Honda NSR 125 jumps up to max rpm in neutral

[pwb]

Hi, my daughter has a NSR 125 2001, Its okey when she drive it, but at neutral or when holding the clutch in the engeine can jump up to 11-12.000 rpm. This also happens when starting it and when the choke is turned off then the enigen very often jumps up tp 11-12.000 rpm. Has to turn it off or put it in gear and realse clutch to have it come down. We have cleaned the carburetor and there isnt any leak in the manifold. The gas wire is ok and the carburetor piston is all the way down. How is it possible to jump up to max rpm when the airflow is close? It dosent do it when there is load on the engine, only when its runnign in neutral or with the clutch in.

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That doesn’t make sense. It has to be getting more fuel and air in somehow for the engine to rev that high. How experienced is your daughter? Could she be leaving the throttle open when sitting stationary?

Is the throttle slide properly spring loaded to keep it down when you roll off the throttle?

My first thing would be to check for an air intake leak from carb to engine. Spraying carb cleaner around the area with the engine running could prove this as the revs will rise when it sucks in the carb cleaner.
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TZR250 2MA road, TZR250 1KT road, TZR250 2MA race, TDR250, YZF-750R Boost colours.
Jaguar S Type 3.0 V6 Sport R, VW Transporter T5 GP LWB Shuttle 140ps DSG.

[pwb]

No, it doesn't make any sense, i have started it and the same thing happens, i have taken of the air filter to see the caburetor piston and its closed. When chock is on it dont rev to max rpm, but if i start it, let the chock on for some time, take off the chock and give it a litle throttle and then reaelse the throttle and the carburetor piston is closed it could go 2-3 sec and it could rev up to 11-12.000 rpm. Sometime its hard to stop with the killswitch when this happen, but the ignition always work, the killswitch allways work, but in 50% of the high rpm trouble it doesn't. I have coated the manifold with some rubber since it is old and have som cracks on it, but it wasnt cracks all the way through, but i sealed it with some liquid rubber just to be sure. But i will try to spray some carburetor cleaner arround it later today to check.

[Hetzer]

Try a new spark plug.
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"There's the horizon! Ride hard, ride fast and cut down all who stand in your way!"

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[Tankie]

initial thought says "air leak"
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Always learning, everyday is a school day

[1198]

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[Hetzer]

[Easy-X]

Given how easy it is to eyeball a spark plug gotta be worth a look!

If I had the time I'd be looking at: throttle, throttle cable & carb. Probably even go as far as stripping the carb down and really giving it a good clean (also might notice anything cream-crackered on carb if lucky.)
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[Pete.]

More info required but it does indeed point to an air leak or split intake rubber. If (as seems to be the suggestion) it's randon and not every time then suspect an air leak between the carb and cylinder.

Could also be a loose jet in the carb.

First, check the carb is not loose on the rubber and then check the rubber is not split. After that, pull the carb and get it fully apart.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[pwb]

Removed airfilter, the carburetor piston is at bottom. Started it up with chock on, took off chock, it runs okey for 1 min, gave it a litle throttle then it goes crazy, jumps up to 12.000 rpm. Ingition off, killswitch off, still running, carburetor piston is at bottom, put my hand in front to chocke the air, didnt feel any vaccume but thats correct since the pistion is at bottom, took 2-3 sec before the egine shut down. My hand was wet with gas after holding it tight in front of the carburetor but thats normal i think?

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As people keep mentioning, it's most likely to be an air leak. Try either spraying a non lit blow torch or carb cleaner around the intake area between carb and cylinder and watch for the revs rising as it draws combustible material in with the air.

Or try the rear tyre or plug just for shits and giggles.
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TZR250 2MA road, TZR250 1KT road, TZR250 2MA race, TDR250, YZF-750R Boost colours.
Jaguar S Type 3.0 V6 Sport R, VW Transporter T5 GP LWB Shuttle 140ps DSG.

[pwb]

Tried to spray startgas all over between carb and cylinder, didnt do anything with the rpm.

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[Nobby the Bastard]

Your throttle is stuck fractionally open. The most likely cause is the cable is over adjusted.
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[Pete.]

[pwb]

This is how the carb looks like when this happens.

[alains]

very often when the cable begins to split it does that
replace the cable (a special with a splitter around the oil pump)
ref : 17910 KBS 900 £28,46 at david silver spares
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