I recently purchased an '02 cr250, with stock Mikuni carb. Like the title says, the idle jumps incredibly high when I let off the gas, or when coasting. It doesnt really bother me riding, but it is very annoying. I've never had this problem with any other cr's. 370 main, 22.5 Pilot, needle in 1st clip, air screw 1.5 turns out. I was thinking the pilot may be lean, but turning the air screw in from 2.5 turns didnt seem to make any difference. It didnt happen when I had a 25 pilot and needle in the 2nd clip, but it did have a horrible bog. Any advice is appreciated, thank you

Your pilot is really lean. Should be 30 or 32.5. http://www.procircui...specs3.htm#2002

Edited by Keith72, 06 August 2012 - 01:03 PM.

Keith72, on 06 August 2012 - 01:02 PM, said:

That makes it run like a pig. Seemed like it ran too rich even with the 25. I run this same jetting in my '07 with no problems. Only difference is stock pipe on '07.

VE290, on 06 August 2012 - 01:51 PM, said:

Are you riding at a really high altitude? Maybe your float is off.

Keith72, on 06 August 2012 - 02:24 PM, said:

6,000-12,000 roughly. I set the float height to be level with the pilot jet, as the carb constantly leaked when I first bought the bike. Where should it be set at? The manual wasnt too clear with this.

VE290, on 06 August 2012 - 04:52 PM, said:

The float height is 15mm measured from the float bowl mounting surface to the top of the float with the float just closing the float needle but not compressing the small plunger in the needle. That explanation probably didnt help. Made sense in my head though. lol If you look at it really close as the needle closes you will see what Im talking about.

As for your altitude that small main jet makes sense now. A 25 or 27.5 should work.

Keith72, on 06 August 2012 - 05:02 PM, said:

I can understand what your saying about the needle closing in the seat, but you lost me at "float bowl mounting surface". 15mm from the bottom of the bowl when the needle is completely seated? If so, how do I measure that anyways? I noticed there is a tool for measuring the height in the manual. But if anything, I think my float would be too high, because it still leaks on occasion.

I really didn't have good results with the 25 pilot. There was definitely noticeable hesitation, so I'm reluctant to go back to it. And the 370 is what I'm currently running, I drop to a 360 often.

Could lack of ventilation cause this problem? The TMX seems to vent too much causing hesitation. Sort of hard to explain, but basically I rerouted the vent lines so the two on either side tie in immediately. I did the same on the '07 with good results, and something similar on my '01.

VE290, on 06 August 2012 - 05:28 PM, said:

The float bowl mounting surface is the bottom of the carb with the bowl off(the gaskets surface). The part the bowl mounts too. If you have the carb upside down the float and jets would be sticking up from there. You measure the float height from that point to the highest point that the float sticks up. Its best to measure the float with the carb held at an angle so the float just touches the float valve then it closes. If you search youtube float adjustment you should be able to come up with a video the would help you.

What do you have the vent lines tied into? There are 2 that face up. They each go up and curve over the carb then go down and should be long enough to reach below the frame of the bike passing between the frame and the shock spring. There there are 2 that point left and right out the side of the carb. They should also travel down below the frame. They should not be tied into anything. If your carb cant vent properly that may be part of the problem.

Have you cleaned it recently? Jets plugged? Varnished from old gas? Is your idle set too high? Dose it surge when idling?

Edited by Keith72, 06 August 2012 - 05:56 PM.

Alright, thanks for the info! I will set the float height properly, it is probably off. I have each vent line that point upwards tied into the the vent that sticks outwards on the corresponding side with a T fitting. Its sort of a new system I'm trying, and it worked fine on the '07. In the past, I would just loop the two vents that face up into each other and leave the side vents alone, with the pre '02 engines.

Everything is cleaned, Jets I just put in, perhaps bad pump gas? but not old, idle is as low as possible without dying, and no surges.

Nothing is even out of the ordinary aside from this. Runs fantastic. Its a very low hour bike, original piston still has good compression. I considered the thought that I may have an air leak, but I cant imagine that being the case on a bike with such low hours. I'll adjust the float and hopefully that will solve it.

If that carb is working correctly, and you leaned out your jetting,your right crank seal is toast. Air test the motor

robfromga, on 07 August 2012 - 02:53 AM, said:

Are there any other symptoms of a bad right crank seal? I find that hard to believe, considering the low amount of hours on the bike.

VE290, on 07 August 2012 - 07:17 AM, said:

Anything is possible. And its fairly easy to do a leakdown test.

Is it a boggg when you crack open the throttle.  If it is that is a lean pilot.  Or to big diameter needle.  It does seem like your are fairly lean even for your elev.  Maybe you are leaning out the motor to offset the tranny oil it may be burning.   then after being on the pipe the motor is cleared out from running hard.  then you get off the gas and the lean pilot is making your bike have high idle or surge.  I would be looking to see if any tranny fluid is missing.    just my two cents.

I am having a similar issue with my 03 cr250 i get on it and go through the gears and im getting a rpm (pop) jump ever few seconds then it goes back then it jumps up like surging when I am decelerating from 3 and 4th gears basically does it in every gear but its not as noticeable when im in the trails but in wide open fields its annoying

wrwot, on 12 August 2012 - 03:19 PM, said:

Let me know if you solve the problem. I haven't had any time to mess with mine yet, let alone ride it.

All I did was turn my idle down some and it seemed to help I might look at the air screw as well, but it barely does it at all now, still may consider the jd jet kit for $70 or the pwk carb from eBay

All I did was turn my idle down some and it seemed to help I might look at the air screw as well, but it barely does it at all now, still may consider the jd jet kit for $70 or the pwk carb from eBay  btw u have v force reeds fmf sst pipe and stock silencer

wrwot, on 13 August 2012 - 03:50 PM, said:

You seem to have figured it out. An idle that is set too high will cause surging and a hanging idle. Ive said it before but no one seems to listen.

Keith72, on 13 August 2012 - 04:05 PM, said:

X2.  Exactly what I was thinking when I saw this thread.  Start with the easy stuff.

yea it was the idle and air screw they needed tweeked took 5 minutes and the problems gone