Well, guess what guys, the hole in the brass insert was exactly half blocked by the carb body! Seems like they didnt pay enough attention when assembling the carb and they probably passed it on doing an air flow check (blowing through the hole) which would not pick up the restriction. This 'anomaly' has GOT to restrict the high speed running fuel flow!

I drilled out the hole only with a 1.5mm drill using the inlet nipple as a drill guide. If I had not promised to leave the nipple alone (!!) to determine if the this one mod made a difference, I would have drilled the whole thing through with a 1.8mm drill. Watch out for breaking the drill bit, I had mine snap off inside as the hole completed and the drill fell to the back end of the brass insert. MAnaged to pick/flush it out phew! Cleaning is very easy blowing through with some wd40 using the plastic tube extension into the holes. Remove the barrel before drilling and remember to backflush from that side afterwards, then use a strong light one side to check all shavings removed. Use a smidge of locktite on the nipple threads, needle holder threads and barrel retaining screw on reassembly.

For y'all out there with suspicious running motors, this is such an easy check to do. Remove the fuel inlet nipple with a 5mm spanner, shine a light in the hole and it will become immediately obvious if the hole in the brass sleeve is in alighnment with the carb fuel inlet or not, a 2 minute check.

Will run and set up the motor this evening, may not pick up the motor cutting, but should be able to see the motor leaning reaction to nose up test and needle sensitivity. Test flight report will only be available monday unfort.