Overfuelling carb?

[lozza]

Hey guys.

i have an NSR 125 that is definitely cranking and sparking, but refuses to start.

It has had the problem ever since i bought it (after i road it home 20 miles).

i took it to a garage who replaced the plug (and supposedly stripped and cleaned the carb), which got it running instantly, and it lasted me a good 3-4 hours of good performance.

it slowly died again the day after. im certain theres no problem with the electric side, as it sparks.

i briefly got the bike started after removing the plug and cleaning it up, however it died slowly again like it did before.

all the signs point to the carb overfuelling the cylinder and fouling up the plug.

so ive taken the carb out and i just want to know what are some points to check on it that would make it run so rich.

also, the man from the AA who i called out when it broke down reckons that maybe a rubber seal has been broken inside and is causing it to leak. are there even any seals on an nsr carb?

[SillyMe]

This is a needle in the haystack situation.

If it was running fine then died, is there plenty of two stroke oil in the reserve and is the pump working, Smoke from the exhaust will indicate this. Also there should a little drip of burnt two stroke oil that drips from the exhaust from time to time.

Give the carb a good clean, blow out both idle jet and main jet.
Clean the float chamber.
The float sat in the float chamber may be set to low.
You will know it's set to high because petrol will leak from the overflow outlet. There are settings in manuals.
It may need professionally cleaning though?

Two explanations about carb settings on the NSR 125

The idle and mixture screw settings are unique to the bike as it is affected by the temperature, altitude, spark plug condition etc etc.

I do know that is the mixture is set at 1.5 turns out at stock.
So set the mixture screw at that settings and the idle is of course easy to set, around 1500RPM warmed up with the choke off is perfect. After you have got the idle set, you can fiddle with the mixture screw some more and see what works best, only turn it around 1/8 of a turn at a time.


set the pilot screw (the smallest , the more in front) at 2 1/2 turns out
- start engine on choke without acceleration and let it turning until it begins to stuff
- apply a bit of acceleration (2500-3000) , take choke off keep like that for 30s to 1mn
- release right handle and let it warming for an other couple of mn
- adjust the idle screw (the big one with the spring) to idle at 1500 rpm (normal is 1400 but when engine is very hot you'll loose 100 rpm)
that's all
remember : the carb is underjetted (132,38,55) and 2strokes dont like lean mixture . look my file NSRtips.doc , you will see where the jets are and which size is the best.
Source: https://www.bikechatforums.com/viewtopic.php?p=2390678

Electrical issues could be related to pick ups needing cleaning, timing, coil, ignition and regulator rectifier.

https://shop.ebay.co.uk/i.html?_nkw=nsr-125+carburetor&_sacat=0&_dmpt=UK_Motorcycle_Parts&_odkw=nsr-125&_osacat=0&_trksid=p3286.c0.m270.l1313

Regulator rectifier
https://shop.ebay.co.uk/i.html?_nkw=nsr-125+regulator+rectifier&_sacat=0&_dmpt=UK_Motorcycle_Parts&_odkw=nsr-125&_osacat=0&_trksid=p3286.c0.m270.l1313


____________________
Once made equal to man, woman becomes his superior.
The man who says "I may be wrong, but -" does not believe there can be any such possibility
Owned and rode: Honda 100H, Honda MBX 125, Kawasaki AR 125, Suzuki RG 125 Pepsi, Honda NSR125 RK, Honda NRS 125 race bike, Suzuki GSXR 400 Bandit, Aprilia RS 125 O2, Honda CG125, Kawasaki KMX 125, Aprilia RS 125 O6, Suzuki XT225 and now Honda XR 400. ( A few scooters and other dead beats in between)

[Blue_SV650S]

What 2 stroke oil are you using?

How long/far is your average journey?

Do you ever rag it, or just pootling around town?!!?
____________________
The purpose of life is to fight maturity.

[lozza]

thanks for the feedback.

im certain the problem is with overfuelling, it has sufficient oil and the way it dies is not as if the engine was suddenly siezing from lack of lubrication.

it went from running well and idling unnattended, to not idling unless i revved it. then not starting without the choke on.

then very weak and spluttery. then it starts briefly, need lots of revs to keep it running but eventually dies.

after it dies for the last time it wont start again unless the plug is changed.

so i have taken the carb apart, nothing obvious inside it... dont know what size jets are on it... maybe i should just buy a 2nd hand one from ebay.

[SillyMe]

Quote, "after it dies for the last time it wont start again unless the plug is changed".

Just clean the plug with wet and dry paper and leave a 3 mill gap between contacts.

I have to say it does sound like a carb issue.
____________________
Once made equal to man, woman becomes his superior.
The man who says "I may be wrong, but -" does not believe there can be any such possibility
Owned and rode: Honda 100H, Honda MBX 125, Kawasaki AR 125, Suzuki RG 125 Pepsi, Honda NSR125 RK, Honda NRS 125 race bike, Suzuki GSXR 400 Bandit, Aprilia RS 125 O2, Honda CG125, Kawasaki KMX 125, Aprilia RS 125 O6, Suzuki XT225 and now Honda XR 400. ( A few scooters and other dead beats in between)

[N cee thirty]

maybe its down on compression

test that aswell
____________________
'00 Aprilia RS50 > '92 Honda CG > '99 Yamaha Fazer > '91 Yamaha RXS > '79 Suzuki X5 > 01' Honda Cg > 07' Honda Cg > 82' Kawasaki Z200 > suzuki gsxr 400 gk73a > honda vfr 400 NC30 Mod 2 Passed 09/06/2011

Jewlio Iglesias wrote: I actually did vote BNP once

[Blue_SV650S]

Er, my theory was not lack of oil, but the plug 'oiling up' it is showing symptoms of an oiled plug ... it is more likely to oil up if it is cheap oil, not given regular long or 'hard' runs.

