89' XR250R carb jetting component questions

Hi everyone,


I have recently been given an old 89' XR250R to get going for a friend and I have a few questions.

Attached is a picture of the carb (before I cleaned it, had been sitting for years) and I would like to know what each jet/needle does in the overall context of the air/fuel mixing process.

I have got the bike running but the tuning is doing my head in as I don't really know what each screw does and how it affects the bike.

I have numbered the items so hopefully will make it easier for people to respond.




Any help would be greatly appreciated.




1 is the fuel adjustment for your idle mixture. Backing it out makes the idle richer.  You can unscrew it all the way and take it out so you can clean the gas passageway with carb cleaner. Watch the small parts that come out with it like a spring, washer, and rubber O ring. Typical setting would be backing it out apprx 2 turns after you screw it all the way LIGHTLY until it won't go in anymore.


2. is the pilot jet and using the slot to remove it you can change it for another size, but you'd just want to take it out and clean it and the passageway underneath it


3.is the main jet/high speed jet that screws into the long brass needle jet


4. is the Seat for the float needle with its pointed tip that would seat into 4. when the float bowl is full of gas thereby shutting off the flow of fuel into the float bowl


Your carb is essentially the same as just about any other motorcycle carb, so there's plenty of info online about its parts 

Edited by ViperGTS

Thanks for the reply! I have since done further reading and watched a couple of YouTube videos which have helped me figure it all out. Thanks for taking the time to respond.

Now it's just a matter of putting the theory into practice.

If the bike is stock, OR if it was modified and rejetted correctly, the most you'd have to do is make sure all the orifices are clean. Then set your idle mix screw out apprx 2 turns from all the way in and adjust when it's warmed up and idling for the highest idle rpm/best throttle response etc.


So  don't plan on having to make a lot of change/adjustments etc

The carb is a Keihin PD series so jetting issues and cleaning will be the same as the CRF230F and XR200.  The XR200 carb connects the cable directly to the slide and doesn't have the decel enricher, but otherwise works the same and uses the same family of  jets. 

#2 is not adjustable.  My advice is to replace it with a new jet probably a #40.  This jet is for starting and idling and can get destroyed with crud when sitting for an extended period.


The passage that feeds #1 needs to be clear and the o-ring, washer, and spring need to be properly installed.  #1 fine tunes starting and idling.   Two turns out is a good starting point.


Also, replace the float needle.

Bike is running good now, ended up with some dirt in the tank coming through and choking it up again but thats all sorted.

The o ring on the mixture screw has perished so I took it out but the thing is its running fine without this o ring in.


Is it really necessary for this o ring to be in?

Bike is running good now, ended up with some dirt in the tank coming through and choking it up again but thats all sorted.

The o ring on the mixture screw has perished so I took it out but the thing is its running fine without this o ring in.


Is it really necessary for this o ring to be in?


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