NSR 125 alcast - spluttering 6-7k revs

monty16v · Two Stroke Sniffer Joined: 12 May 2011 Karma :

hey just bought a nsr 125
bought the bike not running and got it running myself
but the bike splutters and backfires around 6000-7000rpm and wont rev any further
any ideas ?
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OffTheClockMotorSport

sandman1976 · Nova Slayer Joined: 08 Apr 2011 Karma :

Backfiring tends to be over fuelling as far as i have learned..
mixture setting on the carb, lean it out and see if it cures.
Pin might be set too high/low in the carb.
Blocked air filter can cause spluttering.
water in the bottom of the fuel tank.
A split somewhere causing it to suck air.
(inlet manifold, gaskets etc)

skatefreak · World Chat Champion Joined: 06 Feb 2010 Karma :

Hey,
do you know if the power valve is operating correctly?
I wouldnt expect it to do that if it wasnt but its right in the power valves rev range and could be a contributing factor....

-Jvr

monty16v · Two Stroke Sniffer Joined: 12 May 2011 Karma :

skatefreak · World Chat Champion Joined: 06 Feb 2010 Karma :

Hey,
funny that, I'm a bike guy who just bought a car thats turning into a project :p haha.
I'm sure you'll be fine though.

PM me if you need a manual for the bike, can be useful at times.

The powervalue is just underneath the tank towards the front right, quiet obvious when you look under the tank, this opens and closes to increase the exhaust port when required.
From 0-2k rpm it should be open and from 2k- 7.5k should be closed, beond that it should stay open. This helps get the most linear power curve out of the engine.

When you go to the bike and start up, rev up a little past 2k and see if the servo moves. If its not moving on the bottom end then it wont be working on the top end.
It seems people think its cool to cut the cables to the servo and pin the servo closed, it gives the bike a much more punchier delivery but does no favours through mid range.

It also sounds like you could be running a little rich on the oil, if you take the service pannel off the right, front mid pannel, you will then get some access to the engine.

Looking for a suitable image I came across a little tutorial on this which covers it quiet nicely (the 150 and 125 are the same).

So, R/C valve okay, oil pump checked out due to your thoughts on the plug...
I'm not to sure what else it could be but will have a think. Maybe compression test, clean the carbs and check the air filter whilst your going over the oil pump?

Best regards

-Jvr

Ps, with this in mind i have found my NSR a little hesitant to pull through the power band for the first time each ride lately. Warmed up as usual etc. Will give her a good servicing, carb, clutch (been putting off for a while) stator, reg, battery (I will nail that leccy spook!) de-coke head and exhaust, reeds, clean air filter, sparkie, front disk, pads, brake fluid (maybe caliper seals), fork seals and fluid... I have most of the parts here anywho lol.

dangerousdave · Traffic Copper Joined: 22 Apr 2011 Karma :

Does sound like the engine is running too rich.

Is the air filer clean ? This can cause the spark plug to foul up.

Would be a little cautious about leaning off the oil pump straight away, the oil keeps the engine alive ! I've found these don't usually require any adjustment.
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1988 Kawasaki KMX 200

Previous: Yamaha YZF1000, ZZR600, KMX200, DT50, KX80, CG125, PF50

Truzo · Nova Slayer Joined: 03 Sep 2010 Karma :

I have had this before. Could be too much fuel or too much air.

Check your carb settings. Make shure all your jets are clean and air filter + foam is good.

If its still playing up then you probably have a air leak some where.

Also. Check you have the right plug in it.

Truzo
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Current Bikes: RXS 100, RD 125lc3, RD 350 F2

skatefreak · World Chat Champion Joined: 06 Feb 2010 Karma :

I'm not suggesting leaning out the oil pump but checking to be sure its correctly ajusted...

-Jvr

monty16v · Two Stroke Sniffer Joined: 12 May 2011 Karma :

was speaking to a couple people today told me it could just be the carb needs cleaned. gona try that tomorrow see if it helps any
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OffTheClockMotorSport

monty16v · Two Stroke Sniffer Joined: 12 May 2011 Karma :

took off carb today and cleaned it, blew out jets and cleaned tank and fuel lines. bike going bit better but i noticed the intake rubber from carb to the engine was perished could this be the cause of the problem?
no airbox in the bike either i noticed when stripped it down ordered one today
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OffTheClockMotorSport

dangerousdave · Traffic Copper Joined: 22 Apr 2011 Karma :

if its running without an airfilter/box this will affect the ratio of fuel and air which is going into the engine.

Let us know how you get on when the air filter is fitted.
____________________
1988 Kawasaki KMX 200

Previous: Yamaha YZF1000, ZZR600, KMX200, DT50, KX80, CG125, PF50

monty16v · Two Stroke Sniffer Joined: 12 May 2011 Karma :

well changed the inlet rubber and got an airbox and fitted it, tried new copper plug, new iridium plug
still no joy
looks like im gona have to take it to a mechanic
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OffTheClockMotorSport

leepick · Scooby Slapper Joined: 24 Jun 2011 Karma :

if its doing it around 6k-7k its probly your cdi unit is restricted. u can derestrict them your self easy
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Aprilia RS125

monty16v · Two Stroke Sniffer Joined: 12 May 2011 Karma :

bike is japanese import, and its 1991 i dont think they were restricted, and sometimes it will rev out past 7k but then just starts same problem

gona have a look at the powervalve tomorro and if thats not whats wrong im gona have to take it to a mechanic
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OffTheClockMotorSport

monty16v · Two Stroke Sniffer Joined: 12 May 2011 Karma :

a years MOT on the wee bike today

still going absolutely terrible

was speaking to a friend on way home that knows about bikes
he listened to it and said it might be a broken ring?
i asked him about the powervalve sticking shut he said it wouldnt make it backfire the way it is doing

would a video of what the bike is doing help anybody on here work it out?
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OffTheClockMotorSport

monty16v · Two Stroke Sniffer Joined: 12 May 2011 Karma :

took the cover off the powervalve today

it doesnt seem to be operating correctly

it closes ok over 2k rpm and opens ok under 2k rpm
but it seems hesitant to open again at 7k
then sometimes it is not operating at all, staying in the closed position

when i start the bike and kill it with the key it stays in fully open position.
how do i disconnect the servo and where is it ?
so i can take bike a run see if it revs better with rc valve in open position

cheers monty
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OffTheClockMotorSport

Stowelly · Traffic Copper Joined: 25 Oct 2009 Karma :

monty16v · Two Stroke Sniffer Joined: 12 May 2011 Karma :

i dont think its restricted because sometimes the powervalve will move and the bike will rev

does anybody know where the powervalve servo is on a jc20 model
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OffTheClockMotorSport

monty16v · Two Stroke Sniffer Joined: 12 May 2011 Karma :

followed the cables from the valve itself to find the servo under the tank.
so stripped that off and found it was actually a loose wire
i think it was green there was 2 spade connectors one was off, over to the left of the servo

once i put the wire on the bike went a lot better so i stupidly put it back together and now it has come loose again lol
will have to secure it a bit better this time
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OffTheClockMotorSport

monty16v · Two Stroke Sniffer Joined: 12 May 2011 Karma :

have the wee bike running 100% now but the clutch is slipping a little at high rpm. can they be adjusted or is it new clutch time. and if so what would be the best make of clutch to buy? and should i upgrade the clutch springs while im at it
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OffTheClockMotorSport

skatefreak · World Chat Champion Joined: 06 Feb 2010 Karma :

Ajust the clutch cable at the engine end to try over come this.
I have has simular problems myself but these clutches do last a while, can get fiddled about with and need re-ajusting at times.

Best regards

-Jvr