I've just moved the Members' Builds area out of the "Members" area and into the "NSR Discussion" area, to move/group relevant topics, and give them some more focus.

Please let me know (a) if you're OK with this by replying to this post so you don't lose any bookmarks etc.
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Andy.
NSR-WORLD.COM

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Hello Everyone,

It took a PM from Andy to get me to post again. Long story short, since October work got very busy AND had to move house. Everything fun got sidelined.

I last left the NSR with a to do list stuck to it reminding me to swap the coils to see if the intermittent firing on one cylinder followed the coil- but I haven't got around to that and ironically the time came to I move the NSR yesterday from the old garage to the new garage- it's a mere 7 miles. I figured that if I was gentle with it, it might play nice.

In terms of getting it from one place to another under it's own steam- the result was good. I wish I had video but I can't get the GoPro to talk to my new internet. In words: it'll run on two cylinders up to about 6,000 rpm IF I am very careful in only gradually opening the throttle, and that process can get you up to 70mph so that was kind of fun. However, like before, it won't tolerate a handful, nor is it interested in going above 6k on two. It's like it's a very weak spark that can't handle too much fuel before it gets extinguished-but I'm clueless to be honest.

Coil swap pending!

Still running around half naked.


In the new place on the old lift where it seems to have spent most of it's life. a real mechanics brain would help.

Hello,

back again after some hopeless purchases. I couldn't help myself getting a new stator via Jauce. https://www.jauce.com/auction/h1218235812 I've got it in my head that the problem is an electrical one and thought it would be great to at least take it out of suspicion even if the more educated would tell me it has nothing to do with the issue of only running on 1 cylinder....the rear one.




It even has an appropriate grommet..


swapping them out...



Getting ready to remove... the original coils.


...here they are....spoiler alert..these originals... aren't the problem...


with these other ones that arrived via Jauce...the problem is still there.


one has to wonder....is it the pick ups...or as they are decribed in the manual...Pulse Generators?


Good and Bad...just to remind me which one works and what doesn't. I've swapped out everything electrical apart from the pick ups which, let's be honest, they are probably fine....but has anyone had any issues? They do exist- but who knows if they work. https://www.jauce.com/auction/l1218608590


I think I'm resigned to the fact that it's a fueling issue so I think the next step is is to pull the carbs and take them to pieces, again, and also check the reeds while I'm in there.
To re-cap the front cylinder isn't kicking in....you can hear it trying at very low revs but it just won't catch. To be honest I've got nothing but time, so would consider sending the carbs off to a pro to go through them just in case I've been doing something wrong all along. it's quite possible. Whole thing is odd as for a very short and inconsistent time it ran on two.

Pretty sure I have the plumbing right.




In (brackets) is the stock jetting




Compression. Any compares?
Rear 120psi after 17 Kicks and throttle wide open- but engine is cold.


Front 115pssi after 17 Kicks and throttle wide open - but engine is cold.

Today I figured I'd swap out a PGM and I had a gut feeling about the airbox, so I took it off. Completely.

The bike ripped. At the bottom of a long hill I snicked into second and wound it up to the redline like a dyno run...it performed almost flawlessly....a little reluctant to get off 2000rpm mark but it was a clean pull to the redline. By the second run a neighbor was out in his front yard shaking his fist at me in a 'get off of my lawn' style. Mental note to move my test track. Such a perfect long slope though, but was just as well, might be running lean without the 'box.

Question was: is it the PGM or the airbox? I decided a decent compromise would be to sacrifice my spare airbox top and punch in four of those 20mm holes as depicted at the very bottom of here: https://nsr-world.com/nsr250r-tuning/nsr250r-carb-tuning/



Put it all back together and the bike wasn't as happy. Was fine once it hit the powerband and it would pull well to the redline but there was a lot of indecisive stuttering leading up to it....figure tomorrow I'll take the top off completely and see what happens. Why's this happening? Running too rich and losing the 'box leans it out? Not very likely. Or maybe I'm crimping some of the carb plumbing with the airbox in place? All i know is that I got a taste today of how the bike should be and it was great- just need it to be like that most days.

Here it is in testing mode.....only thing (legally) missing is the rear light...but I have one of them mercury switch brake lights on the helmet...so there's that.


Weapons Of Choice.

Here's a question: Do you lot know Dave Whattams...Mutt's Nutts? He's a well known genius in the LC world when it comes to setting up LC's in particular difficult hybrids. With his dyno and incomparable knowledge of what people will and can do with those motors he always finds a solution. https://www.muttsnuts2strokes.co.uk/.

Anyway, I asked if he would be willing to take a look at my carbs if I sent them over to him and he said : "looks like ifs an MC18 or MC21 model, always hard to tell from a picture, anyway, my point being doesn’t it have the solenoids on the carbs ? If it does have solenoids on the carbs, just try blocking the rubber tubes off for the front cylinder as if the solenoids fail they can fail open, which means the air corrector circuit is open and will cause it to be lean, hence poor starting/idling etc"

I suppose I should know the answer to this but checking in with you lot: does the MC18 have solenoids?

Answering my own questions here.

