I just went through this . I messed with pumps , head shims , plugs , tapering low end needle , closing one exhaust tube , larger fuel line , different fuels , 4 different carbs , and different combos of these .

I finally got it to run great today after alot of tinkering . I wound up using a Magnum carb off of a 1.08 . I made two head shims to use until the ones i ordered get here . I am running an O.S. F four stroke plug and a mix of 5% nitro and 18% oil with a 50/50 mix of synthetic and castor .
I am using the Bisson pitts style muffler .

I broke the engine in on the test stand with two gallons of 20% oil and burned another 3 gallons of 18% oil since trying to get it to transition well .

My idle and top end was great with all four carbs but the Magnum was the only one that would transition through mid range with out it looking like i was running smoke . Now it transitions clean and i can hover lower to the ground with out worring too much .

Barry