NS125R K Rebuild & De-restriction

[Simonbt]

I've been reading some of the questions people ask about this bike and i thought i would take some photos of the rebuild and hope that it helps others.

This is the first time ive done this to a ns125 so im gonna be asking a few questions of my own.

This bike has an allspeed exhaust and as far as i know that is all the de-restricting it has had. I know a lot of people have been curious about this ATAC valve so here is my first question....

PICT0044

Is the bit i have arrowed to in the photo the ATAC chamber? Should it come undone? i have tried but through fear of breaking it i have given up. If i put my finger in the exhaust port and towards the arrowed part from the inside it just feels like a small chamber.

PICT0035

Stage one. I have stripped all the bodywork off. The bike failed its MOT on both front and rear shocks (no damping) so they have both come off. I have removed the wheels for two reasons. One because i cant remove the shocks and forks without doing so, and so they can be repainted white.

This is a bit of a project for me so i will keep you all updated with what i do. If anyone wants me to take any photos for curiosity then just ask and i will do.

[Robby]

I used to have an NS just like that. Can't even remember what reg it was now.

Anyway, a few little suggestions and tips.

Most importantly. The wheels. Do them black. White wheels will never, ever be clean, and they are a bit of a funny shape on the NS making them a bitch to clean. I always wanted black wheels for mine, I had white ones.

The ATAC valve is in that chamber, but it might not have it fitted or connected up. Pretty sure theres something you can do to either leave it always open or remove it, on the standard bike it worked as an exhaust restriction. Keith (kickstart) knows, so wait for him to come along and say.

I'd do a top end rebuild on the engine while you have it stripped down that much, unless it had one very recently. If it had one in the last 5k I'd still put a new set of rings on, you're stripped down that far already and swapping rings is so easy it'd be silly not to. Otherwise those engines are quote tough, I sold mine with about 18k on the clock, Judging on how it was running I think it would have needed a piston and rings at 20k.

Another note on de-restriction. A lot of people drill some holes in the airbox lid, apparrently this helps. I assume the airbox mouth is fine for 12bhp, but struggling to supply enough air for about 20bhp.

[Simonbt]

One of the prevous owners had hand painted the wheels black and in my opinion they are horrible. This is a bit of a hobby for me so im planning on getting it back original. I've found somewhere that will clean and powder coat the wheels white for £35 which i think is resonable. Compared to my old 2000 NSR125rr the wheels on this are very easy to clean.

I am planning on doing a full engine rebuild, top and bottom. The top should come apart very easily. One of the previous owners still has the spare engine that goes with this bike which im picking up tomorrow. I'm taking the crank from that and getting that rebuilt. I'm getting the barrel rebored and relined and the crank refurbed for £290.01. That includes the following

- Barrel rebored and relined
- Piston
- Piston Rings
- big and little end bearings
- Conrod
- Crank Bearings and oil seals

So im expecting the bike to be off the road for a month or two but then be sweet when i've done.

For all those poeple thinking why bother.......... I'm Bored and i enjoy it

[Simonbt]

Just read your post again and noticed id forgotten something.

Ive not done anything to the airbox yet as i'm thinking about adding a K&N. I will be back with questions about rejetting it if i do.

[Robby]

Personally I wouldn't fit a K&N. The stock air filter flows quite enough air - I think its the same sort of size as one from a CBR600, which can flow enough air for 100+bhp with no trouble. K&Ns also filter worse than a stock one. The airbox is restrictive, but the filter isn't.

Those wheels are horrible, that finish is terrible. At least have a play with other colours in photoshop (or get one of the kids on here to do it for you) before getting them done in white. It might look ok in red.

And a few questions just to determine if it was my old bike or not, its possible.

Is the mileage over 18k?
What year is it? I think my one was E992 MHX, but that may have been my VFR400.
Does it wear fiberglass front fairings?

And seeing as you're doing all this work to it, please don't sell it to a 17 year old learner to thrash and destroy afterwards.

[Simonbt]

lol. I think it is your old bike. Its got a fiberglass upper fairing on it, its ok 25k on the clock (wow, i know!) and its an f reg. Has everyone had a go on it!! haha

What should i do to the air box then? I dont really wanna drill holes in it if i can help it. (the K&N i was looking at is a cone shape something like the one below)

[Robby]

Keep the stock airbox on - those little cone filters are no good in the wet and can often give worse results. Airboxes work well by having a supply of still air to gulp down.

Stick with the stock filter and airbox to start with, see how it runs.

That may well be my old bike, I can't remember its exact reg. Last time I saw it I sold it to some bloke from dartford.

Trying to think of other traits it posessed. Lots of purple 2 stroke oil spilled down the inside of the front fairing from trying to fill it up in the dark, radiator was a bit shitty in the middle, had the single seat thing but not the tailpiece fillet, and the panels didn't seem to quite line up properly. Had white wheels with peeling powdercoat and slightly scuffed purple bar ends when I had it.

Thinking back, E992 MHX was one of my cars. This may have been my old bike, have to hunt through the assorted old paperwork to see if I have its reg written down anywhere.

Edit - just looked, My one was G657 BLE.

[Simonbt]

nope, its not this one. this is a H reg.

Anyway back to the ATAC chamber. Ive now picked up a spare engine. The ATAC chamber on the original barrel is open and the chamber on the spare one is closed, should that bolt (shown in one of the pictures above) come off?

[Robby]

I think so. Read something a long time back about undoing it or twisting it 90 degrees to make the bike faster.

Take it off an see. I have a feeling its got a rod with a blanking plate attached to the back of it, and you just cut off the blanking plate and put the bolt back in the hole.

So you don't get a proper powervalve out of it, and should get a fairly evil powerband.

Of course, this is just stuff I read on the internet about 3 years ago, so I'd undo the bolt and see what you get. Take pictures.

[stevo as b4]

It's a different engine to the MTX that im thinking of, but where your were pointing to the side of the barrel on an MTX that is where the drive linkage goes from the governer to the ATAC valve, and a rubber boot fits over it. The ATAC resonator chamber is actually located in the cylinder head, and is a round vertical tube shape with a plastic cap on the top. I think the NS would be similar, so maybe thats a blanking plug for what would be the linkage on a full power bike?

[Simonbt]

Well i have a barrel with the blanking plate intact and one without. So when it is sorted i will see which one is best.