Hi all,

I'm new to the forum but have already found a lot of usefull information by searching through old threads.

Unfortunately I have a problem that's starting to drive me crazy... Please forgive me for what I feel could turn out to be a very long 1st post!

I bought a MC16 in Portsmouth last year. As I live in Denmark I had a rather long journey home...
I'm sure some of you know the bike already, it's an hybrid:
MC18 rear swingarm, MC21 front end, magtek rear wheel and what seems to be an MC16 FIII exhaust. And in a custom blue/silver paint job that I personaly find more seldom than good looking


At first it started just fine, tick over was somewhat rough... seemed a bit rich on the mix and would stop when put into gear if not reved some (and yes I'm familiar with reving 2-strokes during take off - but this was with the clutch fully engaged).
After 100 miles or so the bike started running rough (partly on one cylinder and won't rev up).
Got to my first destination and after turning the bike off it was really hard to start again. Surely only ran on one cylinder by now.
As I have earlier had an TZR with YPVS, and the feel was a bit like when the YPVS was stuck closed I checked the RC servo, cables and allignment, all looked good.
Got the spark plugs out and had no spark on one of them and it looked fouled (can't remember which though)
Replaced spark plug and it got me all the way home (approx. 500 miles). Though at the end it started to make the same rough running...

I then left it over winter and pretty much forgot about it.
Was convinced it was all down to a way to rich mixture so started last week by cleaning the carbs and checked all settings.
All jets are standard, MJ 110, SJ 35, float heigh 13mm, needles standard.
Air screw was 2 turns from fully in. Set this to 1½ turn as per specifications (though I understand this would give an even richer mixture).
Must admit I didn't have a new gasket set, so had to do with the old, but they don't seem to be leaking anyway.
Air filter was very oily so gave it a good clean. Airbox had been modified by drilling 4 holes in the top cover (pretty standard mod from what I understand).

Checked the wires for the coils, cleaned them and made sure the "plugs" was nice and tight.
Measured the resistance to 9.65-9.85 kOhm with the plug caps on (spot on from what I understand).

One thing that surprised me was the tiny ground wire on the bike, is this really standard? I cleaned the ground to frame connection (at the bracket for the upper cylinder coil). Measured resistance to approx. 0.3 Ohm from the battery.
Gave the battery an overnight charge and replaced the spark plugs (didn't look to good).

After this small "service" I haven't been able to start the bike up, so I'm now looking for any help that will point me towards my problem(s)?

I have spark when holding either plug to the cylinder head (though not sure how strong the spark should be), and one or both cylinder(s) it does fire very shortly.. But only when holding the throttle partly open.
Pulling the plugs shows that it's getting petrol okay, maybe it's even being flooded!

I will check compression tomorrow, must admit that I didn't think of this at first as the seller had a receipt for a top end rebuild from Stan Stephens less than 1000 miles ago. I don't have the paperwork with me at the moment, but if I remember correctly it also had new crankshaft seals.

Before I gave up tonight I cleaned the flywheel and pick-up coils but haven't tried to start it up since... Thought I would leave it overnight to let any excess fuel vapurise.

As I have spend quite a few hours trying to figure this out I have the following questions that I hope some of you could help answer:

1.
I get about 13.5 volt on the battery, dropping slowly when ignition is on. When trying to start around 12.8 volt. Is this okay or should I try to connect a backup battery?

2.
Bike was fitted with BR9ECM plugs (not specified for the MC16).
I know that BR is the resistor type spark plug, but will these put more strain on the ignition system?
I have now installed BR9ES plugs (B9ES was not availible of shelf at the local dealers).

3.
Plug caps are 5 kOhm resistor type, are these correct for the MC16?

4.
Should I try to install new float valves? Float height looked good, but the mixture sure seems to be very rich.

Next on my list is:
Compression test
Installing a battery that I know holds current
Better ground wire (negative battery connection)
Cleaning the exhaust
Cleaning the RC valves
New float valves
Checking all cables to/from the CDI

I'm still of the impression the mixture is to rich, but I'm not sure if it's possible that it's so bad it won't start at all?
I'm aware I adjusted the air screw by half a turn, could this be the reason it won't start?

Also what could cause the mixture to be that rich? Float valves that doesn't seal?
By the way I find the foam air filter to be very restrictive, and air gun can hardly blow air through, even now that I've cleaned it, is this normal?

Any thoughts are welcome, and thank you for a great forum with loads of great information...

Do your compression check before you make any assumptions. Take an old spark plug (known to be good) and snap off the ground electrode. Lay it against the head. If you cannot get a spark to jump from the center electrode to the threaded edge(about 4mm) at cranking speed it is unlikely to fire under compression. Keep us posted.

check you float valves aren't sticking! and clean the seats with brasso and a cotton bud in a power drill!

Thanks for the advice...

I now have good and bad news!

