Ns125F '88 Project

[BradRapheal]

Hi There, new to the forum!

Basically, i bought the Honda NS 125 (2 stroke!! ), and was thinking of tuning it and making it maybe like an on road track bike/streetfighter style, although there are a few queries with it... so i have a few questions, any help will be appreciated

1. apparently the engines can be made very powerful for a 125, (40BHP i was told, i am sceptical) can anybody clarify or give an estimate/ there opinion? (i know tuning 2strokes to the back b*llocks makes them quite unreliable, but i only want this as my weekend/fun bike, and will be looked after so should be okay lol)

2. Wheels. The rear wheel is too thin in my opinion, it makes the whole bike look really thin and doing over 70mph on it worries me :') , so my original thought was to just change the back wheel, but there is only a few mil each side of the tire to the swingarm...
So i thought about changing it to an Aprillia RS125 swingarm + back wheel as the wheel is much wider.
does anybody know where to get dimensions for said swingarm? as google didn't give me any answers, or any other rear ends that may work the same?
Also i plan to also change the front end of the bike as well, but that will be less of a ball ache.

I understand people will probably tell me to keep it original and i would agree, although the bike wasn't in the condition i thought it was in when i bought it, basically been gypo'd together will cable ties and it was my second bike, so didn't know much better than to check things like that lol.

Always wanted one of these bikes since i was a kid, so one way or another i will make this bike awesome. just gathering the data before the hard work starts lol

Sorry for the essay and once again, any help / knowledge thrown my way will be greatly appreciated thanks for reading!

[redeem ouzzer]

Fireblade front and rear end fits.

Engine isn't that tuneable (or strong).

Note that putting wider tyres on will just show up the lack of frame stiffness.
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Be a REAL MAN!

[-]

The early NS125F will be capable of around 22bhp max re-restriced.

The NS400 was only around 65bhp and essentially 3 overbored NS125F barrels.
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TZR250 2MA road, TZR250 1KT road, TZR250 2MA race, TDR250, YZF-750R Boost colours.
Jaguar S Type 3.0 V6 Sport R, VW Transporter T5 GP LWB Shuttle 140ps DSG.

[V2]

I had one of those! After getting it running it made about 18bhp on the back wheel, The previous owner had fitted a bigger carb and a custom tuned exhaust with spanny chamber (40bhp ) I think the Honda RS125r only stuck out just over 40bhp so I suppose its doable but probably not on the average mans budget

[BradRapheal]

well i was looking at my bike on google and they come out the factory with 22bhp, restricted. so i know it will go higher than that...
mine has a allspeed one piece exhaust on it, i don't know if been jetted to fit tho, runs nicely though.

the fire blade front/back end sounds fun lol, ill look in to that

and budget wise, like i say i plan on keeping it for as long as possible, so i have no time limit for what i plan to do, so hopefully that makes saving money for it easier lol

[Hahadumball]

i also had one
it also went through 2 bottom ends and 3 top ends and many rebuilds

20bhp or so tops and not that tuneable
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Fin: no matter how much I look at It I can't understand what was going through my head, all I remember is going about 80 and redlining it to stop it seizing.
360 Deg... Five 1/4 turns. :- Teflon-Mike 18 Jan 2015

[V2]

Fair enough! Mine was pretty good for a 125 running at 18hp! however I just has a look at the rs125r and that makes 45hp, a quote from the interweb:

[stevo as b4]

Not so sure it's worth radically modifying an 80's classic 125 to make it a special or track day bike IMO.

I'd look at simple mods and just getting the suspension and brakes working well and use decent tyres in the original sizes or close to them.

Style wise I'd keep all std bodywork as you'll never make a nice but dated spindly old 125 look like an RS125 or ride like one.

I'd forget Aprilia RS swing arms etc. If you want to change wheels or forks, you'd probably have alot more luck and less hassle looking for NSR125 bits.

Motor wise, they are ok IMO. You'll get a bit more power probably 25-26bhp with a good/custom pipe and a programmable ignition.

If you really want to play with a engine, then I'd get a crank rebuilt with an uprated big end and or rod, and then fit a Malossi 190cc big bore kit. You'll need a custom pipe to make the big bore work to its potential.

The more you tune the less reliable it'll be or the more often rebuilds will be needed. If possible I'd look out for a spare engine or bottom end that you can strip and rebuild at your leisure, so if it does go bang you'll have the bits to change engines or top ends to get it running again asap.

I've got 3 KMX engines near enough in bits, but could use a spare bottom end so I can build a 125, a 200 and have a spares engine to raid for bits if one goes bang.

[MarJay]

Will be mega crap as a track bike. The frame is steel tube, just because it has a box cross section doesn't mean it's a good frame. The wheels being thin makes no difference to how fast you can or cannot travel, or how dangerous travelling at those speeds is.

What makes travelling at those speeds dangerous is the flexible frame that induces weave at about 80mph. The reason I know this is because my very first bike was an NS125R.

