nsr 125 rc valve

[richieu10]

Hi i have a 2003 nsr 125. it runs ok up to about 6000 rpm then starts to backfire when the engine is under load, its had new air filter spark plug and carbs have been cleaned it looks me like the rc pump isnt adjusted correctly as it does move freely, anyone got any ideas, as i fiddled with the adjustments slightly on the pump and now it wont start at all

thanks

rich

[skatefreak]

Are you refering to the [img=https://2.bp.blogspot.com/-I8DZyts2GN4/UaHgsJCOmUI/AAAAAAAAGzg/F1i6vhmzKnE/s1600/TheTRXproject_Honda_NSR_125_JC20_RC_Valve_photo_01.jpg]power valve?[/img]

You say it moves freely, which it shouldn't as there is a [img=https://i.ytimg.com/vi/BlelJrdLt9A/maxresdefault.jpg] servo (that spins a the silver wheel)[/img] that holds it open/closes it, maintaining tension on the cables.

The valve should be open around 0-2000rpm, closed from 2,000 - 7,000 rpm and open again > 7,000. This valve ajusts the exhaust port timing allowing decent mid range and good top end (well, once de-restricted ).

Turn on the ignition and the servo should automatically move to the open position. If it is not doing this then you have a problem. If you don't have a servo in the tray ie nothing connected to the cables or even no cables, then you have a problem (O_o).

You can 'pin' the valve open, some believe it gives more 'top end' but renders your mid range barely usable (gutless) and your throttle is no longer linear so after giving it 2/3 throttle to pull away you'll have to whack the throttle back as it comes into the power band and launch commences (takes a bit of getting used to...).

Unless its the oil pump you've played with... that wants to be set to factory and left alone


As you say you've diddled it and it will no longer start, you may have moved the valve to the closed position which will not help idle or start up I suspect. Moving the power valve to the opposite position its in now and see if it helps get her started.

Ps. I have a spare power valve, someone was asking for one last week

[-]

My UK model had a loopback jumper fitted in the wiring box under the tank. With this fitted it retarded or disabled the PV, can't remember which now.

Unless the PV has flipped completely, it should still run over 6K without backfiring, even if closed and not operating. It was an easy way of restricting some of them.
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Jaguar S Type 3.0 V6 Sport R, VW Transporter T5 GP LWB Shuttle 140ps DSG.

[alains]

your bike is probably a swiss import (VIN begins by ZDCJC22E........)
if it's the case you may have a red shunt (see pict)
they have been shunted to limit the speed at 50 MPH
just take off the top (connector #3) and you will recover your full power
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the worst day fishing is better than the best day working

[-]

That's similar to the jumper my UK bike had. It didn't restrict it to 50mph, but stopped the RC valve fully opening.

With it fitted, it had plenty of bottom end grunt for a 2T 125, but you could feel it being held back at higher revs. Still did around 75-80mph indicated though.

Got a feeling my jumper was a white and either red or green stripe wire.
____________________
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.