Yamaha running rough

[geo7]

I have a 2001 15hp electric start four stroke. It starts and runs at the first turn. While idling it is rough. Does not change when warmed up. It goes to full throttle but still seems rough. At full throttle it will run for a while then bog down to half throttle then run a while and stop. It starts right up and it goes through the same process. New gas, new gas line, new gas inlet fitting on motor, carb cleaned and rebuilt, new spark plugs, fuel pump checked, gas filter ok. Can anyone help?
Thanks

 

[Redneck]

Re: Yamaha running rough

I have a 2000 40 hp 4s yammy that does the same thing. I know a guy who has a 2002 like mine that does the same thing.

I am waiting for an answer too.

 

[BruceAML]

Re: Yamaha running rough

What spark plugs are you using? What gap did you use to set the plugs? Have you checked the coil assy? The spark plugs should be NGK DPR6EA-9 set at a gap of .08 mm or .031 in.

 

[geo7]

Re: Yamaha running rough

Thanks for the quick come-back. I pulled the plugs to recheck the gap and they are the right number and gapped right but carbon fouled. I will check the coil assy. looks like they are not firing right.

 

[BruceAML]

Re: Yamaha running rough

Another thought; do you have a Yamaha fuel line assy? The genuine Yamaha line is far superior to any others. Try using one and see if there is a difference.

 

[geo7]

Re: Yamaha running rough

The motor seems to be getting plenty of gas. The coil assy checked out OK. From the carbon on the plugs it looks like the motor is running too rich. There is no carb adjustment to lean it out. Where do I go from here? Thanks for the reply.

 

[Redneck]

Re: Yamaha running rough

I intend on adding another fuel filter between the gas and motor. After reading about today's gas content and the gas trouble I have already experienced I think all should do that at least.

Do some research on the ethanol gas thing on outboards.

I am also going to put mine in the shop again.