took ryan out on sunday for a bit of practice ready for this weekends oset cup.After 5 mins the motor started smoking then just stopped dead, stripped it down there was more mud and crap in there than was on the field, anyway cleaned it all out left to dry for a couple of days then rebuilt last nite everything was working fine till this morning, again 5mins on bike it's started smoking again he's only been on tarmac since. everything looks fine any ideas what it could be?? don't fancy it stopping after a couple of sections and having a bad tempered 4 yr old on saturday