NSR125R stalling.

[Darylw27]

I've had an issue with my NSR for a while now. When pulling away my bike will stall unless the choke is always on. With the choke off I have to rev it well over 7k to stand any chance of pulling away without it stalling. Basically if it hit under 4k revs without the clutch it will just die.

I've noticed that the powervalve/servo? Is broken and won't open or close and is stuck on High. Any chance this is the problem for lack of low end power? and why would leaving the choke on help it? Bike also has issues starting even after been warmed up.

So far cleaned the carb and changed the spark plug. Neither made any improvement.

[P.addy]

My RS power valve was jammed open purposefully.

I had to rev to 4k minimum to pull away anyway... Thought it was a 2 stroke thing.

You dont start it warm with the choke do you..?

[Livefast123]

My NSR would pull away easily with about 4k and i'm not the smallest chap in the world It's all about feeding in the clutch on small 2 strokes.

If it runs OK with the choke on that would tell me that she is running lean. You need to start checking for any air leaks on the intake side. I would give the carb another clean with carb cleaner and compressed air just to make sure you did it properly.

Also having the powervalve stuck open isn't going to help matters but it shouldn't cause the dodgy pull off. If your starting it off the choke constantly then you will knacker the plug very quickly which would cause lots of issues.
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Current ride - Yamaha MT-07

[alains]

this is a wellknown bug
it appears when the choke cable is jammed by dirt or when it has sharp bend , the piston does not close the bottom hole .
after checking the cable if bug is still on go to https://www.dellorto.co.uk and order these spares
carb 28PHBH/FS or /FD
1 spring #3133
1 piston #3138
or repair kit #53003
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the worst day fishing is better than the best day working

[Darylw27]

@Paddy - It won't start without the choke even when it is warm, attempting it without choke even when warm it will just tick over.

@Livefast - I'm fairly average if not on the smaller side and there's no chance it will do it without the choke. When filtering slowly too I need to ride the clutch unless i'm going faster than 10mph or I risk stalling.

My mechanical knowledge is pretty limited though I am trying to learn and take it all in. Already had a friend who's a mecanic check to make sure it wasn't lean or rich. But I have noticed that the plug is fouled and pretty black/oily.

@Alains - I'll check the choke cable and get back to you.

Big thanks to everyone, all the help is much appreciated.

[P.addy]

Black plug means its being fouled... mainly as you run on choke.

Have you tried upping the idle speed when its warm...

[Darylw27]

Yeah I've played around with the idle for quite a bit from the recommended 1.4k up to ridiculous amounts like 3k all the same issue.

Reminded me of another problem relating to this being that without having the throttle open slightly at lights etc it just slowly dies dropping about 100 revs every second until it stalls.

[P.addy]

Can I suggest getting your choke cable looked at and a new spark plug... a fouled plug really wont be helping you at all.

Check the carb and airbox are seated correctly when you check the choke cable.

[alains]

bla ! bla ! bla !!!!!!
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the worst day fishing is better than the best day working

[Darylw27]

Ok finally had some time off to try a few things and on friday I'll give it the full whack. Put in a new spark plug, checked choke cable and it seemed to be ok though some pictures if possible to know what is and is not correct would help as I don't know 100% what is and is not normal. Just checked airbox and cleaned the filter etc.

As for checking for airleaks would I be right in saying that can be done with the engine running and spraying around the intake with WD40/Carb cleaner? That's what a friend of mine told me to do.

To make sure I'm cleaning the carb correctly could someone give me a step by step guide or if possible pictures would be most helpful. I do have a vague idea of what to do, just want to make sure it's done right as i'm still very inexperienced.

Many Thanks.

[st3v3]

[bouncerdove]

Hi. Have had a simular problem with my sons jc20 and got some good advice from this forum. The problem with his bike was two fold..
1 the RV cables from the servo to the RV valve were reversed at both ends, The cable with the spring compressed rather than open the valve.
2 The crankshaft seal on the clutch side was leaking oil into the crank. This gave the impression when looking at the plug it was running rich (fouled up sooty), when in fact it was running weak due to lack of fuel coming through the carb.
When these two problems were fixed the bikes power increased greatly and could pull away at 3.5k easily (instead of about 6k).
Hope this helps
Regards bouncerdove

[st3v3]

If the OP's NSR is foxeye, (JC22) then it's a different engine to the JC20.
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Roger wrote: Women don't get damp for clingy puppies. Get some better happy pills, hit the gym & buy a medallion the size of a dinner plate. Job done

[alains]

wrong sir !
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the worst day fishing is better than the best day working

[bouncerdove]

Alains is correct. JC20 & JC22 are the same engine with a few changes. Port size, ignition timing, and on some the carb size. the rest is ancillary changes.
regards bouncerdove

[st3v3]

Alains, at least explain why someone is wrong so they can correct themselves

I thought the JC20 was the italian alcast NSR? my mate got one of these and took a foxeye (JC22) engine to put in the Alcast but it wouldn't go, they were different?
____________________
Roger wrote: Women don't get damp for clingy puppies. Get some better happy pills, hit the gym & buy a medallion the size of a dinner plate. Job done