'87 Honda NSR250 'ELF Special'

What reeds are you using?
Not sucking gearbox oil into crankcase?
Float level isn't too low?
Air jet solenoids stuck or wired backwards? (closed when they should be open and vice versa)
 
Thanks for the response crazypj.

I'm using the original OEM reeds, they still seal well, but this is an area I do want to upgrade in future. I wouldn't say the crankcase is leaking. I had a look inside and it's spotless, it isn't using oil, and it has new crank seals and HRC recommended Threebond 1207B to seal the cases. Plus it starts very easily and idles well. I've set the float height, but it would be worthwhile rechecking it. I think checking the air correction circuit for functionality and blockages will be a good next step.
 
So I noticed that the choke had become stuck against a hose retainer and was jammed on. I sorted that, and it was running better, but still seemed very rich on the upper cylinder. So I pulled the hoses off the air solenoids and fuel came out of the one leading to the upper cyl carb! No idea how fuel could have got in there, but I've dried it out and reassembled the air jet system. After that, it's now running a lot better. Still on the rich side and the plugs are a bit oily but that's expected since I'm still running premix 30:1, far too oily for the short low speed test runs I'm doing.
 
Look what showed up in the post. Swingarm bearing, 9 MONTHS AFTER I ORDERED IT! :eek:

 
You will need to rejet your carbs for the non-stock pipes you are running plus any mods to the air box you have done. Simple power mod is to drill two 40mm holes in the upper lid of the airbox but rejet with plug chops if you do this or you will run lean and seize!

Fwiw, the mc-16 engine is rigidly mounted to the frame, all other nsr250's are rubber mounted. The mc-16 is also much narrower than later models so fairings and tanks need to be modified to fit. How do I know this ;) have a stock mc-16 in the garage along with a modded mc-21sp.
 
Canuck13 said:
You will need to rejet your carbs for the non-stock pipes you are running plus any mods to the air box you have done. Simple power mod is to drill two 40mm holes in the upper lid of the airbox but rejet with plug chops if you do this or you will run lean and seize!

Fwiw, the mc-16 engine is rigidly mounted to the frame, all other nsr250's are rubber mounted. The mc-16 is also much narrower than later models so fairings and tanks need to be modified to fit. How do I know this ;) have a stock mc-16 in the garage along with a modded mc-21sp.
Click to expand...

Are you that Brian guy from nsr-world? I figured I will need to re-jet, but I've just been avoiding full throttle for now. The problem at the moment isn't running lean, but running rich. It's fouling plugs on the upper cylinder just about every time I cold start it and warm it up. Runs well when it's warm if you keep the revs up, still has blacks plugs though, and will start to miss on the upper if sitting at idle for too long.

My MC16 has an MC18 motor, so it's got the rubber crankcase mounts but is solidly mounted to the frame.

As for fairings, I've been flip flopping around trying to figure out what ones will look right. It's definitely gonna be RS fairings, just not certain on which year. Here's the latest photoshop with an 87 RS front fairing, and a 92 tail. Though I'm not sure about the tail.

 
Nope that's not me :)

Use same name there as here. Check your air filter and pull the main jets to see what ur running. Also check your idle screw setting. NSR world has the factory settings listed. It sounds like yours are too far out. Something is not right. Also confirm you have a full charge in the battery! When mine is down, even a little, I have spark issues resulting in dirty plugs.

Cheers
 
Small update. I think I have solved the problem of the plug fouling. I noticed that the upper cylinder was misfiring. The misfire was very bad at idle and low rpm, but would improve as the revs picked up. I initially thought electrical, so I tried swapping the coils, but this made no difference, and neither did a new plug. Battery is brand new and fully charged. I reset the idle screw to factory settings, and re-synced the carbs (visually) as I had been fiddling with these settings to try get things to improve. The changes made a small difference.

I figured it must be fueling so I pulled the carbs off again, a bit of an annoying job with the oil pump attached. Carb settings were as I left them, stock standard. Also, the air filter is brand new. I then checked the air correction circuit connections for blockages. No blockages, but I noticed something I had missed when installing the system. The 4 way connector has a small brass jet on one of the connections to restrict flow. I looked at the diagram in the manual and I believe I had the wrong hose attached to this connection. Swapped a couple of hoses around and put everything back together.

