If you recall an advertisement for the "Snake Drive", well it is metallic which has potential to carry ignition/etc noise back to the throttle servo, and then to the receiver.

What I do is take the Dave Brown (DB) fiberglass pushrod kit and mount the throttle servo back with the receiver and batteries. I machined a piece of nylon that mounted on top of an Airtronics regular round servo wheel (3/4" wooden dowel would work as well). One end of a DB shaft would slide in to the nylon adapter and be captured by a 2-56 cross bolt (see diagram). After checking the length from servo wheel to firewall (actually, I run mine into the engine box, then the firewall) I cut the fiberglass shaft to length.

Now comes the fun part. Using a piece of 4-40 rod, a large wheelcollar, and various diameters of brass tubing, I fashioned a fitting so that one end of the 4-40 rod would attach to the DB shaft in the normal manner but the other end of the 4-40 rod had a receptacle for a short length of flexible speedometer cable. The wheel collar, was silver-soldered onto the brass tubing, then the unit is soldered to the 4-40 rod. The wheel collar has a longer setscrew and is what pinches the speedo cable. The picture is worth a thousand words here.

An appropriate length of speedo cable, some brass tubing, and the proper size 1/2" to ¾" long threaded rod (usually 4-40) which screws into the throttle shaft butterfly makes up the flexible portion of the throttle actuator. You remove the original hardware used to actuate the throttle, screw the speedo cable assembly to the shaft and secure with a lock nut and thread-locking compound. When you mount the engine, the speedo cable engages the receptacle mounted on the DB shaft as you mount the motor. Close the throttle trim on the radio, make sure the throttle butterfly is closed, and then tighten the wheel collar. One can disconnect the throttle return spring if there is concern it will fight the servo too much. Using throttle servo travel volume (programmable radios) you can tailor wide-open stick position to wide-open butterfly. BTW, initially, you may think it will not work because of the throttle shaft position, but maybe it might if the carb was rotated 180 degrees it would. Sounds like a lot of work, but it really is not. Refer to the diagram.

Advantages:

-the length of fiberglass shaft eliminates the RF connection

-direct drive, no servo linkage slop

-adjust once and forget

-linear response, the throttle butterfly rotates degree for degree to movement of the servo output shaft

-Using exponential, throttle stick position can be better tailored for a more linear or proportional feel for a given amount of stick movement