I am having a problem with my idle and I am out of ideas. The set up, full KLX 300 exhaust with end cap on (running a 300cc kit). DJ kit per instructions, needle on 4th clip, 128 main, stock pilot, 2.5 turns out. All free mods done, include smog block off and crankcase vent. No airbox lid and a K&N filter.

The problem is that the idle will hang at about 2000 RPM and then, after about 20 to 40 seconds will settle to 1300 or so RPM.

I have tried a ton of things, including trying the stock needle (even though I know the needle has nothing to do with idle) taking out the slide and putting it in the freezer to ensure the boot didn't expand, checking the boot for holes, replacing the carb vac block off nipple, giving the throttle more slack and I even removed the Kabuta adjustable mixture screw and put the stock one on. Further, adjusting the mixture screw in or out does not solve this problem either. Finally I sprayed WD40 all around the carb boots and vac port to see if I had an air lead, nothing noticed.

I am not sure what is causing it, any ideas? My last thought is that maybe it is a float height issue, I have jetted the carb a few times and could have hit the floats out of adjustment, but I am not really sure this would cause a hanging idle like this.

 

Does adjusting the mixture screw in or out change the idle? If not, the carb isn't operating on the pilot circuit.

Ride on
Brewster

 

When your idle hangs then drops, you're lean. When your idle drops then raises back up, then you're rich. Try changing your pilot jet to 38. I had that experience before.

 

The mixture screw setting will make the bike idle worse, but it doesn't fix the problem. I do agree it seems like a lean issue and I have a number 40 pilot, but really, I shouldn't need a larger pilot with this set up.

 

I had a very similar problem.
Revs were hanging high.
They would drop down by them selves after 10-30 seconds or I could force them down by letting the clutch out whilst it was in gear.
I suspected it was a small air leak on the inlet manifold side of the carby.
I pulled the carb, removed the bowl and slide and gave it a good squirt with carby cleaner.
In all the holes and jets.
Cleaned the rubber boots and carefully put the carb back on, making sure that there was no leaks and no dirt anywhere.

I also checked all the cables etc as I had the carb out.

Put it back together.
Fixed.

I don't know exactly what was causing the problem but heh, whist you have it apart, might as well check everything right?

But, I have a pumper and not the stock CV.
I would still be suspecting an air leak though.
Possibly a sticking carb slide?

 

Yeah, it sure does sound like an air leak, I suppose I can take it all apart again, I mean, by now I can have the bike apart and carb out in less than 30 min...

 

Yeah its a pain in the rear end.
And there is nothing worse than putting it back together and its still not right.

Good luck man, I hope you sort it out.

 

Yeah...your set up shouldn't require a bigger pilot jet so I'm thinking air leak might be the problem.

 

Just a thought, check the vent lines. If one of the vent lines was obstructed could it affect the slide?

 

I did check the vent lines, but it is worth checking again...thanks! But here is a stupid question for you all, the slide boot, when you replace it, is it inverted like an "inny" belly button, our up, like an outy? (technical carb talk eh?)