Huge improvement! The exhaust pulses now feel consistent out each muffler. And there is the same amount of smoke from each side too. Misfire is gone. Still, I only took it for a 5 minute ride. I'll see how it starts and runs tomorrow morning.
 
Nope not sorted :( I have solved the misfire problem, but it's still killing the top plug every time I start it from cold. I'm going to replace the float valves, as they may be weeping. I'll also replace the needles as they look pretty worn.
 
Replaced the needles, float valves, air screws and gaskets with the ones from the kit. Slow jets and emulsion tubes are different from OEM so I left the old ones in. I've also put in 140 mains to be on the safe side with the modified airbox lid and aftermarket pipes I'm running.

The bike now runs much worse! It won't run for more than a few seconds, and that's only on full choke. Only one cylinder seems to be firing (the problem cylinder). I'm guessing the needles which are not the same as the standard MC18 ones are now completely blocking the main jet at idle/low throttle, and my pilots are too small to supply enough fuel. Either that or I created an air leak somewhere when reassembling the carbs. I've ordered pilot jets in the next two sizes, so I'll see what happens when I fit those.

These motors are so damn sensitive!
 
Ok so the cheap carb kit isn't shaping up to be such a great buy after all. I've now gone up two sizes on the slow jets, and after fiddling with the air screw settings have got the bike to idle and rev freely. But it still feels very lean. There's no power or torque at low to mid rpm, it's basically still unridable. I still think the new needles are to blame. I pulled them out and compared to the old ones. They are the same length, but the new ones have a significantly different profile. New needles measure 1.35 mm at tip just before it tapers to a point, and the old ones 1.15 mm. Sure the old ones must be a bit worn, but I doubt they were 0.2mm larger when new.
 
I've been taking a real good look at some of the parts in cheap re-build kits.
The finish isn't very good but can be made to work.
You need a x7~x10 jewelers loupe and check the machining then a set of micro drills and pin vices plus fine needle files
There are various burrs that need removing and check actual hole size with the 'plain' end of drill (they are cheaper than buying a gauge wire set)
If your going to mess with two strokes you'll probably need them again so it's probably worth the investment
 
Thanks for the tip crazypj, you've always got some good advice. However I can't see myself investing in these tools any time soon. I've come to the conclusion that the jet kit was a bit of a waste of time, I couldn't even use the new gaskets as they just swelled up with petrol. I pulled the needles out and they are actually made to suit the later model MC21 carbs. They actually looked like they were finished to a pretty decent quality. They may even work ok with some shimming done to raise them slightly, but for now I've put the old ones back in.

So with old needles, new float valves, 140 mains, and back on 38 pilots, the bike is strangely still not right, but it's noticeably better. Maybe my old float valves were the cause of my initial plug fouling problems? Anyway I've put #40 pilots in and tomorrow I'll do a proper jetting procedure for the slow running circuit, none of this haphazardly changing setting to see what happens shit.
 
Here are the results of today's jetting day. I focused mainly on the slow running circuit (pilot jet and airscrew).
- Started with #40 pilots and the bike would idle, but bogged or stalled as soon as I opened the throttle.
- Turned the airscrew in almost completely and the bike would rev, but had no bottom end power, and just ran terribly.
- Up to #42 pilots and it runs better. Still no power below 4.5-5k.
- Decided to tape over the holes I made in the airbox lid and suddenly my low end power is back. Not as much as before I rebuilt the carbs, but the bike is now usable.
- Some more fiddling with the airscrews and it's now sounding nice and crisp. There's a little bit of hesitation here and there when I roll on the throttle from about 1/4 ish open, but I can sort the needle and main jetting next weekend.
 
No updates, but I've still got it and riding it regularly. The riding weather is too good at the moment to be working on bikes.
 
Hey just made a account but, is it worth getting a nsr250 mc16 for $3900 aud with about 19xxxkm on the clock looks in nearly perfic codition and I have about a week to decide if I want it or not
 
You must log in or register to reply here.

DTT Light or Dark

  • DTT Light
    • www.jadusmotorcycleparts.com
    www.lostapostle.ca/
    www.sparckmoto.com

    Spread the Love

    Back
    Top Bottom