KX100 Idle help

[griffbones]

Has anyone else had problems maintaining a decent idle on their KX100?
I have been working on two strokes for about 25 years now and I am stumped.
I just put a new 2007 KX100 engine, carb, pipe and all electrics in my sons 2005 KX85. The thing runs like a champ except I can not get it to maintain a good consistant idle. Once in a while it will idle pretty decent but if you go run the bike through the gears and then come to a stop it hardly wants to idle again. The engine is not slow to return to idle, it has a nice tan plug, and good throttle response even from this low idle.
I even swapped out the carb for one of my other identicle carbs from our KX85 (I had to change to the KX100's needle and 138 main jet though) but it still acts the very same, absolutley no change. I have sprayed carb cleaner and brake cleaner all around the base of the cylinder, around the reed cage/intake boot and around the carb joint and don't seem to pick up a vacuum leak. Also tried spraying behind the ignition rotor while the engine was running to try and see if the crank seal was leaking, but again I picked up no vacuum leak.
Turning in the idle speed screw will not help either; it will raise the idle for about two seconds and then it falls back down to a very low idle again. Adjusting the air screw helps very little as well. Is it possible I need to go up to a 48 pilot jet from the stock 45? Normally I find these bikes are already jetted rich, but this thing almost acts better when the air screw is turned in further (like only 1/2 - 3/4 turns out) yet this dosen't really solve the problem either. This same carb worked and idled perfectly on our KX85 and the only changes have been to install the NAPF needle and the 138 main jet per Kawasaki specs for the KX100. And as I stated the new carb that came with the engine runs exactly the same, so I know it is not a defect in a carb. BTW every thing is currently set to stock jetting specs and I have tried the stock air screw setting of 1 3/8 turns out as well as everything from 1/2 turns out to as much as 3 turns out ( I know beyond where it should be set).

Any Ideas guys? Sorry for such a long post.

[griffbones]

I know this was a long post to read, but does anyone have any ideas?
Ignition, jetting, air leak that I am not finding?
Has anyone else had trouble getting a newer KX100 to idle well and consistantly?

[motodemon172]

pro circuit specs a 42 pilot jet and changing the needle clip position fron 4th to second (2003 to 2006)which would lean up the slow circuit causing a higher idle.an air leak would cause higher or erratic idling.it could be an ignition problem (stator or cdi) but i would try the pilot jet and clip position first for sure.http://www.procircuit.com/PCJETTING.htm

[griffbones]

Ok it is fixed!
I saw that Pro circuit sheet before, but I still felt that this thing acted lean at idle. So I installed a 48 slow jet, set the air screw to 1 1/2 turns out and it idles like a champ! I also leaned out the needle one clip position as it always sounded rich at just above 1/8 throttle opening, this solved this problem. So until warm weather gets here I think my sons bike is in a good state of tune.
BTW the plug looks great after idling, an easy ride or after a wide open pass; every check revealed a nice saddle tan plug.

[adam_c_]

my kx80 was doing this last week and i found that if you tighten up the throtttle cable it changes the response and turns the idle up, mine was far too loose and idling low and after i tightened it up it was a bit too high then i loosened it a little and it was perfect

[griffbones]

Adjusting the throttle cable is the wrong way to raise the idle my young friend. There should always be some free play adjusted in the throttle cable. Instead you should use the idle speed screw to raise the idle speed. My case was different in the fact that I had a slow jet that was too lean for my current temperatures (30 degrees, low humidity).