Does anyone have a rough idea of what size opening of the throttle is a good starting point for a decent idle? I just changed the servo setup and linkage completely and forgot to look at how it was before.

Adjust your throttle servo travel (ATV) so that the carb closes all the way with the trim all the way down then open it up gradually until you get an idle around 2200 or less rpm. Do the same thing on the high end. Increase your servo travel until the carb is fully open. Once the carb is fully open you should get a rpm of 8200 or more with a 18x10 apc prop. You may have to adjust the sub-trim as well.

Thanks, but I meant setting up on the workbench - like in mm, whats a good starting point for a barrel opening at idle?

Not sure of an actual distance, but it will idle with a VERY small opening.

Arch

Just what I needed, thanks! I'm trying to get the best possible symmetry in the setup so that I can have a good starting point for linear throttle without adjusting too much on the curve. Like if the idle position (starting point at least) is at 80% travel in one direction I like to set up the servo control horn so that the full throttle position is as close to 80% travel in the other direction as I can get it.

While I tend to be very fussy about linkage geometry for control surfaces and can spend ages adjusting pushrod lengths and subtrims to get equal surface deflection each way with equal servo endpoint settings, I don't worry too much over the endpoint numbers when it comes to the throttle.

However, I do tend to set up the geometry to give me improved position accuracy in at idle ie. throttle arm has only rotated past being 90deg to the pushrod by a little amount and the servo is about 60deg past "centre". This means a lot of servo movement for a little pushrod displacement (increased resolution) and the engine can thrash around as much as it wants as changes to the throttle barrel position due to engine movement is minimised.

A multi point line curve then gets the throttle to feel right. I also have flight idle set with the trim lever in it's middle position and the volume of the lever set to kill the engine on the landing roll out. I just can't get the hang of using a digital trim buttons for throttle....

Given I used to fly with a throttle ratchet that had about 20 something clicks (I now fly smooth as per heli's) I don't think that trying to maintain good servo resolution at anywhere other than the idle position is of any benefit.