I just got an MC18...

I have a similar problem...

I have a stock MC18
standard jets.
tyga pipes.
open airbox.
no-battery.
running 93 octane super unleaded...
and just some regular two-stroke oil...
standard plugs NGK BRE8 or what ever...forgot...

I kickstart it it starts fine...

I ride around town, it rides fine..

Accelerate with POWER holding the throtle cracked at 1/2 to
3/4 it hits the power band around 9k-10k.

cool...

but I get on the highway...
accelerate up to about 100kph-120kph
and hold it in 6th gear...for about a mile...
and one piston seems to go dead...

get off at the exit...and whil idling the piston starts firing again...
I think that it is the top piston....

is it fuel starvation?

I checked the carbs...took them out...check the floats, jets....
emaculately clean...

the bike was aquired by a collector before I had it...
sopposedly...the whole bike looks in really good shape...
I think he restored it.....

I held the tank up...turned the fuel cock and fuel just flowed out...
so I don't think it is the tank...

but tomorrow I will dain the tank an remove the petcock..

I will also install a battery...

someone said up there, that some guy had that same problem
and it was that he had no battery....

-cheers..