Yamaha 150 will not rev past 1700 RPM

[shakerman]

I recently rebuilt the powerhead on my 1988 yamaha 150 . At around 1800 RPM it starts missing bad and will not rev past 2100 RPM . I did a compression test and had between 145 and 150 psi on all cylinders . On the water if you shut the boat down and let water drain from block then restart it the motor will rev up to about 4500 RPM and then quickly fall off back around 2000 RPM . It is getting plenty of fuel . Can someone please help me diagnose the problem before I pull What little hair I have left out ?

 

[rodbolt]

Re: Yamaha 150 will not rev past 1700 RPM

why was it rebuilt? if you did not correct the reason for the first failure it will fail agaain. a bad piston is a symptom not a cause.<br /> check the spark plugs for signs of water. if its not getting water in a cyl its most likly spark or fuel. test the high speed charge coil. then test the fuel pumps and fuel supply.

 

[shakerman]

Re: Yamaha 150 will not rev past 1700 RPM

Rebuilt powerhead because oil injection failure caused piston to burn up. Engine is getting plenty of fuel.

 

[shakerman]

Re: Yamaha 150 will not rev past 1700 RPM

Now I premix fuel and oil. Carbs have been cleaned and are working properly.Previous owner had gotten water in oil tank.

 

[Flybye]

Re: Yamaha 150 will not rev past 1700 RPM

What did you do with injector system? Sounds like you might be stuck in safe mode .

 

[shakerman]

Re: Yamaha 150 will not rev past 1700 RPM

I used a different block that had injector pump and passages plugged off. Safe Mode ?

 

[Flybye]

Re: Yamaha 150 will not rev past 1700 RPM

Sorry i didnt get right back to ya . Safe mode kicks in when oil level drops in oil tank. rpm is restricted so it can limit damage if you run out of oil . If tank is still there make shure its not low on oil . I still have to confirm this from the manual. I will let you know when i do.I am on holidays right now till next week . Keep us posted if you get it fixed

 

[Ray Neudecker]

Re: Yamaha 150 will not rev past 1700 RPM

Disconecting and removing the oil module will keep it out of the safe mode for the oil injection removal.

 

[rodbolt]

Re: Yamaha 150 will not rev past 1700 RPM

how can you say that water in the oil tank was an injection failure? that was a maint failure and an owner neglect issue. but as long as the tank sensor is dissconnected and the oil control module removed it eliminates oil alarms. a true oil failure will usually take out the crank. did ya rebuild or replace the fuel pumps as well? try running with the airbox off and spraying pre-mixed fuel into the carbs. if it picks up its time for fuel pump and carb maaint. also test the high speed charge coil and the CDI output at the problem range.