yamaha tech help please!!

[gunner1938]

I have a 2001 225 v-max ox66 that is fouling plugs every day I use it. The plugs are black and wet, the o2 sensor is also wet. It runs rough with the knock sensor hooked up,and it is slow on top end speed. I have had a lot of parts replaced already with not much success. This is what I have had done. I have replaced the lift pumps,o2 sensor,knock sensor,fuel filters and cleaned and calibrated the fuel injectors. The dealer also checked the t.p.s. sensor ,the oil linkage, fuel pressure and a leak down test. Any ideas? Thanks, Jason

[Stratos21]

Sorry I see you have replaced the o2 sensor.....sorry

[Phoenix721]

I had A similair situation that no dealer could figure out.(5 different ones) Yamaha sent their local tech to check it out and found a tiny piece of rubber from the inside of the fuel line that was stuck on the needle of the float in the VST which was prohibiting the float from being able to shut off the fuel when the canister was full. The excess fuel then is routed to the cylinder vent lines and creates an excessive rich condition due to the raw fuel. Hope this helps.