Mine was tuned by an expert mechanic who also happened to be the previous owner. I'd be surprised if it made more than 20bhp with a Micron exhaust and other mods.

I have bikes that I used to own that I'd love to own again, but my very first bike, the NS is not one of them. It just wasn't all that. It did me as a 19 year old but I can't really see any reason why anyone would want one now other than for nostalgia reasons. The Alcast NSR125 or the later foxeye NSR yes, but not the NS, and especially not the spindly naked 125F which you can see so much light through the frame that you might as well be looking at a bicycle.

Don't modify it, ride it for what it is, or sell it. Or ignore us, I'm not sure I give a sh*t enough to worry either way actually. It's just that shit a bike.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[BradRapheal]

The only reason i wanted to put a different swing arm on the NS was to have a thicker back wheel, i don't really plan on making it ride or look like the RS125, just the back wheel has more stability. The shoulder of the tire on the NS is about 1cm thick, there isn't much tire on the ground.

as for the body work i wanted to keep it looking as the bike it is, not trying to make it into anything else, as i say i just think it will ride bit nicer with thicker tyres

and tbf, i guess i worded myself wrong, not a track bike, but a nice quick bike, the looks nice lol. it isn't an ugly bike IMO, but i just want to make it my own

i have been looking for bigger cylinder kits/big bore kits for them, but couldn't find any... is there anywhere i could be shown that sell them?
although as the bike goes, its not slow. it doesn't NEED to to any faster than it already does, i more just want to make it ride nice so i can have some fun.

[MarJay]

[BradRapheal]

*shrugs shoulders*

if your doing 80mph, would you rather your tire be roughly 5cm touching the ground, or 10? (not exact figures but you get where I'm coming from)

so your saying that if it has wheels, no matter how thick, that it doesn't matter? would you do 80mph on a motor bike with bicycle wheels?

[MarJay]

[Hahadumball]

https://cdn.velonews.com/wp-content/uploads/2014/07/5_20140727_%C2%A9BrakeThrough-Media__KRC4999.jpg

your theory explains why tour de france riders who go fast and corner fairly sharp use super mega fat tyr.... nvm
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Fin: no matter how much I look at It I can't understand what was going through my head, all I remember is going about 80 and redlining it to stop it seizing.
360 Deg... Five 1/4 turns. :- Teflon-Mike 18 Jan 2015

[Kickstart]

[MarJay]

I assume we've either convinced the OP not to change his wheels for wider ones... either that or we've convinced him to not come back on the forum.

I can't even begin to explain how I feel about "Wider tyres must be more stable". Jeez, I'm turning into Sickpup...
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[ZX-7R]

[-]

[stevo as b4]

Not wanting to be too autistic here,

But a full power 22bhp NS125 with working ATAC will be unlikely to be a true 20bhp at the back wheel or more, though this depends on the dyno massively, and if your one of them people that believe that all manufacturers under/overstate crankshaft bhp figures.

Also someone said allspeed or could for that matter be an off the shelf 25-30yr old design of aftermarket pipe, being likely to increase power. Its not often many off the shelf pipes do much to increase power alone, and if the mid is good it'll be crap at the top and vice versa.

Secondly a 22bhp NS would be fun enough to ride, and have an interesting power delivery and be a genuine 85mph bike too.

Lastly looking at shit sites like bikez, bike pics etc and magazines are all full of shit, and only quoted specs by the manufacturer I personally believe in.

[Kickstart]

[BradRapheal]

Yes it was Bike specs i was using, and i quoted it wrong it says 25bhp, (link to that page at bottom of paragraph) apologies for using what i didn't realise was an unreliable source.

https://www.motorcyclespecs.co.za/model/Honda/honda_ns125f%2083.htm

"I assume we've either convinced the OP not to change his wheels for wider ones... either that or we've convinced him to not come back on the forum"

No, didn't convince me not to come back, just showed me the types of people on here, and on my first thread. As i said this is my second bike, and the first one i plan on playing with. I come to the forum asking for opinions and guidance and you speak down to me, taking the piss. you could have gotten your point across with out being an arse

"Secondly a 22bhp NS would be fun enough to ride, and have an interesting power delivery and be a genuine 85mph bike too"

i have had not much over 85mph out of mine, got up there quite quick tbf aswell (in my own opinion, then again its the only 2stoke 125 I've ridden so maybe thats why i think that...) but it was slightly shaky, hence why i thought thicker tyres may help. I'm sure there 110 thickness on the rear wheel.

i do thank people who are putting opinions and facts eat and not being what i feel is rude to me. these are the type of comments i came here for.
Also i didn't realise the RS chain would be on the other side, thank you for pointing it out

Either way, I'm customising this bike, wether every idea i have for it is a good one or not, doesn't mean that every idea i have will end up on the bike, doesn't mean its a disaster from the get-go.

there's a couple pics 's of the NS incase anyones interested. lol

[V2]

This was my one!

https://cdn.bcf.44bytes.net/files/img_3021.jpg

[MarJay]

[Kickstart]

[MarJay]