6k rev limit
 

Hey everyone, a while back I bought a 125cc chinese adv scooter and it ran fine until recently. The problem I have is that the bike wont pass 6-6.5k rpm amd the power is not the same as it was. It has almost 2k km and I changed the oil on the right time. Does anyone have any ideas on what might cause this?

Something could have failed in the transmission. A broken V-slide, clutch malfunction and broken roller come to mind. A transmission issue can hold the motor back from making full power.

Did you check the valves? Rule that out as its a easy thing to check.

There was something else I was going to mention but my mind is drawing a blank. I'll post up anything else I can think of.

Other possibilities:
Faulty CDI.
Faulty stator.
Faulty coil.
All 3 of the above can be easily tested. YouTube is your friend. I honestly don't suspect any of the above though,BUT rule it out.

How does the spark plug look? Is it lean white/ashy looking or black/rich looking? Should be mocha colored.

Plug the end of the exhaust with a wet rag while it's at idle and see if it stalls. If it continues to run you have an exhaust leak. If leaking the reduction in back pressure can cause weird running (and run the exhaust valves hot because the heat isn't being removed properly).