Does anyone out there know anything about the NS250 motor?
Does anyone know any easy ways to extract more power from the NS motor??????

The 1984 RS250R it is based upon made 67hp @ 11,750rpm and 4.08kg-m @ 11,500rpm vs the 45hp @ 9,500rpm and 3.6kg-m @ 8,500rpm from the NS... so hopefully there are more revs to be extracted.....
The bore and stroke are the same......
Does it suffer the same problem as regards the lower pipe on the NS400R, where it has been shortened to allow chain clearance? Would one of the Terry Shepherd or JHA lower NS400R pipes fit and allow the engine to rev to 11,500rpm and hopefully get more power that way? Can the ignition be advanced? Are carbon fibre reeds available for it, and would these help?

I know I've asked this in other posts but I thought it would be visible to more people if I started a new thread.

Andy, Jeff said he thought you might be able to help.....

I can't be the only one out there with an NS!!!!!

If anyone can help or answer any of these questions please let me know

Phil

Try ns400r forum. Theres one guy there that has ns250r.

I would imagine the NS250 would respond to rather more taditional methods of tuning, but I haven't ever even seen one, let alone seen inside one!

You're certainly going to need to get some barrels to play with, or bite the bullet and pull your barrels off for some investigation.

I know the ATAC system was never that efficient on any of the motors it was used on, and imagine it's pretty much the case with the NS250. A set of race pipes and larger carbs (the MC18/21 carbs can be modded to fit the NS400, so maybe possible with the 250 too?) and some slightly more aggressive porting will all probably help things.

I'll see if I can find some info, but I think any race parts and books for them are long gone! I think RS250 ND5 parts may be worth looking for to give you some ideas of where to go.
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Andy.
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If you compare the MC16 to it's RS relative, the basic design is the same, but the porting on the NSR is very reserved. I suspect that this is the case with the NS250.

I would imagine that the only way to extract more power is to pull the barrels off and get in there with the grinder. Then you'll need pipes, and probably carbs......and then an ignition.....and so it goes on.

I'm sure that when Honda built the NS250 they wanted it to be reliable and reasonably easy to ride. When they built the RS (of that era) it had to win races. There's a huge difference.

I don't have the 1984 port specs for the RS, but I do have the 1985 specs which may be similar, so if you get the chance to whip off your barrels we can have a look to see the differences.

At one stage there were some 1984/85 barrels for sale on ebay. I think the guy also has some other parts that he was trying to sell. I did talk to him and he seemed to have quite alot.

I dont have his contact details here, but when I get home I will dig them off my computer. Might be worth getting a cylinder off him.
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If I have to take the carbs off once more...

Thanks everyone for your comments. I'm not looking for RS levels of performance Matt@TYGA, as I don't want to rebuild it every 500 miles - but an extra 5-10hp wouldn't go amiss.....
If I can get 5hp by new pipes / new reeds / airbox mods that would be fine by me; maybe one of the Terry Shepherd NS400R lower pipes (that does away with the ATAC) and a new rear cylinder end can would be a good start?
Unless I can get some 84/85 RS250 pipes and other bits of course....
Next step would be new carbs.....

My understanding (from my old 350LC days) of 2-stroke tuning of bikes of this vintage was that the top end revs were restricted by engine breathing, i.e. airbox / carbs / reeds / pipes. I am sure the NS250 airbox is much less restrictive than the 350LC one because of it's better packaging, so I expect there is no value-add in Ramair filters, and drilled airbox / carbon reeds / pipes would be the easiest gain. Any guess how much I would get by this alone?

I'm not too confident about grinding the ports as I am sure I remember from the time that (on the NS400R at least) that you risked chipping out the Nikosil cylinder coating and wrecking the barrel?

The bike is no slouch as it is (especially on 14 / 44 gearing instead of the standard 15 / 42), but more power is always welcome.........

Thanks too for everyone not shouting me down for it not being a true NSR!!

Phil

philandhisjag wrote:Thanks too for everyone not shouting me down for it not being a true NSR!!

Phil

It's a sporty Honda stroker, it's near enough!
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Please do not PM me technical questions, if you can't find it on the Forum start a thread

It's of the same bloodline anyway........

Thanks everyone again for any help, I am sure you can imagine the trouble I'm having getting info for it (I have a Rothmans NS250F), because:

a) It was never an official UK import
b) It was only produced for 1985-1986
c) The F model was less popular
d) The Rothmans one was a special edition - the Rothmans NS250F has the Astralight wheels of the NS250R, rather than the comstars

So I have a limited edition of a rare bike that was only made for 2 years and never an official import......

I think it shares some common components with the NS400R, so I have downloaded a copy of the NS400R manual from the NS400R site.

I was thinking of upgrading the suspension and wheels to something more modern, but by the time I do that it would probably be cheaper to buy an MC16.... plus my riding is not that hot (I'm not racer, more an urban nutter from my 350LC days) so I wouldn't appreciate the difference and it would end up just being a cosmetic exercise.

I just want a bit more power for point-and-squirt around town, and motorway jaunts which cover most of my riding as I live by the A1 / M1 interchange and work in Liverpool or Coventry / Leamington Spa.

15 / 42 geared it for 125mph which meant it wouldn't rev out in top.
15 / 44 made little difference.
14 / 44 is where it is at now, which I am hoping will have geared it for nearer 115mph revving out in top; it would just about this pull before in 6th without revving out, maybe 8500rpm (but it took favourable conditions, and a long wait from 100mph). This gearing should give better acceleration too.

115mph is more than enough for an unfaired bike!!!

All the best to everyone, enjoy the bank holiday weekend (in the UK)

If anyone is over that way, you might see my bike at Squires in Sherburn-in-Elmet sometime over the weekend - if you live in the North / North East you will probably know it.......

BR

Phil