ok guys the reason i thought it was something to do with the flywheel this beta was kicking out 5-6 volt on tick over. i got a 02 beta aswell.so tested that and got 8-9 volts. so i took the fan off the problem bike. ran it on just 3volt for 10 mins and all ok fan worked fine.untill i put a heater on it.yess the fan nearly stoped. £130quid later all good. so i took the old fan apart. the whindings conecting the power had burnt out but not totaly so yes it would work until it got warm then stop. well atleast the elictrics are good on this bike now.lol thanks guys