs need to be removed and cleaned. The jets are very small and once plugged, additives just can't get in there to clean them(additives are mostly preventive). Try draining each carb onto a clean white rag just to get an idea of what's in each one. Good luck and let us know how you come out on this!

 

[yamaha9990]

Re: Yamaha 99 90hp Stall

What does "running lean" mean exactly? Why is 12000 RPM harmful? Thanks

 

[robert graham]

Re: Yamaha 99 90hp Stall

Lean fuel mixtures can be rich, lean or just right. Rich is more gas and less air, while lean is less gas and more air. Lean can cause the motor to run hot, to the point of burning holes in pistons, etc. A plugged carb jet can reduce fuel flow and create a dangerously lean condition,not to mention poor running. A rich mixture will cause smoke, carbon, fouled spark plugs, poor running, but will not ruin a motor as quick as lean. Your 90HP 2 stroke motor is designed to operate at a maximum of about 5500RPM's, maybe 5800, but that motor probably has a rev-limiter on it for around 6400, but it would self destruct long before it ever got near 12,000RPM's. If your tachometer is showing 12,000 then it's out of calibration and needs to be adjusted. Good luck and let us know how it goes!

 

[yamaha9990]

Re: Yamaha 99 90hp Stall

Thanks for info. I meant 1200 not 12000!!!!

On my Yamaha 90 I have had to put the red switch under the cover in a horizontal position compared to vertical.

I thought that would make it richer, but probably am wrong considering what you said. Am I right.?

Someone else suggested putting anti ethanol additive right in fuel/water sep. When I cleaned the small filter inside the engine there was a white creamy material in there.

Still trying to beat this back before bring on a mechanic

Thanks very much for the help!

 

[99yam40]

Re: Yamaha 99 90hp Stall

according to the owners manual the red lever put to the open position is for starting the motor and when the prime start system is not functioning properly, once the motor starts then you are to switch it to closed.

If you have to run the motor with it in the open position then your carbs passages are plugged and you need to fix before you ruin the motor.
Sounds like you need to make sure the tank and all lines are cleaned also if you have white stuff in the filter