Jetting

[waynec]

I have 1992 RM250, It has been ported and has Boyeseen rad valves. I have never been able to get a good burning spark plug, it is always oil fouled. When the bike is in gear and clutch held, it breaks up at 1/2 to 3/4 throttle. When riding it runs well in 1-3rd gear, when I go to 40r 5 gear it bogs down. I currently have stock jetting and ignition timing. I use a NGK B8EGV plug

 

[helio]

How many hours with the currently piston ?

 

[Glitch]

I would say move the clip on the needle up one spot and get a bigger size main jet.

 

[waynec]

piston and rings are brand new, thanks for your reply

 

[Rockey5000]

Ya, what glitch said.

 

[oyster209]

i have a 93 rm250 and it sounds like what mine experienced. after much frustration it turned out to be the clutch side crank seal. check your gearbox oil, if its low it could be oil is getting sucked thru the bad seal into your cylinder giving you that oily plug.