Good part is that I'm now convinced I have a good spark. Got a nice strong blue spark on both cylinders without the ground electrode

Next good thing is that I'm also pretty sure what the problem is.
I only have 90 PSI compression on the top cylinder, and it takes a good 5-7 kicks to get it up there! But turns out I only have 20-30 PSI on the front!!!

No wonder it won't start... I'm really happy I made it home to Denmark with that engine!

I will start taking the top end off now, but needless to say I'm expecting the worst.
That MC21 engine on Ebay from Cyprus is starting to look really attractive

Any thoughts on this? Would worn piston rings make this much difference, or will I see a piston that's destroyed?
I'll buy the nearest guesser a beer next time I'm in the UK or Australia

Could the engine have been runing very lean due to the HRC pipes (as upossed to what I thought)?
If the bike really had a top end rebuild less than 1000 miles ago I wouldn't expect this kind of compression unless something is seriously wrong!

/Valdemar

are you making sure that the throttle is opened when carrying out the compression test.

you will just have to open your engine up to see if it needs a new piston.

mc21 engine will not bolt into an mc16 and all electrics are different.

the engine was probably running very lean it should have been upjetted for the airbox mod and pipes.

if the engine was rebuilt it would not be good to run it in on such a long journey.

just get top end done and make sure oil pump is working and get the bike jetted accordingly.

Well front cylinder is off. Piston is gone, cylinder is also going in the bin!

If it ever had a rebuild it has not been very good... looks like the nicosil plating have come off in areas and even the head looks pretty bad!
Must have been very lean or not assemblied correct.
I know for a fact that the oil mix was good.

I'm aware that the MC21 engine won't fit, as the MC16 is mounted directly to the frame, but I will need at least one "new" cylinder and as far as I understand the cylinders will fit straight on the MC16 crankcase.

That will also be an performance upgrade I believe and already have a set of MC18 carbs to put on it.

I'm sure the engine was already bad when I picked it up, as I wrote tickover was not good and I had problems after no more than 30 miles.
Of course the damage are now much worse, but I had no other option than to drive it the 500 miles home...

I will be looking for spare cylinders (preferable MC18/MC21/MC28).

Will also go for premix and get rid of the oil pump!

Be aware that I'll be bidding on the MC21 engine on Ebay

My first NSR was set up for premix when I got it. Turned out to be a pain and over the winter I replaced the original oil pump items that luckily came with it. Converting to premix on a street bike doesn't do a whole lot for you except make fuel ups irritating!

Sorry it was a bad experience and I hope you get your engine sorted soon. Once you're back up and running it will all be worth it though especially if you reassemble it yourself.

Craig

Hi Craig,

Thanks for the support... I might have a 2nd thought about the premix then. Though I kind of like the idea of not having to worry about the oil pump.

I'll surely put it back together myself, are used to working on cars and bikes but not NSR's!
If I can't source a good cylinder at reasonable price I will have to break it though!

Seems like parts are very rare and expensive...

Some parts can be, but keep looking, you'll find most things eventually. It would be a shame to break the bike for the sake of one cylinder.

Middo,

I agree it would be a shame, but I can see that Moriwaki-man is looking for approx. 650£ for a replated used set.
Then I will need new pistons etc.

That is way more than I can justify spending...

Try not to break your bike for spares man, us mc16 owners need to keep them alive! there's not that many around in one piece!


The first thing on mine i had to sort out was the cylinders,mine were in a bad way, but i found some in the end, or you could get them repaired and replated might be cheaper.

Waldo good luck with your build, like others have said there aren't many MC16s around still running. Post pictures of the build if you can!

NSRs certainly aren't the kind of bike you can just buy and expect to go perfectly. It really is a case of trying to figure out what the previous owner did and what you need to do to make it run right. I'm still fiddling with mine trying to get the jetting and suspension set up just right but hey it's fun for me.

Cheers
Tom

Depending on the damage to the cylinder, I would just have it repaired. Repairing is a lot cheaper than buying used cylinders and the coatings these days are apparently way better than the original nikasil. My top cylinder was totally stuffed. Nikasil was a mess and had a number of cracks in the ports. I had them repaired and all is well (apart from my son dropping the bike and damaging the fairings).

Andy

Bandit7

yeah, i'd go for repairing the original cylinder and get a new piston etc. will save you a fortune, and you'll know you have a good cylinder, if you replace with a second hand cylinder you won't be sure of the condition!!!

Waldo, unless the previous owner altered the configuration from when I last saw it, I believe you have MC18 cylinders on that bike. Post a photo of the damage, and someone will identify it for you. They key to identification is a nice clear shot of the exhaust ports. MC16 ports are quite narrow/small, but the 18 looks like the map in this thread:

http://nsr250.net/forums/viewtopic.php?p=65898

Fitting MC16 or MC18 barrels is straightforward, but fitting MC21 or MC28 will also require their respective head(s) and altering the plumbing. Far from a difficult job, but it could be a bit of a pain.
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Andy.
NSR-WORLD.COM

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