Yes the MC18 has a single solenoid for both carbs. (Later models have one each). Its mounted top right of the picture on a bracket it shares with the rear ignition coil.



Internally it is in good condition and moves freely. The question is if all the electronics that operate it are good.


and I only lost the spring once.


When I last took off the tank one of these hoses had disconnected itself. So I updated the clamps on the loosest ones and did my best to route as the diagram suggests…..


which to be honest...I'm not sure reflects the plumbing of an MC18...but I think I've got it as it's supposed to be.


Next step....coffee at my second favorite place with the air box top off...


Last edited by Hudtm60 on Sun Feb 08, 2026 8:07 pm; edited 2 times in total

At the coffee place. The performance is spectacular. Lifts front wheel going up hills from standing start at a traffic light. Have to keep it on the boil of course thru the twisties but that's cool. Must double check the jetting to make sure it's not dangerously lean- but definitely moving in the right direction.....if I don't get arrested first....I don't know how anyone on here retains their license. So addictive.

Without going into specifics, as it got me into trouble years ago [when someone else did it!], the MJ numbers written on the needle covers of your carbs look pretty big.

We've found over the years, stock NSRs tend to run rather rich (safe!), and removing your airbox lid entirely would seem to indicate this is so with yours. Bear in mind that the nature of the [dumb] "power jets" (PWJ) too, is that the harder/faster you rev the motor, the more fuel they draw. The idea with them was to use a smaller main jet, benefitting the mid-range/throttle response, and as the motor craves more fuel at higher RPM, it's progressively drawn through the PWJ. HRC blanks off the PWJ, and relies solely on the MJ and needle, hence the much higher MJ numbers in their base settings, which should give you a good indication of just how rich [safe!] stock settings can be!

However, we have found that with modern fuels [with some ethanol content], the slow jets often need increasing one size. Lean and rich can often have a similar "boggy" feel, but we've never gone leaner on the slow jets.
_________________
Andy.
NSR-WORLD.COM

Please keep all responses to Forum posts on the Forum so that others may benefit.

Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.

Check us out on Facebook! Please "like" our page!

Thanks Andy. I think I get what you're saying....knowing all that and looking at the state of my plugs and just feeling how it was running the other day I'm pretty happy with the current set up. Considering putting the airbox top back on again to compare it back to back but I don't want to lose that feeling!

I went out on it this morning and was not so happy with the acceleration. Had I been imagining how good it was? Deflated, I looked down at the rev counter....needle was dead on it's stop, indicators didn't work, temp gauge not registering anything, stopped, no neutral light, revved it while staring at the power valves- no movement there, which was kind of a relief- at least that explained why it wasn't wheelying in first anymore.

I took out all the fuses and checked them. None blown ,which was disappointing, but when I turned on the ignition back on...everything was back to normal.

Must be the fuse box. Will spray it with electronic cleaner, get a nail file in there, blast with cleaner and air and then maybe add a tiny bit of some di-electric grease to them later.

Didn't test ride it after the electrics rebooted....roads were a but iffy from the rain last night anyway.

In other thoughts on how to determine jetting: MuttNutts had this to say..."Modern fuels can take an age to colour up a spark plug due to the various detergents etc in it these days, so plug chops aren’t really a good idea as you could blow your bike up long before you get a colour indication of what is going on, also some fuels (like Shell VPower across here), doesn’t even give a colour most of the time

Luckily I have access to 97 Octane Non-Ethanol (Edit oops I had previously lied- it's only 90 Octane!-pic below) -so I'm hoping that helps my read of the plugs to be more accurate than if I was using standard pump fuel.

Got a new screen from Tyga and inspired by Nick's (Rothmans_SPud) VERY accurate Gardner tribute, (Nick also helped me get all the correct sponsor stickers), I will make one side of the screen American (Freddie Spencer) and the other side Aussie....(Mick Doohan)...with the appropriate flags next to the NSR logo, not as accurate as Nick's tribute but the effort is there

I don’t know what I’ll do with myself if this MC-18 ever decides to be as reliable as a reasonably priced car.

Here’s the latest minor irritation...

Signs of a liquid leak on the exhaust.


It appears to be coming from this unprotected opening on the right-hand crankcase which is is a weep/vent hole for the water pump mechanical seal.


You guys probably know Honda uses a double-seal arrangement on the water pump shaft:
One seal keeps coolant inside the pump
One seal keeps gearbox oil inside the engine
Between them is a cavity
That cavity vents through that small hole
It is intentionally open to the atmosphere.

I think the theory is.
If coolant seal fails → coolant drips out of that hole
If oil seal fails → gearbox oil drips out of that hole
It prevents:
Coolant mixing with gearbox oil
Oil getting into the cooling system
So the hole is a warning system, not a missing bolt.
What I see is a blue colored oil, which make sense because the oil is Motul Transoil 10w-30 (which is 'oil coloured' rather than red or green) and the coolant (Engine Ice) is blue....in other words both sides of the seal are leaking!

Oil + Coolant = blue oil.



Only supply I could find was Pattern ones via WeMoto https://www.wemoto.com/bike/honda/nsr/250/1988/121


I guess I'm not too surprised as I vaguely remember installing both those parts as being a pain....