Guys, having an issue with a MC16.

Bike starts fine and idles great. Once warm I took it for a spin but under load the tacho drops back to zero and then comes back again.

I parked it and it went back to idling fine, but then it seems like one cylinder kept dropping out and coming back, and everytime the cylinder would drop out the tacho would drop back to zero. Is the tacho dropping to zero a diagnostic?

Thanks in advance.

Hi,

If you read some of my previous posts I had the exact same problem with my MC16. I resolved it by replacing one of the CDI units with a brand new item from Japan.

http://www.nsr250.net/forums/viewtopic.php?t=6434&highlight=

Thanks for that, I read that post earlier.

I had issues with the CDI unit when I bought the bike, and replaced it. Since then it has run fine. Just seems to do this sometimes. What numbers do your CDI units have on them? Mine are C1530 and C1530A. Is the C1530A for a particular cylinder? Are they both supposed to be the same number?

Regards,
Jerry

Sorry don't have the numbers to hand but I know that swapping 2 working units over is absolutely fine so either will do.

I will give it a go. I have 4 CDI units to muck around with.

One question. If a cylinder is not firing because of the CDI unit is it still getting the oil from the oil pump?

Yes this is controlled by the throttle.

One thing to bare in mind if you are gonna dremel one apart is that you dont need to remove the potting! I simply dremeled the back (non connector side) off the unit to get to the back of the PCB and re-soldered any dry/dodgy connections.

I have changed the CDI units and still same issue. When I disconnect the rear cylinder the tacho works fine. So when the engine is only running on the front cylinder the tacho works fine, and the engine runs well on the one cylinder. Is this what happened to you? I am thinking maybe its a coil issue, would that be possible?

I found that at times the problem would disappear altogether and the bike would run fine. This lured me into a false sense of security, I'd go out on the bike and then it would drop a cylinder and the tacho would go insane. Changing the CDI's moved the problem to the other cylinder.

You could have a coil problem but if you look at the wiring diagram in detail it becomes obvious that the coils couldn't affect the tacho in that way. Maybe you have a combination of problems, best thing to do is sectionalise one component at a time.

Also check wiring remember you are working on an old bike which unless you bought it new you do not know the history of. I work in electronics and the simplest of things has caused me no end of problems.

Turns out it was a dodgy spark plug.

Great news !

Always comes back to the basics, my MC16 would eat a couple sets of plugs a year.

Jim