idle problems

[mopar]

i have 89 yz 250 and the engine has a bad idle and take off, it surges and dies and needs the choke to be started even when warm, could the idle jet be too lean?, it has a full fmf exhaust and the enigne had been rebuilt with all new seals, psitons and connecting rod.

 

[CRguyStan]

Sounds like the pilot is too lean, but first I would pull it and make sure it is not plugged up. Also check the air screw, try turning it all the way in, then back out 1-1/2 turns after cleaning the pilot.
Stan

 

[mopar]

thanks, would a leaky joint in between the exaust pipe and muffler cause any problems?

 

[TimberPig]

You're lean on the low speed circuits, likely a plugged pilot jet, or a pilot that is too small.

As to a leak at the pipe- silencer joint, it won't hurt anything, other than leaking oily residue all over the bike.