Yamaha 2004 F50 4 Stroke - Wants to stall on acceleration & runs rough/mis-fires

Hi All

My pontoon has a 2004 Yamaha F50 4 stroke engine. The engine started up and idled fine, but when I went to give it some gas the engine sounded like it wanted to stall. This is when it's not in gear. I had to feather the throttle up to get it to go to higher RPMs.

It was also running rough and mis-firing a bit under load (in gear and cruising at around 2000-3000rpm - hard to know exactly as the tach is not working either....that's another problem).

I thought it may have been bad gas or may have got some water in the gas (the tank was at <1/4 full and was in there all winter - I did use Sta-bil when I winterized it). I put about 6 gallons of new 93 octane in it and also about 6 oz of Heet to see if that would clear up the issue.

It didn't.

Still have mis-firing and runs rough at 2500-3200 rpm while in gear.

Do you think it still could be the gas that's in there or do I have something else I need to look into?

Thanks for the advice.

Hi 101mph,

Did you get to the bottom of this issue wit your Yam?

I have very similar symptoms - any help will be gratefully received.

Thanks, Rob

robfnet said:

Hi 101mph,

Did you get to the bottom of this issue wit your Yam?

I have very similar symptoms - any help will be gratefully received.

Thanks, Rob

Click to expand...

It was the carburetor being a bit gummed up. I was fortunate to only have to run about 3 bottles of Techron fuel system cleaner at "triple dose" concentration and not have to remove them and clean them out. After running the Techron thru it, all of a sudden it was like a light switch turned on....at 2400 rpm the engine was running rough.... then smoothed out and purred like a kitten.