Hi Guys, I have G-45's on my Ziroli DC-3 and I could tune for a smooth rpm all the way thru the rpm range on the ground, but at 1/2 throttle in the air, the prop was unloading so much that the engines would really go rich and 4 stroke big time. Raising the popoff did'nt really help, so I angle cut the black plastic velocity stacks that came with the engines at 15 degrees forcing the air into the motor and that really helped lean the mixure at 1/2 throttle in the air, cleaning up that 4 stroking. Tuning on the ground with a load on the prop, the engine requires more fuel at 1/2 throttle than in the air at 1/2 throttle. At 6o mph, there is not enough prop load on the engine at 1/2 throttle to burn the amount of fuel entering the engine, thus you get 4 stroking. That carb hangs all the way out into the wind on that DC-3. The angle cut forces slightly more air in the carb, thus leaning the mixure. Hope this helps Rick Simmons