KX 125 over-revving?

Two-stroke engines can not over-rev. Short of down shifting from 5th to 1st, RPM is limited to the engines ability to scavenge expended gas. If your engine continues to rev beyond where you think it is normal, you old top-end was more worn-out than you thought.

Have you examined your spark plug? It is possible that your main jet is too lean, giving you a lean surge. If this is the case, don't allow this surge to happen, you could seize your engine.

How is your throttle response? It is possible that your pilot jet and needle are to fat, making the main seem lean.

Of course, now that you have replaced all of those worn-out parts, you may not remember what it feels like when the bike gets on the pipe.

i have had simaler problems where by you get too much revs for the amount of throttle that you give it. often this is caused by an air leak into the cylinder, the air bypasses the throttle slide which raises the revs and makes it run lean and bog. if its sitting and you rev it it can take ages for the revs to come down to idle.when you ride it you get the bog and flat spot.
the most common cause of this is a crack or hole in the rubber manifold boot between the carb and the head,either this or the gasket for the reed cage may be leaking.
good luck.

its hard to diagnose stuff from peoples descriptions of their problems... i should have thought of a slipping clutch that really could be your over revving problem. in a bike a slipping clutch ie pretty much the same symptoms as in a car.
ride in a straight line try being in 3rd or 4th gear just at the begining of the powerband and then open it right up.
if its a slipping clutch the revs will start to skyrocket but the bike wont accelerate. in this case check clutch adjustment then clutch assembly (springs,steels,friction plates...) often in old bikes the clutch springs have lost tension and this causes it.
steve.

I have actually owned a 87 kx 125.
If your clutch is messed up i have a whole clutch if u need one perfect working condition....some knotches have started on the basket but still works good

How many other bikes have u owned? I have a feeling nothing is wrong with the bike, i belive that bike has very close gear ratios which if making you feel as if it is revving out to far.

It could be a combonation of the clutch slipping and not very much low end on that bike so it bogs a little then hits powerband and the revs go way up making you think its over revving

There is also a chance you have an air leak

could it be that your silencer packing is all blown out cause the bike to seem very lound making you think its over revving
now that i think of it, doe sthat bike even have a repackable muffler, the one on my bike did not seem rebuildable. there is a chnace that maybe someone just put on a diffrent silencer from another modle vehical (on my bike that is) tho


I just want to say I am not a mechanic, i may be totaly wrong. Those r just a few sugjections because i have owned that model bike.
If you ever need any part for that bike i have all for free if u want them