Starting with the throttle, let’s first take a look at the servo. There are those pilots who believe the throttle servo should be just as fast and powerful as those used on the swashplate so rapid throttle changes can be made for 3D flying. However, I am not of this belief for the following reasons. First, the throttle on the engine requires very little force to move from idle to full power, negating any requirement for a powerful servo. And, since all helicopters require a high-power setting for even normal flight, the throttle barrel is always open to at least 70-percent power. This means the throttle barrel only has to open another 30 percent to sustain any type of maneuvering. The advantages of a fast servo are therefore lost because of the small movement required. This is not to say you can’t use a more expensive servo on the throttle, but rather that it is just not required.
Most carburetor control arms have more than one mounting location for the throttle pushrod. I recommend mounting the pushrod to the longest arm possible because this will give you the finest control possible of the carburetor. This is not important at high-power settings but is very beneficial at idle, where one or two clicks on the throttle trim will give you that perfect idle. Then mount the pushrod to the servo, bring the throttle trim to full idle, and hold the pushrod to the throttle servo arm at both full idle and full throttle. With a little experimentation, you will find the proper location for the throttle push-rod on the servo arm. If necessary, use throttle sub trim to make minor adjustments. Using this technique, the throttle barrel will be full open at full throttle, fully enclosed at idle and idle trim, and the engine should idle nicely when the trim is in the mid-range position.