KX250 spark plug type

[afireinside]

Hi ive got a 89 kx250 with an 83 engine fitted. i've just rebuilt the top end as i bought it in bits. and it seems to lock up sometimes as if theres something stopping the piston moving and it backfires a bit. the guy i bought it from thought the engine was an 89 and had bought the wrong head gasket set for it, so i've put it back together using the correct ones but im worried that he's put other 89 parts on it

i was wondering if the sparkplug could be the cause, does anyone know if the sparkplugs are different between an 83 and an 89?

and also it looks like a fairly new piston so that could be from an 89, again anyone know if theres a difference


thanks