CRF250R (2005) fuel screw question



I'm looking for some education on the "fuel screw" and proper setting for it on my 2005 CRF250R.


I have been trying to read up a lot and learn myself up on my bike, and how to keep it running at it's peak.  I see a lot of talk about adjusting the "fuel screw" to get the proper idle RPM.


However I am a bit confused as to if the term "fuel screw" is referring to the air/fuel mixture screw, or to the actual idle adjustment screw.


My bike starts right up easy when cold (especially with choke on), with choke off it doesn't idle until it warms up a little bit.  However I noticed that after I'm riding it around for a little while and it starts to really get warm the idle speed will slightly increase.  Seems like once it's fully warm after say 10-15 minutes of good riding it stabilizes though. 


I think this happened because the first time I rode it,  I adjusted the idle speed screw in, prior to it being fully warm, and then once it was fully warm it was idling higher.  So, I adjusted it back out until the idle came back down.  From there it seems like it remains constant.


I don't think it's a hanging idle, but maybe it is.... not sure.  One ride I had to adjust the idle screw two or three times (by like 1/8 - 1/4 turn) because as I rode it more it seems like the idle kept going a little higher.  I finally found a setting on the idle screw to where it remained constant.  The subsequent ride, after it was fully warm it stayed at the same idle RPM as the previous ride.


Another thing I noticed, but at first thought was normal... and it very well may be... is that after I make a higher speed straight pass, say revving it out in third gear, then let all the way off the throttle (chop the throttle), it will "pop" slightly from the muffler.  Also if I downshift and the RPM jumps back up due to the lower gear, it might pop a few times also.  I read that sometimes this can be remedied by "turning the fuel screw out a bit".  The popping only occurs when I go quickly from half or more throttle, to no throttle or like 1/8 or less.  When it happens from downshifting, it is when I'm off the throttle.  Never pops by just slowly decreasing on the throttle.


That's where my confusion is.  Is the fuel screw referred to the idle or mixture screw?

Edited by molonlabe1911

I did not read through your whole post - sorry


Idle screw is on the side and easy to get to.


oem PILOT screw (but can also be called air/fuel mixture screw) is on the bottom and a pain to adjust. It's not something I personally adjust often but I bought a good after market one like this but there are other styles.




On my 05 I can ride in a wide range of temperatures and elevations in one ride so I've left all my jetting stock.


I set the pilot screw to stock 1-3/4 turns out.


Once the bike has warmed up and the choke is off, you then adjust the idle screw to around 1600 to 1800rpm's. I had a shop guy adjust this with a TACH while I was there so I now adjust by ear. I'll adjust it a bit up or down depending on the temperature etc.


OEM service manual or a Clymer is key and gives you all the specs etc.


Hope this answered some of your questions.

Edited by filterx


I use this one its easy to adust as it secures to the side of the float bowl using a supplied bracket, I set mine at 1 5/8 turns out on my CRF250X (XRSONLY.COM)

The good thing about this one is it will not move or fall out due to vibration (vibration will make the bigger aftermarket ones move) IMO

I got the red one like the first poster put up. My local bike shop had it. Now the hard part, getting to the stock one to remove it. How the hell? Can it be swapped without removing the carb?

I had some $20 dollar one that fell out. Then the oem fell out. Then spent $8 on a tusk and have 5 rides on it and it hasn't budged.

To get the old one out loosen the hose clamps on the carb and turn the bottom of the carb towards the shifter side. Then just unscrew it.

also if you have one of those small flat head screwdrivers with the pocket clip like the tool trucks have you can hammer the plastic part all the way down to 1/2" from the tip then cut off the excess metal sticking out the back end it makes the perfect fuel screw no rotating carb or anything

also if you have one of those small flat head screwdrivers with the pocket clip like the tool trucks have you can hammer the plastic part all the way down to 1/2" from the tip then cut off the excess metal sticking out the back end it makes the perfect fuel screw no rotating carb or anything

Ahhh. Good idea! I'll try this.

I got the red one like the first poster put up. My local bike shop had it. Now the hard part, getting to the stock one to remove it. How the hell? Can it be swapped without removing the carb?

I like to remove the subframe and pull the carb, no need to disconnect the throttle cables. The mufflers can stay mounted to the head pipe. Takes less than 5 minutes to remove subframe.

Just make sure you get out the little o-ring from the oem screw. IMO as posted pull the sub-frrame and rotate the carb

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