Trx250R jetting help!

[lisnup65]

I know and understand that jetting cannot be done via internet forums, but I would like an idea what others think on where I should start.

Machine history is really unknown.
What I do know!

Fresh top end at 1.00 over(68mm)
New Boysen reeds
PSI exhaust
FMF Q series silencer
stock carb
Uni airfilter with outerwear air box cover and factory airbox lid w/ holes


The machine started and ran before motor removal. It pulled good and hard, but it would flutter after coming off 3/4 to full throttle. I would need to nurse the throttle to keep it from bogging out completely. While at 3/4 to full throttle she was fine, and the same goes for the rest of the range. It was just when coming down.

That may contribute to a leaking main crank oil seal.

Anyways here is what the carb is currently set at:

Needle 4th clip as called for in the manual
162 main where as stock calls for a 150
58 slow where factory was a 48

I have fouled a total of 2 plugs with only around 3 hours of total run time. The oversized main may explain that!!!


Thoughts on a good starting point?

[deathman53]

lean jetting, I'm guessing you have a pipe, go with a 170 to start. I could be wrong, but 162 seams lean for a 80 over motor. most 80 over 250r's with a pipe run atleast a 165. What are you mixing the oil to? if you are mixing 20:1 that probably is the cause of the fouling. us 32:1, 4 oz to one gallon.

[deathman53]

also the often forgotten item, what is your needle clip at? and what needle?

[lisnup65]

Stock needle(4th clip as said above), 50:1 Blue Marble.

I am thinking its rich and not lean!!!!!

Here are pics of the plug I fouled along with the good plug from when I pulled the motor.









They both look rich 2 me!!!???

[deathman53]

yes, they do. i've been told that at higher elevation you use smaller jets, thats why a bike jeting in CA, will never run right in NJ. do you have the airbox lid on?

[lisnup65]

yes, they do. i've been told that at higher elevation you use smaller jets, thats why a bike jeting in CA, will never run right in NJ. do you have the airbox lid on?

Lid on with a bunch of holes and a outterweat on the ox. Sorta under the lid. So water and large debris cannot enter the box.

[x.system]

I would leave it the way it is and do a couple plug chops with a new plug. That will help determine where or what to change. Try one at half throttle then again at wot.