NSR 125 JC20 won't rev past 6-7K 95% of the time

[NSRB]

Hello,

I'm new here but this forum seems to have wealth of knowledge when it comes to NSR 125's. I'm hoping someone will have an idea whats wrong with the jc20 I bought recently. It is a hungarian import.

I dropped it over in the van after a ratchet let go driving it home and it has not run correctly since.

So I purchased a new throttle cable, new plug, new air filter, rebuilt and cleaned carb, played with fuelling slightly as it appeared to be running very rich, cleaned tank filter, new fuel filter, checked rc valve mark, checked oil pump mark, rc valve servo appears to work as it should going from idle to early revs but does not switch back over at 6 / 7k rpm.

No matter what it does not seem to be able to rev past 6 - 7k in neutral let alone under load. It's like it hits a wall and then sputters and coughs non stop and gets very smokey.

Sometimes maybe 1/20 it will eventually break though this rev wall and rev to the redline, but often when this happens the bike starts to "diesel" ie rev under no throttle and when i turn it off this will continue until it burns through the fuel in the carb.

Plug is brown / lightly oiled i've seen much worse so don't think this is the issue.

First 2 stroke i've had and to be honest i'm beginning to think why did I bother.

Thank you in advance for any help if you have any idea what to check next please don't be shy.

B

[Tankie]

First , clean out the exhaust, or at least remove the baffles from the rear of the outlet if they are removable, and clean off ,replacing the glass wadding if needed.
The most important thing with a two stroke is to ensure it breathes correctly.
If this is successful the plug colour will probably change to a lighter shade of brown and an improvement of performance.
The running on is normally caused by carbon build up in the cylinder, if it is not too heavy it will clear on it's own with the increased temp / performance.
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[NSRB]

[alains]

first have your compression tested . if under 120 PSI you need a top-end rebuild . then look your CDI and valves controler . on the short side of the controler you may see TV78 and the CDI may have CI589C or something else . keep me inform of your results , then i may help you
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