It might be fuel level, sure, but just trying to give some alternatives before you concentrate too heavily on the carburettor ....

It might even be the oil pump over-oiling ...

How smoky is it when it is running?
____________________
The purpose of life is to fight maturity.

[lozza]

[Blue_SV650S]

[lozza]

i dont have a camera to take a pic of mine, but this is the same model carb as mine and the screw im talking about is the one circled in red.

there is no screw head on it, but a small stump about 5 mil inside the hole.

the big screw to the left of it is there though...

[Robby]

I would go with a clogged up mixture circuit. To clean this you need to remove the mixture screw, which by the sound of it is broken. Difficult.

[lozza]

[Ariel Badger]

[Blue_SV650S]

[SillyMe]

[Blue_SV650S]

[lozza]

Any pointers on how to check float height, the manual says you need a special tool. Cant see what i can do to measure it... Not sure how to get the float pin out either?

[SillyMe]

Scroll down for instructions. Something about 13mm.
https://www.horizonsunlimited.com/hubb/yamaha-tech/urgent-help-needed-carb-leaking-50217


I would use HOT water, hold upright,pour water into where the petrol goes to see if any overflows through the over flow pipe.
____________________
Once made equal to man, woman becomes his superior.
The man who says "I may be wrong, but -" does not believe there can be any such possibility
Owned and rode: Honda 100H, Honda MBX 125, Kawasaki AR 125, Suzuki RG 125 Pepsi, Honda NSR125 RK, Honda NRS 125 race bike, Suzuki GSXR 400 Bandit, Aprilia RS 125 O2, Honda CG125, Kawasaki KMX 125, Aprilia RS 125 O6, Suzuki XT225 and now Honda XR 400. ( A few scooters and other dead beats in between)

[lozza]

[lozza]

just some more info to help, the throttle needle is set on the 2nd notch from top

the jet size is 135

[SillyMe]

Correct, give all the holes a good blow out to with the lungs.

You want plenty of fuel in the float chamber without it spilling over.

(13mm on the NSR) did you scroll down and see the measurements and how to set the float hight. You hold the card upside down and set the measurements.

(13mm on the NSR) https://www.horizonsunlimited.com/hubb/yamaha-tech/urgent-help-needed-carb-leaking-50217

I think there is other info there too for screw settings.
idle screw, mixture screw ECT.
____________________
Once made equal to man, woman becomes his superior.
The man who says "I may be wrong, but -" does not believe there can be any such possibility
Owned and rode: Honda 100H, Honda MBX 125, Kawasaki AR 125, Suzuki RG 125 Pepsi, Honda NSR125 RK, Honda NRS 125 race bike, Suzuki GSXR 400 Bandit, Aprilia RS 125 O2, Honda CG125, Kawasaki KMX 125, Aprilia RS 125 O6, Suzuki XT225 and now Honda XR 400. ( A few scooters and other dead beats in between)

[lozza]

[SillyMe]

K. no worries, didn't know the year of your bike and though float hight on NSR's would be a universal thing. They must have changed significantly over he years.

If it runs ok over 4000 revs this indicated to me it may be in need of a top end rebuild. The reason I say this is because the faster two strokes rev the less mixture they lose through the exhaust port which gives a lot more power. This is why it may seem to run good in higher revs.
____________________
Once made equal to man, woman becomes his superior.
The man who says "I may be wrong, but -" does not believe there can be any such possibility
Owned and rode: Honda 100H, Honda MBX 125, Kawasaki AR 125, Suzuki RG 125 Pepsi, Honda NSR125 RK, Honda NRS 125 race bike, Suzuki GSXR 400 Bandit, Aprilia RS 125 O2, Honda CG125, Kawasaki KMX 125, Aprilia RS 125 O6, Suzuki XT225 and now Honda XR 400. ( A few scooters and other dead beats in between)

[lozza]

[SillyMe]

What you can do is put the bike into first gear and push it, if it moves easy enough and the back wheel doesn't lock up then it's likely to be a top end rebuild job. Compression will verify this if your able to have one done.

Also that would be low idle plus other carb related issues which your addressing and/or the top end of the engine andpower valve may be choked up with carbon.

Found these, you could give them a try .
Just wait for the time to elapse as a free user.
https://rapidshare.com/#!download|701|228170550|NSR_125_Service_manual.rar|63140

https://rs788tl3.rapidshare.com/#!download|788|362862382|pdftown.com_NSRmanual.zip|66188
____________________
Once made equal to man, woman becomes his superior.
The man who says "I may be wrong, but -" does not believe there can be any such possibility
Owned and rode: Honda 100H, Honda MBX 125, Kawasaki AR 125, Suzuki RG 125 Pepsi, Honda NSR125 RK, Honda NRS 125 race bike, Suzuki GSXR 400 Bandit, Aprilia RS 125 O2, Honda CG125, Kawasaki KMX 125, Aprilia RS 125 O6, Suzuki XT225 and now Honda XR 400. ( A few scooters and other dead beats in between)