Random, wandering, inconsistent idle on 99 KLX250

[Yamezz]

Hi. We recently bought a 1999 KLX250 for the missus, but we're having problems with the idle. It's basically all over the place - one minute idling so low it's about to stall, then next it's idling at 5,000rpm. It's a Keihin CVK carb, running 138 main, 35 pilot at 2+3/8 turns out. The jets look clean, the diaphragm doesn't appear to have any leaks and we've fitted a new o-ring to the intake manifold. The slide also appears to be returning fine.

Exhaust is standard, but the previous owner pulled the top of the air box off.

Any help would be very much appreciated.? The missus isn't too happy about coming off the throttle and having the bike plough on. I keep telling her it's good for her corner speed, but she doesn't see the funny side of that.

[4strokeridertt]

Check for a vacum leak on the intake. A leak can cause the carb to search around like that.

[Tremor38]

Hi. We recently bought a 1999 KLX250 for the missus, but we're having problems with the idle. It's basically all over the place - one minute idling so low it's about to stall, then next it's idling at 5,000rpm. It's a Keihin CVK carb, running 138 main, 35 pilot at 2+3/8 turns out. The jets look clean, the diaphragm doesn't appear to have any leaks and we've fitted a new o-ring to the intake manifold. The slide also appears to be returning fine.

Exhaust is standard, but the previous owner pulled the top of the air box off.

Any help would be very much appreciated.? The missus isn't too happy about coming off the throttle and having the bike plough on. I keep telling her it's good for her corner speed, but she doesn't see the funny side of that.

Not sure if that year had KCAS, but make sure any vacuun nipples are plugge on the carb end.

Also -if havent already- you might want to pull the fuel screw to check that area and the screw itself. Jus make sure you retrieve the spring and O-ring when you pull it.

[Yamezz]

Just thought I'd bring (belated) closure to this thread. The problem was worn intake valves. Once the valves were done it idled perfectly.

[Blackheart]

Thanks for following up! I would have bet it was a vacuum leak. Didn't know the intake valve clearance would do that to the idle...