Eric,

I am VERY grateful to get your feedback.

You are correct- I need to sit back for a moment, re-set and think what I've been doing. This fault findng process is a little exasperated by long gaps of work travel in between where some of the finer details of what I've done fall between the cracks.

I was very excited that I found the choke issue and really thought that was the issue.

So to address your initial reply.

I rebuilt the engine myself- with rebuilt cranks and all new OEM seals but I'm no expert so there's always the thought I may have made a catastrophic mistake along the way- however I am fairly confident the integrity of the engine is good because I very carefully performed a leakdown test and the results were the best I've ever achieved on an engine. Can't remember the exact numbers but it held pressure for a long time. In addition- I've just been an assembler in this process, the engineering such as crank rebuild and cylinder replating were done by experts....

I did a compression check just to make sure nothing mechanically had happened since I got it running such as a holed piston or cracked ring or something. The exhaust bridges have been mended and I was just wondering if maybe that repair had failed and in some way was affecting the compression. Both cylinders had identical PSI so that's good.

Anyway...as to which cylinder is the problematic one- it's always been the front. I think I was confused by the twisting and turning of the TYGA expansion chambers.

Thanks to your advice I think I have a new path which is...

1- The bike was performing quite well when the RC Valve controller was in Japan getting fixed. That was when I think I talked about it having a very narrow power band, and yes it was before I discovered the choke issue. I read somewhere that not firing after 4000 rpm could be a sign of the valves be maladjusted so I might try running the bike with them disconnected and held in place - and if both pull cylinders pull all the way to the redline then that will be interesting.

2- Love the idea of connecting a strobe and seeing if it still flashes all the way up the rev counter.

3- Will try switching the coils and see if the the fault follows the coil.

4-Will swap out the plug caps for new ones, actually, I have some brand new NGK red ones on my RZ500 which is sidelined with bad crankseals so I'll probably rob them. Been using the BR9ECM plugs for sure.

Thanks again for the time you spent thinking about this!!

Regarding the NGK caps, take a ohmmeter and make sure their resistance is same as the ones your replacing. I had a hard learned lesson a few years back. I installed a set of Nology coils on my bike and unknowingly used caps that had too much resistance. The bike was miss firing at higher RPM. I put the little stock coils and caps on and the issue went away. I eventually got two RS125 coils and things work great. My bikes pretty well sorted, but retired and literally on a shelf.

I think you can rule out crank seals at this point based on your measurements.

I believe NGK sell plug caps with and without resisters
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Why do things simply when you can complicate them

I use an NGK LB05EMH [part number 8160] on the top cylinder:



R5300A "shorty" plug and TRS1408F on the front, with the HRC head conversion.
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Andy.
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After a long spell working most days a week...test ride #238 revealed some progress.

I had a hard time testing the resistance of the older blue plug caps- because of course I didn't read the instructions and realized I need to test it while it's connected to the coil...I thought I would get a reading with the meter pointers touching the metal that would normally connect with the spark plug and the 'screw end' where the HT lead would go.

However I noted that my new red ones are nearly the same as Andy's so I'm trusting they are ok....but then again maybe not...that 5KΩ might be throwing a spanner in the works...read on.



Decided I'd try running it with the powervalves disconnected. Took off the tank- started it up and the servo didn't move no matter what the engine did. I randomly switched out the sub control unti that hangs on the right. No difference. I then looked and the black/blue disconnected wire. I thought well everyone knows that on the MC-18 disconnecting it de-restricts the engine by letting the RC valves operate in such a way that it releases more horsepower so there's no way I want to connect that again- but I did and hey presto the RC valve started working like it should as described on page 51 of the manual which is : at 2,000rpm the servo moves the pulley clockwise and then at 3,000 rpm it moves anticlockwise. I re-adjusted the cables so they have just under 1mm play. Then started it again to see it move clockwise and anticlockwise as described.

Put everything back together and had to take it on the freeway to get it to clear it's throat...and eventually it was running on 2 cylinders all the way up to 10,000 rpm when it hit a wall and was not interested in going farther. The good news is that it really pulls up to 10k and was fun to ride. If I didn't keep it on the boil though it would go back to running on one cylinder and then clear itself out once it was pushed. Sounds and feels like a duff plug but I don't know for sure and not sure why it doesn't like going past 10k....is that the domestic market restriction kicking in OR could it be the plug caps?

It's becoming hard to imagine this bike being a fun and consistent performer...


Speedo wasn't working....so after filling up with non-ethanol 93 figured out that the 'engine end' of the speedo cable wasn't inserted deep enough for the holding screw to capture it in place around the 'waist' of the outer of the cable. If you know, you know what I am talking about.



Grateful to have an original tool kit.


And then back at home....this happened...I blame a poorly designed cheap paddock stand....and me


position one in getting it back on it's feet...


I got off lightly with a decidedly second hand screen. Much less than the punishment I really deserved for being an idiot...tank, pipes, body work more or less untouched.


not giving up.

You may know this, and you may be experiencing something never seen before; I wouldn't rule anything out, but there are two black/blue bullet connectors... if you disconnect the wrong one... well, the RC Valves won't work! With both bullet connectors intact, i.e., stock, yes it will fall flat at 10,000rpm.

There are two different wiring harnesses for the 1988 models:

Type 1:



Type 2:



Ensure you only disconnect the bullet connector located closest to the rear lights!

