My 91 KDX250 won't idle for long, idle screw has no adjustment left?

[Shay]

Hey guys, just bought my first 2-smoke a 91 KDX250 (newby learning fast) and I have a problem my bike will only idle for around 20sec then stall. I have no adjustment left (screw all the way in) on the idle screw. Its a KEIHIN carby i have cleaned. It has the following specs:
Carb Throttle Valve (slider) 5
Jet Needle:R1368H - Circlip right up the top
Slow Jet:40
Main Jet:145
Air Screw:1.45 turns out
New Air Cleaner
New plug:NGK B8EG
Stock exaust and spark arrestor riding conditions are around 30-35degC and 90-95% humidity. Mainly riding on road in slow traffic then weekends forest riding, so its usualy slow going and the no idle thing is :( getting me down.

Any Ideas please, appreciate it muchly ;)

 

[biglou]

I'd say bump the pilot jet up to a 42, and maybe put the circlip in the middle or 2nd form top position.

 

[Shay]

Funny u should mention a 42 biglou the guy i bought the bike from had a 42 pilot jet (the only jet) in all the gear he gave to me with the bike.
So I will give that a try, but can u tell me what the circlip does when u change it from the top end of jet needle to the bottom? Fuel more or less but which end does what?

 

[biglou]

The higher the clip on the needle, the less fuel. And vice-versa. Good luck! :cool:

 

[Shay]

Won't putting a larger pilot Jet make it run (oily) richer? - I have just got the thing to run for more than 1 ride at a time before it used to fowl the plug, I think I have solved it by cleaning all the oil from the air cleaner (it was chockas full of oil and falling apart) I have a new one on order.

Sorry for sounding a little slow but by increasing the pilot jet and and changing c-clip position i should in theory get some adjustment back in my idle screw u think?

 

[darringer]

Not necessarily. Pilot jet only changes partial throttle opening. Richer jetting will give you the adjustment on the air screw to keep it idling. Unless you are idling around for extended periods, it will not make plug fouling any worse. Raising the needle clip 1 or 2 notches will lean out the 1/4 to 3/4 throttle opening to help with the plug fouling.

 

[Shay]

Cheers Darringer, what i'm after is idling at lights in gear with the clutch in on a "two-stroke", so increasing pilot jet size to a 42 and puting the needle c-clip to approx second from top as "biglou" advised, then taking my air screw out more than (text book 1.5 turns) to say 2 turns should give me some idle screw adjustment - yes ?

 

[MrLuckey]

what i'm after is idling at lights in gear with the clutch in on a "two-stroke",

Good luck with that, you may accomplish it but getting a 2-stroke to idle in gear can prove to be tough.

 

[dirt bike dave]

The KDX250's they sent to us here in the states had horribly rich jetting. On my '91, I reduced the pilot to a 38, put in a slide with 1mm more cutaway (a 6), put in the leanest needle listed in the manual (1370, I think). If I remember correctly, my main size was 155 or 158. You can grind away approx 1mm from the bottom of your stock slide if you want to save some money.

This motor can be made to work well with jetting and some minor mods. You can run a thin head gasket from an '88 KX250 for more compression (should run fine on pump premium fuel). The stock pipe weighs a ton and has a pronounced mid range hit. The bike will run better with an FMF pipe, which elminates the hit and adds top end. On mine, when the side KIPS valves were all the way open, the floor of the valve is about 2mm higher than the floor of the exhaust port. By grinding the KIPS valve so that it was smooth with the floor of the exhaust port, the bike picked up quite a few revs and some power on top.

 

[darringer]

You may have to run a slightly higher idle for idling at lights in gear. I know it can be done. My cr will idle just fine in gear for extended periods. It doesn't have to have a very high idle to do this. I like it to idle for hillclimbing and play riding on trails. Another thing to look at is clutch adjustment. Make sure there is no extra play in the cable so the clutch disengages completely with very little drag.