Hi everyone
I've got a problem which has me stuck so it would be great if someone could help. I brought a mc11 ns250r which needed a bit of work to get it back on the road, got it all done took it in and got a wof, (warrant of fitness, dont know what they are called in other places but im sure you get the idea) when i got the bike back it was only running on one cylinder so checked the plugs and they were both the wrong ones so I replaced them and it went well for a bout 3 days then started running on one cylinder again, so i took the boot of the spark plug and put it back on and it was fine again, did this a couple times to get home and then the next day i started it to see if i could work out what was wrong but only one cylinder again. since then i havnt been able to get it to run on 2 cylinders. so enough with the story. The things i have checked are: it is getting fuel/air, and it has compression and the other cylinder works fine. I shorted the spark plug lead slightly (to get rid of any corrosion) and re-screwed the end back in but this didnt help at all. The spark plug puts out no spark (have tried with one i know works as well) the lead will ark to the frame when its turned on but there is no spark plug on it. The other cylinder runs fine, but when the resistance is measured across the wires before the coil (with the coil un-pluged) the one that goes gets about 37killer ohms (i think, might be out by a magnitude of 10 or 100) and the one that dosent go, gets a reading of about 157killerohms (again may be out by the same order of magnitude) when the voltage is measured across the frame and the spark plug lead it measures about 0.96 volts.
Dose anyone have any ideas? or more tests I could do?
thanks for any help

Swap the coils and see if the other cylinder dies. Probably a duff coil. It wouldn't surprise me on a bike that old.
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Hi
I swapped the coils and the other cylinder dies, dose this mean the coil is buggered? I dont really understand how the ignition works but if it was fine wouldnt the cylinder not run anyway because it would be sparking at the wrong time? also I can only find generic honda coils in New Zealand, the description is "good working condition,suitable for all honda cdi type ignitions e.g. nsr250,nifty 50,xr 200/250/400/500/600" dose anyone know why these wouldnt work?
thanks again

o o


Last edited by DifferentStrokes on Mon Sep 28, 2009 9:56 pm; edited 1 time in total

Hi again everyone thanks for all your help
its not the coil.... i replaced the coil and it still isnt working. what do u think is the next thing to try? I broke my car at a track day an i think the bike looks cheaper to fix now so it is main priority lol.

Just a guess, but does the NS250R run two CDI's like the 1987 NSR250? If so, I'd suspect the corresponding CDI. See if you can swap them over if that's the case.
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what would the cdi's look like and where would they be? after the coils the wiring goes into the main harness and i cant follow them back

Hi again
I think i have checked the cdi's (if they are 2 rectangular boxes with 6 wires going into each?) and they both work on the top cylinder, so do the coils. I had smoke from the bottom exhaust briefly. Is it likely that this means that the other coil had died by chance at the same time as the cylinder rings or something have died and it needs a rebuild?

Have you checked or replaced the plug cap on the faulty cylinder?
I`m not sure on the MC11, usually the cap is a resistor type.
Can`t remember but, I think the resistor in the cap is around 5k-ohms? It usually tells you on the side of the cap. Stick a multi-meter across it. Obviously, if it`s open circuit, it needs replacing. The reading wants to be somewhere near 5K, depending on the temperature.
Give the plug a good clean or replace it also.

Hi
when i tested the coiles by swaping them over i swaped the caps over as well (are the caps are the bits that go on the top of the sparkplug to atatch them to the lead?) and they both ran the top cylinder.
thanks for your reply

The caps are the bits that scew on the end of the leads and push onto the top of the plugs.
The point is there should be a resistance value across the screw terminal and the terminal that pushes onto the plug. If you get an open circuit reading or very high resistance, then the ignition system will be loaded more heavily.
Broken/open circuit caps will still work as the spark can jump gaps, it reduces the spark at the plug though. It`s harder for a spark to jump across contacts that are under compression too, so you may get a spark when the plug is rested against the cylinder head. It might struggle when under compression in the cylinder though.