I have a 1990 yamaha yz250 it runs then dies and wont start?

Question

ok i have a 1990 yz250 the bike used to run good, but now for some reason it starts but assoon as it gets warm like a couple of minutes it dies and doesn't start. we pulled the spark plug out after it dies to see if it has any spark, and it didn't afterwards but it did before..what would the problem be? coil?

Answer 1

simplest things first, install new spark plug and check for possible lead wire breaks, plug cap, kill switch shorting out, check coil.

Answer 2

piston rings worn, if you war lucky, piston worn if you are still lucky, cylinder scratched if you are not quite so lucky and don't take cleaning your air filter too serious

cold it has some compression, barely enough to run

once it warms up everything expands

and that bit of compression is gone *pffft*

a new top end is routine maintenance for smokers as well as for modern 4-strokes, nothing to worry about

Answer 3

The coil,pickup or magneto.