2001 Honda CR250 Air Screw Question

Still waiting on the manual for my bike to come in the mail. In the interim, I decided to check my air screw setting to see if there was anything to be gained by adjusting it.

What I find is that the bike is not responding to AS changes. The screw was set at 3.5 turns out from seated as I purchased it. This tells me that the pilot is too large if what I've been reading is correct.

The odd thing is that I can turn the AS almost all the way in and the idle just barely starts to slow. By all the way in, I mean I can get it down to about 1.5 turns out from seated and it will still idle just fine. The bike idles perfectly and starts first kick with no choke. From what I've been reading, you are supposed to raise the idle up significantly while you adjust the AS to keep the engine from stalling. I did not do that but yet the motor does not stall even with 2 full turns in. I was expecting to see the idle speed change drastically during this test and was surprised that it did not happen.

Any suggestions?

Assuming your jetting is stock which is set up rich you won't sense much change during adjustment. On mikunis I never turn the air screw out more than 2 1/4 turns. The idle adjustment screw for the all out racers set up with no idle. The carb works better that way during going into a turn and accelerating out of a turn. I prefer some idle so I can a least put my googles on quickly before the engine stops.

the air screw is most effective from about 1-2 turns out. if you take your airscrew out, you'll see the taper on it. once you go past a certain point its out of its effective range and going much more isnt going to have much effect. you need to use the airscrew to find your highest idle at about 1.5-2 turns out. then go ride the bike and go WOT on the throttle. if it bogs (it should, which is why i like to set highest idle at 2 turns out so i have 0.5 more of a turn in adjustment to richen her up) go in 1/4 turn and try again until the lean bog is gone.

i have a 00-01 manual i can upload if you want the info now. the manual was originally provided by "closedcasket" over at allthingsmoto and is in PDF format. let me know.


Good job on reading and finding info.

To further answer you question.

If your bike starts cold easy, or if you can turn the air screw in more then 1/2 turn and the bike still run, then you pilot is to rich. Make sure your idle (slide) is not to high. You want the diameter of the needle giving you false results while you are trying find the correct pilot size. Try to get a normal steady idle with the slide as low as possible.

Try a leaner pilots until the air screw falls into its adjustment range. Make sure and wait a few seconds in between each 1/4 turn of the airscrew to let the engine get used to the new mixture. Just remember, if the pilot is lean the engine will have a hanging idle or run on when you close the throttle, while riding.

I too set my pilot were there might be just a slight bog when I whack the throttle wfo. I use my air screw to fine tune this. When you pilot is correct the airscrew becomes very sensitive. Between 1-2 turns out.

Edited by Kirkes

Another question along those lines; If I drop down in PJ size, I will also then need to richen (raise) the needle, and/or increase MJ size as well correct? I ask because mid & top end are perfect. It's just the low end that blubbers & stutters until it comes on the powerband.

I will have to pull the carb to see what PJ is in there at this time. I have a local Yamaha dealership right up the road from me. Is it possible they will have jets in stock for my Mikuni carb? If I pull the carb I want to be able to pick up jets immediately and make the necessary changes as soon as possible.



No you won't have to change the needle or main if the mid and top are fine and the plug shows it. The dealership should have jets in stock but some don't have a huge variety of different numbers in stock. Make sure you take your current pilot in with you so they get you the correct one. There are a few different variations on shapes of the jets and I have found even if they can simply look it up in their computer most are to lazy to do so. Might save you a trip if you just take it with you.

Thanks for the information guys. I'm trying to get the bike set up for this weekend as I'm riding with a friend of mine and he has a KTM. He's telling me I should have gone "Orange". I told him no, HE should have gone RED! It's like a sibling rivalry.

I went 32.5 on the pilot, S-8 from the stock S-9 on the nozzle (needle jet). And 410 on the main.

The air screw responded a lot better with the 32.5 versus the stock 35.

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