well i expected a personal attack and my problem with mine was a clunk line came off and with kid he knows not to come on the flight line and he could not hear me and if it hurt him have a look he had 3 jackets 2 x pants he had more protection than a swat officer . think if he ran straight into the prop a kick upthe bum is least of his worries .

now your problem 1/2 throtle to 3/4 throttle is a mixture problem not air flow maybe a needle dirty or wrong settings why do u think its the dirafram you are better off putting a bandaid on the hole if you think its airflow heres a test put your plane in position holding it in the move like knifeedge and try and recrate it on the ground .
you can ask any walbro mechanic they do have faulty carbis here mine has a forty gallon drum full off them
why do u think i posted this it is because i went down this track in the end i paid for a small engine mechanic with a walbro autherised mechanic as there were 2 planes exactly the same one mine one a freind we baught them togeather same mounting same cowel cut same most except servos his was doing what yours are doing mine is fine the mechanic said its the carbi straight away i was didnt believe him so we bolted his engine on mine . guess what it did the same thing so the problem followed he removed the dirafram from my mates engine and cheacked the pop off pressure and then looked at mine the pop off pressure was different so he made my mates pop off pressure the same as mine by changing springs altering the pop off pressure now no problems so thats where my theory is from fix the main problem not bandaid the surface .
well i know u dont beleieve me go to a small engin mechanic and see what he says .