Questons on 03 250f

recently bought an 03 250f with a yoshimura pipe and powernow. Not sure if its jetted right and it runs rough, doent seem to rev out like it should, or it could be the valves not adjusted,so I plan to ck tonight or tomarrow.

I'm at sea level in south Texas and wonder if someone could suggest jetting settings,It seems rich as the rear fender is black and the plug was too. fuel screw out 1 1/2 turns now as it was closed completely.

I was given a manual with the bike so should i just follow the book on valves?

Have 2 sets of fairly new chain and sprockets from y01 yz 125, do they fit the yzf?

Thanks for the help


If you have the stock pipe, I suggest going back to square one and establish a base line for your jetting. Install the stock pipe and remove the PowerNow and ride the bike. If all is fine with the performance then install the pipe and Powernow in steps. Do not reinstall both of them at the same time. This will take more time, but you will benefit from learning how each of these items affects the performance. When you make the changes to the pipe and valve, make sure that you ride the bike at the same track or wherever you ride so you can make a direct comparison. The pipe is an easy swap and can be made while you are resting and the bike is cooling off. As far as the sprockets are concerned, they probably fit. I suggest that you find an on line parts catalog and compare the part numbers of the sprockets from the old bike to the part numbers of the sprockets to the new bike.

Be sure to check the rubber boots between the carb and the head and between the Powernow and the airbox for cracks. Some people here have had issues with the cracks causing poor rideability. It's cheap to look.

your stock jetting should be real close with your items on.

Your clip pos, IMO,could be moved to one leaner than stock

Those sprockets and chain will fit too.

I have those same bikes in my garage.

Change your gas to brand spanking new premium as well as your plug,and change your oil/filter/oil and Air filter.

Follow your manual on your valves.


My settings for my 03 and yosh pipe, no air cage were: stock pilot jet (size ??), 178 main, needle in middle or 3rd clip, air screw varied with temp but usually 1.5-2 out.

I never fouled a plug and it ran good or at least I thought it was good until I installed the JD Jet Kit. Runs much better now. When testing MJ's with the JD, I tried smaller jets and the bike wouldn't rev, more specifically it wouldn't pull 5th nearly as easily. I went back up on MJ sizes and it would pull 5th much easier.

what is your gearing?

Is your rear tire in good shape?

What is the track conditions your on?

48 rear on a 739 dunlop, mostly dry track with hardpack except on race days. Soon to change to 756 tires.

Think I'll try the jd kit since it worked magic on my ktm.

Thanks guys

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now