NSR125F engine problem.

[deputy]

Have recently purchased a slightly shabby 1989 NSR125F. I had a problem early on where it would not rev beyond 5-6K revs. After much investigation, discovered that the previous owner had managed to get the cables on the RC valve reversed. Swapped these over, thought that would cure everything, alas I was wrong, the bike will rev smoothly(ish) to 6k then begins to splutter (misfire?), adjusting the throttle a bit or dropping down a cog will get through this, then the bike takes off. To me it feels like some sort of ignition problem rather than fuel, can anyone help?

[mr jamez]

I would change the spark plug first and go from their.

[deputy]

Have already changed the spark plug, made no difference.

[KevTM]

i have practically the same bike and i posted a thread a few weeks back regarding my bike hesitating around the 4.5k - 6k range. It isn't a problem, jsut a mere characteristic.

They wasy i get round it is to 'gun' it from first and it's ok. If you're gradually accelerating it will hesitate, in which case i either just let it slower progress or i slip the clutch a bit and keep the revs just past 6k.

You might have another problem but just though i'd let you know.

[deputy]

This isn't just a hesitation, the bike struggles to get beyond 6K unless you short shift through the gears then drop it down a cog. This is very inconvenient if you are trying to make a quick getaway.

[McJamweasel]

Try cleaning out the carb.
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BCF: Be yourself, just don't be an arse.

[deputy]

This isn't just a hesitation, the bike struggles to get beyond 6K unless you short shift through the gears then drop it down a cog. This is very inconvenient if you are trying to make a quick getaway.

[deputy]

Have already stripped and cleaned the carb and the air filter. Anymore suggestions?

[dandit]

could be dodgy coil or ht lead could be shit fuel could be restricted could need a rebore the list is endless
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WHAT DO YOU MEAN 100 MPH THATS IMPOSSIBLE I STILL HAD 3 GEARS TO GO OFFICER. Currently riding a naked cbr 600 and driving a 52 plate 2litre tdci mondeo

[deputy]

I don't think the bike is restricted as once you get through 6k rpm it will rev freely to 10k. I have had fuel from several different garages and that makes no difference.

I will try and get hold of a new coil and try that. Does the coil come with the HT lead connected, as my HT lead does not want to come off the coil?

Excuse my ignorance in this matter but what exactly does the RC valve do?

[mr jamez]

RC valve is the power valve, just two valves in the exhaust port controlled by a servo, at low revs it is closed to give you some low down power. At 6-7k rpm it fully opens.

[Ian (GPX)]

Changed the air filter ?

[deputy]

The air filter was cleaned in solvent and re-oiled.

What would be the effect if the RC valve was not shutting properly?

[dandit]

[ts50x0]

hi,
ive recently had this problem on my 1990 nsr and i took it to my local dealer. they changed the CDI unit and replaced the power valve. this made it better but it was also restricted in the exhaust. do you know if the exhaust is standard?? might be woth checking to see if it has a restrictor in it.
hope this helps
sam

[deputy]

The exhaust is original, but I'm fairly sure the bike is an import (speedo reads in KPH). Don't know whether this makes any difference.
If the exhaust is restricted, what would I be looking for and where?

[mr jamez]

Their is a derestriction guide on www.nsr125.com. However yours is an early NSR and should not be restricted. As the previous owner managed to get the power valve cables mixed up, they may also have adjusted it incorectly. The cables have to be adjusted so that the valve opens at the correct moment, PM your email adress and I can send the two pages about setting it from the manual I have

[deputy]

In response to an earlier thread about letting people know the outcome of problems, I would like to say that the NSR is now running like a dream. I eventually traced the problem to the lack of a return spring on the choke, hence the bike has been running on choke since I bought it.
Have put a spring in and in now goes like stink.
Shame that I did not discover this earlier, before I changed the CDI, RC valve servo and controller, ignition coil and stripped various parts of the bike.

Oh well, alls well that ends well. Lets just hope I don't wrap it round a tree now!

[alains]

after a good look of what you said all , it seems to me that's either a faulty RC valves control box or CDI unit . look i what doc i've already put on (jointed here) . prior of that , make this test :
take down your right fairing , open the box where the cables arrive on the engine (where it's a cable with a spring) . start engine choke on , let it warm and take off choke . progressivly take up revs , watch the result on the pulley . now around 7800 revs you must see the indications . adjust it as shown on the RCvalces pictures
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the worst day fishing is better than the best day working

[alains]

i just forgot to tell you that H means High and it must be on High at 7800 revs . if you cannot adjust , it's may be that your valves are stocked by carbon .
hope it will help
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the worst day fishing is better than the best day working