I’m having trouble getting my MC21 to run well. It was off the road for years, and has not run well since then.
Compression is ok, new airbox seals fitted, all the usual things have been checked / replaced. Power valve is fine.

It starts on the first kick and will rev out perfectly on the side stand. On the road its not running well at all

Initially it was reving up to about 7-8 pretty weakly [there was a small bit of power there] It would run badly above these revs and would not rev any higher.

Carbs were properly cleaned several more times and set up to correct spec.

Now in lower gears it sometimes pulls reasonable well at higher revs, but the next minute it runs badly again. When its hot it gets worse and the choke makes no difference to hot running.

The rest of the time it runs badly.

Any ideas what the problem is?

Is there any way I can test the PGM? I would like to exclude it from the potential problems list.

Thanks

Spec -

It an R but has an SP engine, nothing other than the engines was swapped over. I cant see this being the problem as I ran it for years with this configuration and it ran fine.

Its got the wire spice de-restriction.

Is your battery 100% fully charged and holding charge at 12 + volts ? Put new fuel , new plugs , new battery and it must run .

new battery, plugs, fuel. it does run, just very badly

Powervalves checked for carbon build up?
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

the powervalves are in good order. i think it must be something electrical, likely small and hard to find. i'd still like to discount the PGM though

I am finding my engine hard to rev correctly above 9-10k although the symptoms are not as bad as what you describe. Just found that the ht lead was not correctly fitted to the spark plug cap. In my case, the coils seem to be OK but do measure their resistance and check them for cracks or bad connectors.
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Does it run smoothly up to 7k?

Does it run for short bursts then hold back

If so, it could be fuelling, even as simple as float heights set too low
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Why do things simply when you can complicate them

all the above and more checked again, still no joy. thankfully going to tokyo in a couple of weeks with work so will be bringing a pgm and new carbs back in my luggage. it has to be one of the two thats playing up.

thanks for the help. this war is not over....the beast will run again, or worst i'll have a spare pgm & carbs to sell!

I had a simmilar problem to this with an older 2 stroke bike, checked everything, couldnt find a thing wrong. Till I closly inspected the Reeds.
There was a couple hairline cracks in them, I replaced both reeds & Problem was solved.
Might wanna check your reeds mate, look inside & out. That will be one more thing to eliminate, hopefully it will fix it for ya.

You say you have cleaned the carbs out a few times, but I can't resist saying that it might possibly be that the needle valves have "gunked up" a bit after sitting for so long, and now are not working optimally with the floats?? Just a thought.
I would try a bit of Brasso on the end of a cotton bud to clean the needle valve seats.
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[color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...

Could it be the TPS? Maybe its come loose or needs fine tuning.

When the TPS was setup incorrectly on my 28 I experienced similar problems.