I did a lot of playing around with the LA 40 using the stock RC carburetor. It makes a handy variable venturi. The 40's seem to want to run best around 1/2-2/3 open. If the throttle is closed too much you just don't get much power. Wide open makes plenty of power, but the handling gets erratic. They also seem to want to run, fully leaned out, at around 11,500-11,800 rpm. I find that if the venturi won't let it turn the prop at least that rpm, leaned out, the motor doesn't behave very well.