KMX 200 wont idle

Hi all. Ive just got my mitts on a KMX 200 to play with. Its a bit of an odd ball bike in the uk :uk: as the KDX was the popular one. Any way, ive not touched a 2t since i was 17 (now 35) and am after a bit of advice on a tick over issue.

It wont! :cry:

The bike revs well from 1/4 throttle upwards but bogs a little from (held on the throttle) idle. I can get it to idle only by using the throttle, this enables it to tick over at 1100rpm happily but as soon as I shut the throttle it dies. Im thinking the idle jet is knackered/worn/wrong one fitted.

It runs a minkuni 28mm roundslide carb, big one exhaust, stock reeds, and a generic foam air filter. I have cleaned the carb and made sure all air ways are clear, adjusted float heights, jet needle heights, air mixture settings and still no idle despite the idle screw fully wound in. Im about to order a carb kit with new jets etc to see if this cures the problem, but thought id ask the collective minds of TT :worthy: to see if there are other ideas.


If the filter and carb are working fine, then on to the reeds.

Had a nice chat with a local mx garage today. His verdict was "low compression" I forgot to mention the bike is a bitch to start cold which was something he asked as soon as I told him the carb had been strip cleaned. Think I'll order some carb bits for piece of mind (nagging doubt that the idle screw is the right one). The reeds look to be in good condition, no chips, cracks, or other visible damage and they look to "rest" on the block snug. Think ill be tearing down the head tomorrow night and sorting out new piston, rings, etc.

Oh well, I was thinking of taking the head off to inspect and clean the KIPS mechanism anyway, looks like im doing it now, just hope it cures the tick over issue.

compression test??

pressure/vacuum test?

Unfortunately I can't get my hands on a compression tester but I can rotate the kick lever through its entirety by hand with little effort!

Head off (very easy compared to 4 stroke) and piston rings shows signs of passing on the top ring. Light scoring on both piston and barrel, should be able to work the barrel smooth. It doesn't look like the plated stuff I've heard about on these. Wasn't there a steel replacement sleeve you could put in these to get rid of the problems with the plating flaking?

Order a new piston, ring etc tomorrow and build up when parts are in.


Did you get to the bottom of your problem? I am experiencing the same issue with my KMX 125. I have only recently replaced the piston and rings and little end in my bike but last week it broke down and wouldn't start. kept backfireing. Changed CDI unit, checked was sparking (2 month old spark plug), cleaned carb (even tried a different carb), checked kips. It will start ok now (sometimes) but still wont tick over without throttle. I am planning on pulling head off to see if a ring has broke or shattered, only issue is time, I am in middle of exams and its my main form of transport. Also doesn't feel like there is anything wrong with compression and cant get hold of a tester. So please let me know how you have got on. Thanks, Emma.

Hi. Fitted the piston. And ran the engine, still the same. Compression had vastly improved though. Ended up during a carb kit. Going throughv the kit I found a spare o ring. Looked online at microfiche and found it should have been inside the choke mechanism. Fitted this and it ticks over. Happy days. Well not completely. Rode the bike after and was disappointed with the power and handling so sold it on and bought a KTM 200 exc. Very happy days. :)

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