XL 125K2 running issues

Having issues setting up the Xl to run smoooth, so far the float valve has been replaced which made it run better, original air filter has been put back replacing the cone filter and the carb has been full cleaned.

Starts no problem and seems to idle till warm then if rev'd the revs stay around 3k rpm, and will eventually drop but then it can die or start hunting.

Have adjusted the mixture screw trying default settings and then adjusting 1/4 turn in either direction, tried the full in and adjusting till the engine splutters and set back to normal, tried the idle screw, will idle fine till the bike is rev'd then will sit high again. Have moved the C clip on the jet needle, trying all slots and hen checking all adjustments again on mixture and idle but still seem to have the same issues, even checked the points gap and adjusted the plate, still the same. Spark plug does show rich running but all the adjustments don't seem to affect this, so open to any suggestions as to what is causing this now. :thumbsup:

The new alcohol / gas blends kill carbs if left in the carb for a long time.. I found out the hard way.

If the pilot jet has no effect, it could be the wrong jet size or the pilot jet could be plugged up. I gave up on my XR80 and XR100 and just bought new pilot and main jets. About $5 each. The bikes were much better after putting in new jets.

Seems we may have the culprit although until the spares come I can't say for sure, there wasn't much left of the O ring for the mixture screw so could have been letting in too much air, all the jets and other holes have all been checked, cleaned and blown through with compressed air, so lets hope some new O rings witll solve it.

Glad you found the problem. I might need to check the rubber bits on my bikes carbs. The new gas/alcohol blend over here just dissolves rubber parts, such as gaskets and o-rings.

Well I thiught it would fix it, now I'm lost, it will start but won't idle at all, if you let go the throttle it just dies, so seems the o ring had something to do with it, but back to square one with a different issue now, need to know what carb should be fitted to this model before I can go any further, so if anyone can help please let me know what the Carb should be. Thanks

You can Google for the carb model or look it up on a Parts Fische.

ServiceHonda.com is one I use to find parts.

I'm sure TT has them too.

I bought a Chinese aftermarket carb on eBay, but never got a chance to use it. The old carb worked OK after I rebuilt it, then I sold the bike. I think I gave him the carb too.

Check the ignition timing very carefully, I had a similar problem which cured itself after setting the timing accurately. Just a small amount of retard on the timing was enough to let the engine just die at idle.

The problem with setting the points and then moving the backplate to set the timing is that the backplate is a fairly loose fit in the housing so when you move it the points gap changes, as well as changing the timing.

Best way to do it is make sure the backplate is pushed fully over to one side in line with where the points heel is, then set the points. When you then move the backplate, you can push it over it to the same position so you know that the points gap is right as well as the timing.

Takes a bit of messing about to get it spot on but it's worth it.

Good luck,


My sl125 would hang at a high idle when the idle mixture and speed were adjusted to compensate for a worn needle jet. Ran worse when warmed up. Makes it run rich/erratic at low rpm. My plug always looked fine but it just wouldn't idle right and would cough/die with slight throttle. Also make sure the centrifugal advance isn't hanging up. I suppose it could be a vacuum leak. (If it's a small crack it would get worse when warm.)

timing is fine, checked that a few times, have no spoken to a carb specialist and a replacement carb will be ordered next week after pay day

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