he says its a Margay with a Yamaha KT100 2 stroke motor he says it needs a new piston how does this kart look he wants to trade for a dirt bike or atv also how hard is it to find parts for this motor
Yes. The KT100 is a durable, reliable and rugged engine. It puts out about 15 hp. A new KT100 runs ~$750. Instead of just a piston, you may want a full, top-end rebuild. However, Comet charges $400-600 for that. Can't beat a Margay kart. But, you need to make the final decision as to how much whatever you are trading for it is worth to you.
Margay spindles, yes.. Margay kart.... uhm I doubt it.
Check for the serial number (and yes it MUST have one)
if you can't find a number, it's for sure not a Margay, and very likely NOT race legal at all
(otherwise there is at least a FIA homologation number)