Quickie engines (Jett and Nelson) do not have carbs like a normal RC engine. They have air valves used to shut down the engine at the end of the run. You tune the engine with the valve wide open (down 500-800 rpm from peak). However, you can "throttle down" by closing the air valve somewhat. The mixture will go rich, and the engine will drop down off the pipe and run at about half power. Launch it there, then open the air valve and hold on...........