OLD NS125R Supersport

[Guest]

Hiya

Just purchased a 91 NS125R supersport.Looking for ways of
de-restricting it.Ive checked the exhaust theres no restriction and also the intake manifold no restrition there.Bike goes about 75 MPH - 85 MPH
downhill.Cant find a pwervalve or such on the bike but there looks to be a bolt where it should be.
Anyone got any ideas on how the bike is restricted.Ive not check inside the carb to see if its opening fully.Exhaust seems to be standard issue.

Any1 got any ideas ?

Steve

[James]

Basically the bike isn't restricted but is a bit fucked up because back in the good old days when they were made they were still inventing various powervalve systems. My guess is that the ATAC chamber isn't blanked off. Behind the bolt on the right hand side of barrel is the ATAC chamber. This is basically a large chamber that increases exhaust port area. if you take off that bolt it'll probably come and stand alone. If you look down the hole where you've just removed the bolt from youll see a little hole leading through to the exhaust port. That hole needs completely blanking off. When this is done, the bike we'll feel sluggish and unresponsive at low revs, but as soon as you get above 6 and half grand it will really scream around to the redline.
At the moment you'll notice the bike has a progressive power delivery with no real powerband. Blank the ATAC off and it just screams through the revs like fuck.

Any tuning questions on this engine ask me. Ive stripped it and rebuilt it that many times i pretty much know the thing by memory.
Another thing, get a very big K&N and re-jet the main to 132. Woohoo, sweet when thats donw.

[Guest]

Thanks James.

I will have a look at that.Only thing is how do i blank off
the little hole from inside the big hole where the bolt goes into ?

The bike also seems to stuter alot around the 4.5k - 6k range any ideas what this could be.People have suggested it may be the needle jet playing up.
Any ideas ?

steve

[danny]

Ive got the fully faired model with single seat etc.
Ive got a micron exhaust & its in mint cond.Ive had just over 90 (tucked behind the screen). SDont know what the 0-60 time is but will see any 125 bike off the lights apart from an RS,Mito or NSR125R & just about any car.
I was told by a person on the sight(kieth i thinck) (and have done) that you take the bolt out the right side of the engine near the exhaust just above one of the radiator hoses. It has a long bar on with a circular block peice thing. cut the bar & bloch off & replace the bolt. this unblocks one of the restricter ports supposedly.I found that the mixture neede richening a bit after though (about just over a quter of a turn out on the piolet jet).


Any other tuning/derestricting ideas anyone, ive got a spare engine for her to, so can replace the atac valve if wrong.

did the engine last long with the bigger jet & filter. what oil did u run yours on james. any tips mate.

cheers

ps look further down the page for more info on this bike, named:
(NS125 any good)

[James]

I think your mistaken there buddy. If you cut the bolt thing off your doing the opposite of what i said to do. Besides which Steve, if your bike stutters between 4.5 and 6k it sounds like the bolt thing is already there blanking the ATAC off. If you cut the bolt thing off youll notice the bike will rev smoothly between 4.5 and 6k but will not rev round to the red-line as fiercely.

A while ago i attempted to make a site, a mixture of no time and couldn't be arsed stopped me from finishing it, but theres some nice pictures of my NS for you to look at. Copy and paste the link
https://www.geocities.com/big_jimbo2k/Bikepage.htm

U can see pics of how i bought it and building it step by step. well step by step until i ran out of film for camera, then some pics of bike as it is now.

Enjoy,
James

[Keen]

Nice bike, where did you get the new headlights? I think a single seat conversion would finish it off nicely, what do you reckon?

[Guest]

I shall have to remove the bolt thingy and see what its like.

For your info my bike wont even hit the red line in any gears.Its stops just before at about 9k.

Steve

[Kickstart]

[Guest]

Hiya Keith,

If the exhaust is restricted in some way then it must be at the back.Thes defenatly no tube or restriction on any sort at the intake.

Theres a lot of talk about ATAC.What exactly is this.And as james
pointed out earlier if i remove the bolt and cut it down will it help at all.

BTW its a fully faired 91 model excellent condition with 14k on the clock.
Blue and white very similar colors to James's.Cost 700 quid.I think i got a bargin really.Ill sort a piccy out.

Insurance is only 99 quid TPFT so its real cheap to run.

Ta
Steve

[Jolly_Thrasher]

Hey,

dunno if this is n e help at all but i have a 1990 NS125R-k full faired, its had a brand new barrel n piston and does 55mph at 6000rpm as i found out today as i just turned 17, it has a micron exhaust.

Apperently does around a ton top as the previous owner says. I

do find it very horrible at lows revs especially around town, is this because of that bolt?

