this ones for a mate.
he has a 2002 Husky WR250 that is fouling plugs on trail rides. its fine when the tracks are open and flowing, but as soon as it gets tight and twisty and you can't open the throttle up it fouls plugs after about 20mins. plugs are wet and oily. bike runs strong when reved doesn't miss at all and does not blow any smoke. oil ratio is 40:1 Motorex, its been happening on the last 4 rides so cannot be dodgy fuel as fuel was fresh each time.
what he has checked.
carb all ok.
air leaks from magneto side ok. would appear not to be a gearbox side main seal as it does not blow smoke and pulls hard when reved.
reeds ok
no coolant leaks
what we assume its not
electrics as its very easy to start, runs well and will pull 140Kmh in top gear (surely that a good sign of healthy electrics)
piston/bore, as had a rebuilt top and bottom end about 6 rides ago, no problem till recently
Any clues guys?