not vmx but 'the joys' of buying cheap crap. a year or more back [probably more] i rebuilt the neighbours kawasaki 50 kids quad using a cheap kit--head-- cylinder with piston kit-- oil pump & all gaskets plus other bits for $69 which still sounds good i suppose but just came back with no compression, always had valve clearance & realised it was getting low on comp a couple of months ago so backed tappets off more & gave it a good rev with crc down the inlet while reving & was better [till now]. Bottom line is exhaust valve burning out & luckily i'd not binned the originals so checked with a magnet & original is 'non magnetic' & this cheapy 'is' 'magnetic. Lesson learnt [probably not], love bargains lol. Bugger--just realised my chinese crank & piston arrived for my husky 61 chainsaw--now i'm worried. Have a good dayyyyy.
