Yamaha 150 HP V6 2 stroke outboard dies at full throttle temporarily

[m14stn]

I have a 2002 Yamaha 150 HP V6 2 stroke outboard that I recently had a tune-up and is new to me. When I run it at full throttle for about 20 minutes or so it will cut back and die.
I had fuel service done and it has a new fuel/water seperator. Carbs were cleaned as part of the tune-up.
If I let it sit for 5 minutes or so it will run fine the rest of the way back. I was running premium gas, should I run regular 87?
Not sure what is causing the motor to shut off.
I tested running it lower than full throttle and it seemed to not have trouble. Engine is peeing just fine.
Could this be the trim? or maybe a Thermostat? Any help is appreciated.

 

[pine island fred]

Re: Yamaha 150 HP V6 2 stroke outboard dies at full throttle temporarily

I can think of two things that MIGHT be causing your problem. One is simple, the other you may not like. Many fuel tanks do not have a separate vent and are vented thru the fuel cap, same as that hissing when you fuel up your car. Cap might be defective. leave it loose but secured with some duct tape or remove it completely and see if that helps.
Second, many tanks have a fine mesh copper finger filter installed in the fuel pickup tube in the tank. They get clogged with leaves, acorns, hair all that mysterious stuff that somehow make it into your tank. You will have to remove the anti-siphon valve and pick up tube to get to it. You may have to punch it out with some welding rod from the bottom of the tube. Remove it and throw it away. After operating for awhile the debris will get sucked into the filter, letting it set allows the stuff to fall off only to be sucked back up later. Best I can do for you, hope it is the gas cap. regards FRED

 

[m14stn]

Re: Yamaha 150 HP V6 2 stroke outboard dies at full throttle temporarily

Thanks Fred.
The fuel tank was cleaned and the fuel lines serviced so I 'hope' it is not the latter. I did notice the vent by the fuel tank. It was allowing air in and out but looked like I bumped up against a dock as it was dented a little. Should this vent have a cap? Mine does not.

 

[pine island fred]

Re: Yamaha 150 HP V6 2 stroke outboard dies at full throttle temporarily

The vent should not be covered. Try this. Get a 5 gallon container, disconnect the fuel line after the filter and stick it in the can. This way you have eliminated everything in the fuel delivery system except the primer bulb. Run it and see if you still have the same problem.
Do a good check of all the ground lugs and terminals on the motor. Sometimes they look good but are corroded. While running for awhile, toggle the trim switch. If the motor hesitates, boggs or quits, you have a impending ground lug problem. Sometimes the trim motor and the rest of the engine share the same ground. Actuating the trim system divides the 12 volts between the 2 which will kill the motor. Good luck, FRED

 

[m14stn]

Re: Yamaha 150 HP V6 2 stroke outboard dies at full throttle temporarily

thanks for your help Fred. I will try that. I took the boat out again and it runs great under full throttle for a long time. Is it possible that at full throttle it is just not getting enough gas through the lines?