Hi there guys - i recently purchased an mc16 as my first ever restoration project - ambitious, i know i've been having quite a few issues which i'd like to get some clarity on.

shes an ex track bike, been pushed hard with around 35000 on the clock. ive replaced the battery and spark plugs, as well as some other odds and ends. will do more as time and money permits, but a few days ago i was riding on an uphill when the engine suddenly died - nearly wiped out completely. Seems like she was overheating, but there was plenty water in the radiator and coolant tank - had only been riding for a short while. she then would start and die if taken over 5000 odd revs - seemed to be running on only one cylinder. i got her home and looked her over - the plugs are fine, so are the battery and coils. she now starts first kick but only revs to about 6000, still feels like only one cylinder. Any suggestions as to what the problems may be and how to rectify them? i'm a complete newbie at this so any details would be greatly appreciated, thanks.

It is a bit difficult to know where to start.

I guess if that was my bike with those symptoms, the first thing that I would do is pull the exhaust pipes off and have a look up the exhaust ports at the pistons and bores. If the pistons have significant vertical scoring marks, then you have probably suffered a partial seizure. [ possibly due to a faulty thermostat?? or waterpump?? or 2T oil pump?? or fuel mixture too lean for whatever reason?? ]
I would also pull the carbs apart to check that it is running standard jetting. And if not, then think about why not.

Ditto - check your carbs ,does it have an airbox ? Clean the carbs and check the voltage on the battery , it must be above 12v 12.5 is good . Does the temp gauge work ?
When the bike is running open the rad cap and look at the coolant to see if it is flowing . Then you will know you pump is working .

Hi guys thank you very much for your prompt responses. The bike doesnt currently have an airbox - i think it was removed for racing- is it worth getting one? its not the waterpump i dont think - filled her up, rocked the bike and you can see the level drop when running.

TuckerBag so i just remove the 4-6 allen key bolts on the silencers and look up toward the engine? i forgot to mention this but another weird thing is that the bikes pipes arent smoking white like theyre supposed to.

Neal, the battery is okay thankfully - the temp gauge is, well, temperamental.

I'll take off the silencers today and let you guys know what i find, hopefully with pics. the carbs i may have to wait a day or two until i feel i've read enough to not screw it up. i found these two posts which should be fine as guides, right?

http://www.nsr250.net/forums/viewtopic.php?p=53423&sid=d31ce889c683b7c67ec0dceebe8d0a9a

http://www.nsr-world.com/tuning/250-tuning/carburation-index/jetting/

Thanks again

Ah,... where the exhaust pipe joins the barrel there are two M8 nuts (per cylinder) holding the exhaust pipe onto the barrel. (14mm? socket required)
You need to remove the entire exhaust system. You can leave the mufflers (end cans) attached to the main pipe (expansion chamber).

Feel free to make full use of the Parts Manual on NSR-World.

Then with the spark plugs out (and gearbox in neutral) it is easy to turn the engine over by hand (using the kick starter) while you look up the exhaust port of the barrels, perhaps with the aid of a torch.
When the piston comes up you will be able to see the condition of the piston skirt. Well part of it.
When the piston goes down you will be able to see the condition of the bore. Again, part of it.

That is usually a good enough inspection when checking for a partial or full seizure.
And yes, this involves lying on the ground with the back of your head hitting the rear of the front tyre as you peer up the exhaust ports,.. kinda thing.
Kick starter in one hand, torch in the other, whilst operating a digital camera in your mouth. Standard 2-stroke maintenance check 1(a).

Oh, and if you have a reasonably strong grip ( I can see the jokes coming already ) you can rotate the powervalve motor pulley by hand (with the ignition key off) to raise the powervalves to get a better look up the exhaust ports.
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[color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...

Ok,so first of all,I'm in port elizabeth sa,also bought a mc16,did a clean up,repaint job onit,38000km on clock,never opened up motor,3rd owner,I experiences the same single cylinder problem as you have,took me a lot of time to determine the problem,which was faulty cdi unit(it takes 2,1 per cylinder)the way to tese is to swop the cdis around and see if the other pipe smokes/fires,you'll emediatly see that only one pipe smokes if it runs on one cyl.I bought a 2nd hand cdi in jhb for r500 and problem solved.other places is r1500 plus vat,ns 2stroke etc.any help or assistance,please contact me,074 606 1122 johan

Okay, an update - seems to be heading downhill. Couldnt get the bike to start - checked, cleaned and sanded the plugs (mixture is a little rich), kicked her over again, still nothing.

Figured i may as well check the other stuff, so i acted on your advice. double checked the battery - 12.6 V, fine.

