P210 Help needed

Hi, Im running in a 210 malossi setup.  Included is, malossi head, piston, barrel. 30mm delorto with 40 slide, X7 needle 2nd clip, AV264 atomiser, 70 choke, 55 pilot, 250 float needle valve, finished with a 130 main.  Mazzecheli race crank, casings matched, lightened flywheel, and the JL SIP EVO exhaust.  There has been 170 miles done on the motor so far.  I was running at no more than 50mph until yesterday when I decided to take it a little further.  The issue then came up that it pulls like a train in 1st and 2nd, but change into 3rd and it drops right off, with no pull, almost as if the motor is trying to shut down. Can anyone offer suggestions as to what might be wrong please.

Have you spoken to the PM tuning guys I found them realy helpfull.

so, a friend of mine took the bike for a few days and adjusted the timing, and rerouted and shortened the fuel pipe.  It now goes off the clock.  I have been advised to increase mainjet size and float valve needle size to ensure fuel is sorted through the entire rev range.  Im now saving for brakes.  My retro gola shoes have no soles, and I had to throw out a pair of pants....

Just a thought but are you getting enough fuel through have you fitted a fast flow fuel tap.

thanks for the reply.  I was hoping someone from SIP would read this, and reply.  As I'm hearing different solutions.  But the most popular one seems to be that the exhaust may be the problem....

It was me that posted the above reply not Andy B. I have no idea why Andy B 's name is linked to it.

there isnt a fast flow fitted mate.  Before the engine went south it was running an old and battered PM pipe, 28 mil spaco, and a PM/piaggio head.  It was lethal with this setup.  

help still needed!!!