Idle & Air Screw ??

[Broken Wrist]

Hey Guys,

I need carb help. I bought a 2002 KDX200, FMF Pipe and Airbox cover removed, the bike is in really good shape overall. It ran a bit lousy and had been sitting so I figured it would be best to start fresh. I replaced piston, rings, checked the power valve, new base and head gaskets, new reed valve, cleaned carb, carb rebuild kit, Jet block o-ring, and installed new stock jets as a jumping off point. I went to follow the jetting guide here but my air screw and Idle screw do almost nothing. I can stall out the motor by installing air screw all the way in, other than that the bike just idles normally.

The compression is good and bike starts first kick. I do not currently have the stuff needed for a leak down test, so I haven't done that yet, but my question is does anyone know why the idle & airscrew has little to no affect ?? Thanks !!

[KDXGarage]

What is your altitude, temperature and humidity? It is super hot here, so stock jetting would be really rich around here.

[Broken Wrist]

Thanks for the reply KDXGarage,

Today it's 114 degrees - Haha. Altitude is about 400 feet, I'm guessing humidity is almost zero.

I have a little more info, the bike will just barely idle with the idle screw fully turned in, and the slide is opening as I believe it should with the idle screw moving in and out. I have the airscrew set at 2 turns out but I really can't get a change in RPM's by moving the airscrew.

My next move was to start dropping the pilot. Could it really be running so rich with stock pilot that the Idle and Air screw won't work??

Thanks again!!

[KDXGarage]

WOW!! 114!

I would go down 2 sizes to start with. Just be sure to use official Keihin parts, not aftermarket. A few people have not had the best of luck with non-Keihin parts. With it being that hot and the stock pilot, the air screw won't have any effect. The pilot jetting has to be at least in the neighborhood before it will start having an effect.

I would get the pilot and air screw right before moving on to needle thickness and height. (or just height if you want to try the stock needle). The thickness affects 1/8 - 1/4 throttle. On my 1994, a one step thicker needle cleaned up that area, per Jeff Fredette's suggestion on an FMF pipe.

[Broken Wrist]

Thanks again KDXGarage!!

I like wrenching but I wasn't sure I was chasing the right thing. I will drop down a couple pilot sizes tomorrow and see what happens. If I can get the idle and air screw to have some affect I will follow the jetting guide and move onto the needle and main. It is definitely not riding weather here but this is a new bike to me and I would like to get it running clean. I also understand jetting will change with the weather. I will get back with results because it just might help someone else that's crazy enough to live in this heat. Thanks !!!

[KDXGarage]

No problem. Definitely start at the pilot and work your way up the throttle range. All circuits are in play at 3/4 to full throttle, so getting the lowest ones first is the way to go.

[Broken Wrist]

I finally had a chance to play in the garage today, I dropped the pilot Jet to 42, then to 40. The idle screw is now working about as it should, but the air screw still has very little effect on RPM's. I can stall the motor with the air screw all the way in, but that's about it.

Throttle response is crisp, quite a bit of white smoke when coming off the pipe.
The last thing I did was change the main jet down to a 152 (I couldn't help myself I had to see what that would do).

Temperature 114 degrees
Elevation 500
Humidity near zero
FMF Desert/Airbox lid removed
Fresh top end

I will try the 38 pilot tomorrow, Any other suggestions??
Thanks

[TasKdx200]

no suggestions but have a very very similar situation. I’m using JD jetting red needle at the 4th clip, 145m and 45pilot, 1150 elevation, mid 70’s, dew point around 55-60. getting a little idle adjustability with idle screw, not so much with air screw.

I checked the idle screw when the carb was out and it does affect the slide when I turn in/out the screw.

[Broken Wrist]

I did the same, then I tried leaving the idle screw turned way out and kept the bike at slightly high idle using the throttle, still nothing much going on with the air screw being turned in and out. I don't get it.

[Broken Wrist]

Its pretty hard to get a bike jetted correctly when the air screw doesn't do anything.

[John_S]

I would try another size down on the pilot like you're going to do. It's really important to have it at full operating temperature. You want the cylinder to be "cleared out" and fully hot. If you're starting it in the garage or driveway and then messing with the air screw, it'll get frustrating because it just won't react the same way as when you've ripped on it for a few minutes. It could have excess fuel in the cylinder and pipe if it's been rich and sitting there idling.

[Broken Wrist]

Thanks for your input John_S,

I have been giving the bike a couple good rips on the throttle to clear it out while sitting on the stand in the garage, but what you said makes sense. I'll be back at it tomorrow and run the bike through the gears before playing with the air screw and see what happens.

Thanks again !!

[jamiethegiraffe]

I’m also running a 38pj in an RB’d 220. My idle screw works but I find that the air screw doesn’t do much to change the rpm- unless I turn it too far in. Then it’ll stumble and die.
That said, I adjust my air screw for best throttle response. I have a JD quick adjust air screw that makes it easy to tweak- even while riding.

[Broken Wrist]

Interesting, if I can't get the air screw to change the RPM's with a 38 pilot I might try that. That is exactly what I'm getting is stumble and die with the screw turned almost all the way in.

Thanks for the info !!

[Alex.01.220r]

Hey man, following your post because I have a 01 220r and the same issue. Buddy of mine is helping to figure it out. Currently pilot is at 38 and going to do a mid body gasket kit next. If nothing were going to do a Leak Down test.

[Broken Wrist]

Okay Cool,

Maybe you can add to the post what you find.

I still haven't done a leak down test, I don't have the stuff for that yet. I did replace the jet block gasket if that's the one you're looking to change next. Mine looked fine and didn't solve my issue.

I did spend the day in the garage and started by going down to a 38 pilot, there was really no noticeable change between that and the 40 pilot.

I started to re-think things and went back to stock everything. I went back to the OEM needle R1174K, 48 pilot and 160 main. I had replaced the stock needle with the one that came in the rebuild kit.

I worked my way back down on the pilot jet blowing the bike out before attempting to adjusting the carb. I started to see a noticeable difference to the air screw back at the 40 pilot. The air screw would now change the RPM's (not super noticeable, but there was a slight difference) and the Idle screw started working pretty good as well.

I was still seeing a fair amount of white smoke when blipping the throttle so I dropped the needle down by going up to the second clip and I dropped to a 152 main (I don't really know why it just felt right - haha).

I took another quick rip up the street and it seems to be much better (not perfect but better).

I think the aftermarket needle may have been causing my issue, and maybe the smaller main jet also helped out, but I really don't know if those would have had anything to do with the air and Idle screw at low RPM.

Anyways, it was a 115 degrees here today and test riding a bike is brutal. I am feeling better about things and I will be working to dial in the needle next.

Thanks to the people here that took the time to give me advice, I used it all and I'm not done yet !!

[KDXGarage]

Dude, no pun intended, but where the HELL do you live? What is the "feels like" temperature?!

I am glad the bike is running better. YOU MUST change the jets when cold weather comes around or you will be running real lean. Well, not you, bu the bike. :-)

[Broken Wrist]

That's funny, I live in Lake Havasu City, AZ. It's all about boating and water skiing this time of year. If your not playing in the water you're looking for shade and A/C.

It's supposed to be 119 degrees today, it's a dry heat so the "feels like" temp probably only 117 or 118.

Thanks

[TasKdx200]

Good info Broken Wrist……my next adjustment is going from a 45pj to a 35 just to try it. I have a 42 but for some reason I didn’t think to try that with the current needle, clip position, and main jet. I’m sure we’re getting very proficient at taking the carb out that for me it’s not a big deal to just try something different to see if there are any changes.

[KDXGarage]

4 sizes smaller is a huge jump