why is my dirt bike poping out the exhaust and wont start?

[paul h]

i have a 1987 rm125
i start it in gear but it pops and backfires out the exhaust and it wont start
sometimes it shoots flames out the exhaust whats wrong with it

[scionized74]

you are getting too much fuel, try to see if you can reduce the amount of fuel going into the engine.