F115 plugs fouling

[empty shell]

I am having trouble with plugs fouling out when at higher rpm's. When I take off wot motor only last about s couple minutes then startes running bad. Change the plugs and it fine till try wot again. If i stay at lower rpms it will run forever and not foul them. It seems to be fuel fouling them as they are real wet when pulled after motor acts up. Any ideas on what could be problem?
Thanks

[robert graham]

Just curious, how old is your fuel?....maybe contaminated?....

[captain rednut]

fuel

Low octane fuel will give you the same symptoms

[empty shell]

Fouling

Fuel is new. Gas doesnt stay ling in tank as i burn about 20-25 gallons a night about 2 to 3 times a week. I use only ethanol free but it is the cheapest grade they got, however it is what i been using with no problem for uears now

[99yam40]

measure peak voltages at the different RPMs to make sure all charge coils are in spec

Have to make sure they are producing the voltage needed, but I am assuming this motor has them