As Truckracer said, proper attention to cooling airflow is essential. And as Lifer said, I just vent all my carbs into the fuselage as a matter of course. I would rather just do that while I am building/setting up the plane, than to perhaps find out that I need to and have to go back and do it later.

Then, just as Speedracentrixie said, you have to do your final tuning based on how the engine acts in the air. It seems there is always at least a little tweaking that needs done on the needles based on how the engine acts in the air, even with the regulator vent installed. The engine is loaded completely differently in the air than it is on the ground, and loading makes a difference in how a two stroke needs tuned.

Lastly, if you are still have troubles with a mid throttle burble, try increasing the propellor size/load. A too small propeller will often cause an engine to run ok static on the ground, but will then go rich and burble in flight due to the propeller unloading.

AV8TOR