Hi there I'm a new member from New Zealand. Bought a freshly imported MC21 NSR250R last year and have been loving riding it. Just recently took it for a decent ride, was running really well no problems at all. Then the other day I got it started and it was idling but would just die if you tried to rev it and didn't really sound like it was idling normally. I've checked the battery voltage and the wires running to the coil but it all seems fine. Any ideas on where else to look?

Cheers Joseph

Basic problem solving first. Check your spark on coils, condition of plugs, clean carbs...etc In the process you will get a chance to visually check condition of lots of other things.

From there you might get a better idea of what is wrong if that doesn't fix it.

I have decided to join and help Joe out because he is a lazy bastard and his bike isnt going to fix itself.

I compression tested both cylinders and they both read around 140psi which i thought was fine.
I pulled the carbs out and gave them a clean but they werent very dirty and the jets were clear.

When starting the bike the left cylinder takes a little longer to fire and when rev-ing the engine bogs down around 2000rpm, the rev gauge jumps around and the oil light flashes.

Im not familiar with NSRs (im a RGV owner) so i dont know where the rev gauge gets its signal from.

I didnt have a multimeter so wasnt able to check the battery under load.
My next plan will be swap the coils and plugs over and see if thats were the issue is.

Are there any common faults that give these symptoms? or other tips?

Thanks

Hey guys, ive just had that with mine
We tracked it down to dirty conections to the coils, we cleaned up the spade terminals and its all good
A common fault apparently and the rev counter jumping about means its loosing spark
Paul

The terminals didnt seem obviously corroded but i will run some sand paper over them just to be sure.

Thanks

Rather than clean them with sandpaper, use a good contact cleaner. The terminals have a fine plating on them the help resist corrosion (remember, even the newest NSRs are still 15 years old now, and the latest MC21 is 20 years old, and have often spent quite a lot of time exposed to the elements!) so scratching it off will only promote faster corrosion in the future.

Clean the terminals up and give them a little squeeze to tighten them up.

It sounds to me like it could be the reg/rec. You should put a volt meter across the battery and check the output on idle and throughout the rev range. It should remain constant at around about 14.2V.

There is a fault-finding chart in the Workshop section, and also numerous posts about checking the reg/rec and poor connections all over the forum across the last few years if you do a search.
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Ok thanks i will try that.
Is it possible its a bad earth? Do both coils use the same earth?

Had another look tonight.
Tested the battery:
12.7v bike not running.
At idle it dropped to 11.7v
When reved (3k rpm before bogging) it was anywhere from 12.7 to 13.7v
I put the battery in my bike and it was sitting at 13.7v (which is good in a rgv)
So I guess that suggest the rectifier.

Won't be doing any more work on it as it well over due for a top end rebuild