Ben

PS, is it worth gettin the carb tuned up and having sumthing like a K & N fitted from what sum1 said about the airbox being restrictive?

[James]

Sorry Steve mate, forgot to mention that exhaust silencer restrictor. Basically if you look just after the stinger tail part of the exhaust there is 3 bolts holding the silencer to the pipe. undo these and remove the silencer. You'll see straight away theres a thick steel plate in the back of the silencer. This is a bastard to cut through cos of its auquard position. Easiest way if you can will be to get biggest drill bit the chuck in your drill can handle and drill through it in a few places.

When this is done exhaust note screams much sweeter.
Good luck anyway fellow old shape NSR basher
James

[Steve.S]

Thanks Guys for the comments.
Ive a few things to look at to see if i can get my baby any faster.
Hopefully ill be able to actually get the bike to reach into the red line.
Ill check the bolt out first then examine the exhaust system silencer.

Oh btw that should be a small piccy of my bike as ive just registered.
Great place for info.

Many Thanks
Steve

[James]

By the way Steve, just to clarify cos its getting complicated. I am NOT, i repeat NOT, saying cut the ATAC bolt bit off. I am saying the opposite, if its on leave it, and if it isn't then blank off the hole into exhaust port that it should be blanking.

Hope you undertsnad that buddy cos i didn't and i wrote it,

..ill have a whopper with cheese please, woh, where am i?
Confused me?

[Steve.S]

Yer James i did realise i miss quoted you on that one. :D

Thanks
Steve

[Kickstart]

[Guest]

On the NS its definately easiest to junk the std pipe and get an aftermarket perf pipe. Question is which one? Micron, Giannelli, Nikon. It would be nice to see a test of all the pipes to see what power characteristics that they give. Dont forget that a cheap easy mod for a touch more power is to fit Boyesen or carbon reeds, and even have the reed block ported for better flow.

[Steve.S]

Hiya

Just to let u know ive removed the bolt from the chamber.Its got a 2 inch long thin shaft attached to the end with larger 1/8 inch long shaft at the end probably acting as a plug.

After looking in the hole i could see a smaller hole which looked like to be going up and at the end of the hole was another hole which looked like it was in the exhaust manifold.So the plug must stop exhaust gasses from coming from the exhaust and up through the hole at the top.
This would also work the other way i suppose it would let gasses travell down the small hole from above into the exhast port if the plug was sawn off.

I havent sawn it off as i dont know what the consequenses are in doing so.
might try and get hold of a nut which will fit so i can keep the original one intact to see if its any different.

As for the exhaust theres about 10 years of rust corroded around the sliencer and i cant even tell if its a hexagon nut or allen key type screws

Anyone got any more info on the above situation?

Thanks
Steve

[Danny]

I had the same problem with rust round the silencer so i bought a Micron stainless full system from demon tweaks £99.00 in sale (www.demon-tweeks.co.uk or 01978 664447).
this total derestricts it but mine still had a silence restricter in the form of a long bit of pipe going into the expansion part that was held on in the middle by the expansion to silencer bolts (it will sound really tinny if it has one) just remove the silencer take the pipe out & refit silencer.
It sounds nice then & looks mint.
I turn my pilot mixture 1/4 of a turn out to richen it a bit but it may not be necessary.

PS where can you get boysen race reeds now- M&P have stopped selling them.

cya

[James]

Dont cut the bolt down. If you do youll lose all your top end high rev power and just have bottem end power. This is no good to man nor beast when you need to get past a line of Nissan Micra's full of grannys.

Its upto you but id personally leave alone and sort your exhaust out.

[Brook]

Hi i have a NS125R-L, and i ahve had 98mph out of it. it is a 1991 J-reg with a single light. what can i do to improve the accelaration on it ? its ok but ive been beten by the same bike and he shot past me (im jelues!) I need more top end and accelaration. is it possable or am i been gready? I have allready put a micron on it (sounds ok) tryed a K&N but it was shit and it blocked all my jets! what would happen if i did the bolt thing on teh side of the engine? TXT BK ASAP THANX!
Brook HUDDERSFIELD>

[Steve.S]

Mines a 91 NS125R-L as well.Im lucky to hit 80 mph.So what have you done to yours to improve it that much brook.
Maybe your teeth are in favour of top end speed rather than bottom end.
My mate also has a NS125R i seem to wip him on acceleration up to about 50 MPH but then he overtakes and shoots off into the distance.
Im prety sure his exhaust is derestricted though as it sounds quite a bit 'popier' and louder than mine does.

Steve