Hi,
I rode the bike for most the day a few weeks ago and After using it for a few hours it became very hot, It would bog a bit when the throttle was opened and seemed to have less power, the engine smelt hot and the exhaust silencer was too hot to touch. After lunch I refuelled it and it seemed better and didn't get as hot but still seemed too hot. The cooling fan cut in as expected but I've since found there was only water in it and not specific coolant.
I hadn't used it for over 4 months before that so the fuel was probably a bit stale.
I have checked the water pump impellor and all is well, I have the carb off and will clean this, I've taken the barrel off to check for partial seizeing and to check conrod play as I suspected it was running lean. All is ok, bore/ piston good and the small/ big ends are fine. The only thing is the top of the piston is very sooty and so is the inside of the head. I'm new to trials but have mx bikes and I'm used to a browny colour with no soot on the piston crown. I now realise ive been running the oil too strong at 40:1 but the soot build up and hot running can't be down to this. Could it be as simple as stale fuel? how does the vacuum fuel pump work, could it be that?
Any ideas would be gratefully received.
Rob