This has been an issue on my mind me ever since I started my first gas engine up last Saturday. The throttle response was weird! I've been doing a little research, and found this extract from Troy Built Models that summarizes the problem perfectly:-

"The carburetors on gas engines are not linear at all. At 1/2 open, they are at 85% power, and little happens between 1/2 open and fully open."

In my inexperienced words, there's an abrupt jump in rpms at a certain point (it went from about 4000 to about 6000 in about 2 clicks) as I open up the throttle and at others, there's barely any increase at all - I'm guessing this would make aerobatics pretty hard to fly.

So how do I program the throttle curve on my transmitter to smoothen out the response? I'm thinking:

#1 Identify the point at which the surge occurs (with a tacho) and then reduce the curve % at that point

#2 Increase the curve gradient where throttle response seems sluggish.

Thereafter, do I just click the throttle lever forward 1 click at a time and adjust for a uniform rpm increase?

What about expo? Should I turn it on?

Sorry, I've never felt the need to do a throttle curve on my glow aircraft engine and my only experience was a brief and passing encounter when I was setting up a heli. For info if needed, the engine is a brillelli 25GT and my transmitter is a JR 9303 equivalent (its marketed as a 9X2 here).

Will be very grateful for any help or suggestions. Thanks!

I have used expo on mine with great sucess. I put my stick at half throttle and adjust the expo to get the engine to run a little over half of max rpm. I use this as a starting point but it is usally close for me. This way I can fly and 3D my Extra with the stick mostly around the center. This with a DA 50 by the way. Works for me. Others use a point adjust to set 3 or 5 different rpms from idle to full bore. Use the functions in your radio to make the throttle react the way you want. The aircraft will be more fun to fly....

Thanks Cobra, that does sound like a more simple and straightforward approach. Will try it as a starting point and take it from there.