More here, including an HRC video showing one version:

https://nsr-world.com/nsr250r-tuning/nsr250r-ignition/

Glad there wasn't too much damage from the fall. (Looks like just a bit of a scrape on the fairing?) 😢
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Andy.
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Andy!

Thank you! I know that wire well because I see it every time I take off the side panels of which there have been many, many times.

As long as I don't find much more damage than that well spotted nick on the fairing, (screen stays bent right back into place) tomorrow could be a lot of fun if I can sort out why both cylinders aren't running clean from low down.

Getting closer.

We have seen it before, where once a plug gets wet, it never runs well again. It can get expensive when that happens, especially with the R5300A shorty plugs! That's one reason why I only ever run the short plug in the bottom cylinder.

Seeing your photo of your LB05EMH cap, I see I am going to need to model in the "sprue" moulding under the NGK too now! 🤣🤣🤣
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Thnaks Andy...with that in mind I put in some brand new plugs...taking out the old ones was interesting...the rear (left in the picture) is running too lean for my liking....it's the front one now that's having problems kicking in...


as a reminder this is the jetting with a fully stock airbox
Keihin TA20A
No.1
Main 130 (Now 135)
Slow 38
Needle BPD, Power Jet 70
No. 2
Main 132 (Now 138)
Slow 38S
Needle BPE, Power Jet 75

So after disconnecting the correct black/blue wire here...


....I screwed the airscrew in 1 full turn on #2 carb to try and richen it a bit and took it for a spin.....but no good....front cylinder just won't kick in after 2-3000rpm- I know what you are thinking....one post I'm saying it was the front next post I'm saying it's the rear- to be honest I've a feeling it's switched- not sure...all I know is that, today, the front pipe is not as hot as the rear pipe.

Yesterday I DID try the timing light on both HT leads and it was flashing all the way up to 10,000 rpm- but hard to tell if that's accurate...but I'm beginning to think it's the coils so I parked it safely on the lift and that's probably going to be it for a while because we have to move house and I've been doing bugger all to help pack so....not sure what'll happen next but I have a new screen on order from Tyga so that's good.

This is the coil test procedure I'll try next...I've read from you guys RS125 coils work?..hard to know what I should test next....the carbs have been apart twice double checked for any obstructions...RC servo refurbed by T2 Racing...I now have a 2 full sets of black boxes.....PGM CDI, RC Controller, sub controller...and all seem to work...plugs switched out multiple times...plug caps replaced..


....next might be to investigate the pick ups (#4 below)...anyone using any upgraded reproduction replacements?


The decidedly second hand screen


No screen, no bother....


...if this bike ran on two cylinders it would be a rocket...

If timing light is flashing up to 10k you've got spark. As for adjusting the timing the stock bikes don't really give you any ability to advance or retard the ignition manually. The stock pickups are also adequate so no advantage in changing them as long as the are working. You might actually next try to look at the timing itself by pointing light onto the flywheel. That will require removing cover on left side. The flywheel will have the F and T marks on it. You will see the ignition advance as you Rev engine. Repeat for both plug leads.

The stock coils work fine, but the RS125 coils which are same as the RS250 coils are much bigger producing a better spark. If you search for Rs250 coils you may not find them or will overpay for a used set. If you search for rs125 you can still find new ones, just gotta buy two. You will need to make brackets for the RS coils as well as install connectors if you want a proper fit. I found this pic of my bike showing right side. Left is similar. It's not a trivial swap out so I'd think it's best to get yourself sorted with stock coils before going down this path.

I think that left plug looks fine. I know the mixture screws are difficult to get to, but you really should be adjusting them when the bike is idling. And, mixture screw not doing much once you get rpms up. They are totally out of the picture above a few thousand rpm.

Good luck moving. I'm starting my seasonal migration from Wisconsin to Texas today.
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MC28 SP

If you do end up replacing your coils make sure you get genuine Honda ones, on my Mc21 I blew several pgms before realising that a previous owner had fitted cheap no name coils and these were the culprit. It was an incredibly costly experience that I wouldn’t want anyone else to go through.

That's great advice Eric. And Zeus- that was really unlucky. Thank you both.

Yes, you are right about the airscrew. Don't know what I was thinking. Will twist it back. I have a feeling the coils are probably ok but thinking it might be an intermittent problem. Will do the test and see. Yes, I'm sure the stock pick ups are adequate- was thinking one of them might be faulty- but will try looking at the timing. Then I guess I'll just have to test whole loom.

Make sure the terminals on the harness and coils and nice and clean, and making good contact. Make sure the connections are nice and tight.

Also, once again, if you find it's dropping one side, swap the coils around and see if the symptom moves to the other cylinder.
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Andy.
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good idea Andy...dying to try swapping coils this weekend....and lovely job updating the lettering on that plug cap...I cant tell if it's a picture or art....all of the new site I've seen is cutting edge! brilliant.

Hudtm60 wrote:...and lovely job updating the lettering on that plug cap...I cant tell if it's a picture or art....all of the new site I've seen is cutting edge! brilliant.

Thank you for the feedback. Greatly appreciated.

There's a fair bit of 3D modelling gone into the revamp, some probably less noticeable than the rest. Admittedly, I'm quite happy with how some of it's turned out, like the spark plugs and caps. (There's an R5300A and cap in the tuning section that I think came out well... you may just notice NSR-WORLD "stamped" into the plugs!)
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