TuckerBag - did exactly as you said - i couldnt see anything (even with the torch) that looked out of place - moreover, while getting a mate to crank the kickstarter while i took a look the movements were smooth, so i think thats a good thing.

i have no idea what the powervalve motor pulley is - will give that a try once ive done my research.

the bike really needs to be fully stripped and cleaned, but ive just moved houses and dont have access to a truck or trailer. i really need to get her a) started and b) running for 15 mins so i can actually start taking it apart properly. im fairly orderly and confident in my ability to reassemble properly, even without a service manual (im a uni student, 90 dollars is way too much for me).

Any ideas and solutions as to the starting problem as well?
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oh, and one other thing. the choke cable is disconnected, and i have no idea where its supposed to be connected internally.
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There is no 'have to', only consequences. Accept them and be free.

If the plugs are sparking then it is a fuel issue , have you tried to push start it ? Get some carb spay ( quick start ) and spray it into the carbs with the throttle open .
If it fires up and dies aferwards you can be sure it is a fuel issue . Get an airbox or some pod filters to stop dirt getting into your motor .
If there is no spark when you kick it over then you need to check the main fuses and the kill switch . Hold the plugs in your hands while your friend kicks the bike - you will find out if they are working or not !

OK, so hopefully we can rule out a partial seizure. That's good news.
Looks like 2stroke maniac has probably got the necessary experience on this one.

ypanchia wrote:
i have no idea what the powervalve motor pulley is - will give that a try once ive done my research.

At the top of item 6, the power valve servo motor, under the tank. Just follow the cables up from the side of the barrels.

ypanchia wrote:
im a uni student, 90 dollars is way too much for me).

Just want to make sure you are aware of the free online parts manual.
Click here and drill down to your specific Model --> SubAssembly.

Choke cable connects to the top of the right hand carby, well I'm not 100% sure that is true for MC16?
In the free online parts manual, see "1987": --> microfiche "Carburettor E14" - part 24, and microfiche "Control Cable F3" - part 3.

If your problem does end up being a faulty MC16 CDI, then you will want to have a read of this thread on how to repair them.

Also, I can't help but think that the problem here could just be a build up of crap in the carby float bowls, resulting in blocked jets?
Simply cleaning out the carbies could be the fix?
Also check that your tank is not rusty inside. If it is then an inline filter in the fuel line from tank to carbies is highly recommended. A filter costs about as much as a Big Mac.
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[color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...

ypanchia wrote:From a different thread: How full is your tank? whenever i fill mine up a bit of fuel comes out of the two bronze pipes at the rear of the carbs - its not a big deal - as far as i know its just the overflow. i sorted it by closing the petcock ever so slightly.

This indicates that the needle valves in the carbies are not sealing properly.(or possibly the float level is set way out)
This will affect the float levels, and have a serious impact on how well the bike runs.
Possibly,the amount the needle valves leak differs with revs, (vibration frequency) giving you a varying float level?
You say that it won't rev past 6000rpm, this may be because at that frequency the needle valve leaks a lot of petrol and the float level rises to the point of overflow? Maybe not.

Anyway, I would fix this problem first and then see how the bike runs.
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[color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...

Hey guys, sorry for thr delay - been moving house so i've been a little distraced. Firstly 'd just like to thank you all for being patient with a newbie and taking the time to reply.

TuckerBag, thank you for the direction to the manual, i have had a look and its damn useful - keeping it open on my laptop while i work on the bike from now . i think the pistons are fine. i've got an inline fuel filter so i dont think its the rust - it could be the carbies - i disconnected the cables and oil pump line, then tried to take them off, and its impossible! one of the 4 bolts comes out, but the other three are stuck fast. i sprayed them down with lubricant and im going to give them a go tomorrow. Any ideas for getting them out if that doesnt work?

As for now, im going to head down and check the CDI's .

Thanks again guys.

That's a slightly worrying post!

Check you have identified the correct parts to undo! The carbs are secured to the manifold with two circular clamps [item# 6]...



As you can see from this diagram too, there are 8 bolts that secure the manifolds to the crankcase, not four. Be careful loosening and tightening the manifold, as it can easily warp, and that's not something you can see by eye.
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If you are taking the carbs off you may as well open them up to inspect the jets . The pilot jet is the small one and it can get blocked very easily .
Let us know how you are getting on .

EDIT - it allmost sounds like you are loosening the inlet manifolds , look at the carbs where they slip into the rubber , you should see a black steel clamp , look for the star screw to loosen it . It is normally at a angle so that you can get access to it from under the frame spar

Okay, as you guys said, it was the manifold bolts i was going for thanks Andy for correcting me - the carbs came off easy after that

i'm gonna do some reading and look through the parts manual so i can identify and understand how it works - then use this post http://www.nsr250.net/forums/viewtopic.php?p=53423 to clean them.

i have a feeling im going to have lots of questions soon wish me luck!
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There is no 'have to', only consequences. Accept them and be free.