"Woods" jetting for an RM250

[know_fear]

I'm helping a buddy set up his '91 RM250 for tight woods riding. He's new to the sport so the mellower the better. The bike has an FMF pipe and Steahly flywheel weight but I don't believe there have been any internal engine mods done. Are low tension reeds available for this bike?
The carb is currently as follows; Mikuni 38mm,Pilot-35, slide-3.5, needle-6AEL1-60 (clip 2nd from top), main-340. At sea level, 55F it has poor throttle response and no power at lower revs and will spooge even when run at higher revs. Pre-mix is Yam 2R @ 40:1
It will idle nicely but seems way rich at around 1/4 throttle. Has anyone gone to different slides and needles? We need some info to get a starting point.
The cylinder seems fine when looking in from the exhaust port but should we change out the single piston ring before experimenting with jetting? Compression checks show 165 PSI.
Thanks in advance for any information.

 

[know_fear]

Come on guys. Someone must have some hints for jetting.

 

[motometal]

Your compression sounds pretty low for a 250.

On jetting, you have a choice...."correct" jetting or "sluggish" jetting. You could purposely jet it rich, other than a possible fouled plug and more gunk in the motor and pipe, probably wouldn't hurt it any. As far as I know, "woods" jetting isn't any different than "mx" jetting....

 

[Hucker]

165PSI?? Wow, thats really low. After my top end rebuild and 6 months of riding I was pushing close to 215PSI. I'm running mine at totally stock jetting anf for the woods its fine. A 35 pilot seems aweful lean seeing that stock is 50. Mines a bit rich off the bottom end, but a 45 pilot should do the trick. Are you sure your buddy isn't to lean? Keep an eye on the tranny to. Make sure he is running 85W oil, I know on my bike running 75W it would pop out of gear. Also the top end hit on the bike is pretty brutal. Tell him to keep a good grip :)

 

[motometal]

I'm not usually that big of a fan of flywheel weights, but if I remember right that bike would be a prime candidate for one if you want to ride woods. Seems like I remember much stalling, sluggish low end and rippin' top end...

 

[know_fear]

Thanks guys. I'll check the compression again with the engine stinkin hot to see if it's any better. What I meant by "woods" jetting was crisp, clean throttle response even if some horsepower at higher revs had to be sacrificed. Power is vastly overated on the greasy roots and creekbeds we have around here.

 

[Chief]

know_fear,

I have gone a little richer on the pilot, (that's once it's dialed in), It helps reduce the hit at low end. As far as the correct jetting, hopefully someone with a similar year model can get you in the ballpark.

Chief