Nsr 125 Backfiring at certain Rpm's

[mysterydudes]

Hi there,
i recently bought a 2000 nsr 125 r and ran perfectly untill a few days ago. It started to backfire at around 8000rpm jerking backwards and forwards in all gears including neutral (except jerking), it used to fly past it no problem. Now it is doing the same at around 5000rpm as well. I changed the spark plug, cleaned the filter, adjusted the carburetor mixture but it didnt change the situation. Does anyone know anything i can do, ive seen other posts like this but they seem to be different and this one seems to be getting worse and worse.
Cheers....
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L.James

[temeluchus]

Try setting the mixture screw back to factory setting, then drain your float bowl. Possibly water in your carby.
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Some shite cruiser. Now with guns and FREEDOM!

[mysterydudes]

cheers..... ive done them, it seems going past 5000rpm is better now but the 8000rpm problem still exists. Any other suggestions?
thanks
____________________
L.James

[skatefreak]

8000rpm is roughly when the powervalve should reach fully open, check it in neutral to see if the servo (under the tank to the right) is moving fully (check back of the cilinder that turns, theres a grove to show full travel).

Long shot but it might have something to do with it.

Is there plenty of smoke when starting from cold?
Engine temp usual?
Maybe give the carb a clean...

Compression test maybehaps, check the condition of the top end...

-Jvr

[temeluchus]

[mysterydudes]

I riden to work today and the problem does still exist, it seems when the bike properly warms up it become worse. its becoming unridable as i have to try and keep my revs between 1000-5000 + 6000-8000rpm. I've spotted nothing unusual since i've had it and everything seems fine I'm gona have a tinker with it and see what i can do but i think i might have to book it into a garage... money money money.
Thanks for the advice, have any other ideas?
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L.James

[temeluchus]

little point until youve had the carb off.

Worse when warm usually indicates richness. Possibly could be knackered float valve.
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Some shite cruiser. Now with guns and FREEDOM!

[alains]

warm your bike for 5mn then lift your tank on it's stand
start again , watch the pulley on the right and see what it's doing when you accelerate as :
- contact (initialization) LO
- start and idling under 2000 HI
- 2000-7500 LO
- over 7500 HI
tell me the result , does the pulley moves ?
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the worst day fishing is better than the best day working

[mysterydudes]

Thanks for the replies, but i took it to a trusted garage and he said its basically scrap..... theres about 500-1000 worth of damage to the engine and other parts. So guess i'm looking for another bike then.
Thanks
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L.James

[alains]

why doing so ! just slightly stupid
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the worst day fishing is better than the best day working

[skatefreak]

Engine off flea bay - £275-£300...
Really think it would be financially viable to get hands on with this one.

If not,
you selling the bike?
Would be interested in coming up to have a gander.

-Jvr