05 RMZ 250/ FCR

Remove the fuel screw and make sure the o-ring from the old fuel screw is not still up in the cavity. Fish it out with safety wire if it is. Blow out the fuel screw circuit with carb cleaner and compressed air. Put a little anti-seize on the fuel screw threads so it's easy to adjust.

Clean or replace the pilot jet and blow that circuit out as well. The fact that you're needing large fuel screw openings suggests the pilot might be clogged.

Remove the hot start plunger, clean it all out and put a light coat of grease on it. Ensure it moves freely and returns to fully closed and there's a bit of play at the lever. If the plunger gets gunked up it will stick and make the bike lean.

Remove the leak jet and clean that and the accelerator pump nozzle circuit well.

Make sure the carb cap seal is not leaking and sucking air.

Check the intake boot to the head and make sure it's not rotted or cracked and sucking air.

Make sure the plate on the front of the carb slide is installed correctly. On some FCR's it's possible to install upside down and the bike runs like crap.

These are the common things.

Here is a jetting suggestion OEM and ProCircuit. MJ, PJ, Needle, Clip, Fuel Screw, Slide , Leak


RM-Z250 162 45 NLCT 3 2.25 1.5 40
Pro Circuit 162 45 NLCT 4 2.25 40


Make sure AP is squirting properly, the slide and slide plate rubber gasket are good and you might as well replace the midbody gaskets.

I would recommend a full carb rebuild. I would get a replacement “mid body” o-ring rebuild kit along with all the replacement o-rings in the carb (accelerator pump, fuel screw o-rings etc). I’ve been doing a lot of FCR carb cleans and I’m finding that if they are older than 7-8 years, the mid body seals and orings are shot and block the pilot jet/fuel screw orifices. Regardless of how clean the jets are, the bikes would stumble and hiccup when you ran them through the throttle range. They ran fine up top but the low to mid transition was horrible.

The mid body seal replacement kit is like $30 from All Balls on Rocky Mountain. If I have anyone bring in an FCR for a carb clean, I always replace them. While your at it, I’d get a new carb intake manifold as well as it’s probably dry and cracked. After rebuilding the carb, spray contact cleaner through every circuit in the carb to verify good flow. As mentioned before, check the obvious (valve clearance, hot start slack and seal). Those first generation Kawasuki 250f’s can be a little finicky. Good luck!

Check your slide as well. They do wear out and will make them run like crap. I had a head scratcher with my 05 Kawi and finally settled on replacing the slide plate. Boom, problem fixed.

One of the few 4 strokes I’ve ever raced was a 05 RMZ 250, from new it ran a bit like you describe. Seems like I remember the trick was to go to a smaller leak jet.