NSR125 - Derestriction Help

[mhenry9885]

Hi guys,

I have a problem derestricting my NSR, It won't go above 70Mph and takes a very long time to get there. Here's what i've done so far:

Taken the restrictor plate out from behind the carb (made a huge difference 7500rpm and above)

Checked for a restrictor in the exhaust, nothing there

The bike already had C1626 and TV-78

The jets are 138, 42, 65

I'm presuming the bike was an import as it had a KPH clock.

Any help would be great

Thanks

[alains]

i assume your bike is a french import (if your serial number begin by ZDCJC22B...........) but the previous owner has de-restricted the electronics and upjet . as you are now the bike should reach easily 130 km/h at 9500 rpm . check your max RPM in 4th,5th & 6th gear (not your speed) , then tell me which size in tooth have your sprockets , which kind of plug and reeds
but the biggest improvement will be a race pipe because your's is very difficult (nearly impossible) to de-restrict
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the worst day fishing is better than the best day working

[mhenry9885]

Thanks for the reply, I will check the everything mentioned and let you know. The bike serial number begins with ZDCJC22E, does this mean it isn't a french import?

[alains]

no it's a swiss import . you may have a shunt on the servo . do this test :
- lift your tank on it's stand , on the right you see a pulley with 2 cables . this pulley has a little arrow on it's base and the plastic were is the pulley has 2 marks HI & LO
- put key on , you hear the servo moving ? where is the arrow
- start engine , idle and watch the pulley (must be on HI) where is the arrow
- pass over 2000 and progressively until 8000 , does the pulley move
then report
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the worst day fishing is better than the best day working

[mhenry9885]

Key in - LO (Didn't hear any movement)
Idle - LO
2000 upto 8000 - LO

I will double check it again later just to make sure i have it right.

[alains]

so , your servo is not working . you have a shunt somewhere probably between the white/red (going to the motor) and the green/blue . you must re-establish the normal wiring
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the worst day fishing is better than the best day working

[mhenry9885]

Righty then,

The servo already had the shunt cut out, the red and green wires were modified. I do remember that the servo used to work when I switched the ignition on, I remember hearing it when you turned the key.

After a little fiddling and testing with a voltmeter i found the following (not sure if it makes a difference)

There is 12v going to the TV-78 but only 7v coming back out to the servo. The servo says 12v on the side so I applied 12v directly to the motors inside the servo and they spun perfectly. Does the TV-78 need replacing?

[alains]

the motor of the servo is fed under 12V but the servo potentiometer is fed under 8V (may be it's your last mesurement)
i will explain the colours :
- white & black/white motor feed , applying 12V will move the servo in one way and reversing polarity in the other way
- white/red & green/blue servo potentiometer ends (fed under 8V with a value of 6KOhms +-10%)
- light green servo potentiometer cursor
the 3 other wires are coming from the loom and go to the control unit , they are :
- black +12V from the key switch
- green - 12V from the key switch
- red/white coming from the CDI , it tells the unit at which RPM the engine is (a loose contact at both ends can generate this bug)
download my file https://www.geneva-racing.com/~alains/NSRtips.doc , you will find how works the servo
if you've any question , do not hesitate
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the worst day fishing is better than the best day working

[mhenry9885]

Although the servo isn't moving when I switch the ignition on and go above 2000rpm, when I hit 7500rpm it kicks in and I have loads on acceleration.

Would it be a wiring issue, or to I need a replacement servo?

[alains]

when you put key on the pulley must go on HI and stay there at idle if you are under 2000 rpm , when you accelerate the pulley must go on LO , because closing the valves at this point increase the torque in order to help killing the bike inertia . when your bike begins to fly at 7500 the valves must open to allow more rpm otherwise the engine will splutter (pulley goes to HI)
so something should be wrong with your wiring check it again
https://www.geneva-racing.com/~alains/schema_R.jpg
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the worst day fishing is better than the best day working

[mhenry9885]

The wiring is all ok, there is voltage going right up to the servo so i'm presuming the servo is dead. Whilst i am waiting for another, which position would be the best to leave the servo in, HI or LO, or just not use the bike at all?

Thanks

[alains]

unplug it and with strong pliers catch the pulley and open fully the valves . take this opportunity to check your max RPM in 4th,5th and 6th gear . so when the pulley work will be correct you'll have a comparison
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the worst day fishing is better than the best day working