If the throttles work smoothly, very little effort is required. I just finished building a Sig Kadet Senior twin engine model that has OS FS .40 Surpass 4 stroke engines on. I used seperate throttle servos in each engine nacelle. The servos were only 17.5 oz.in. torque. These are very light servos, so the there was a great weight savings over a standard servo.

Whatever you use, make sure the carb barrel rotates easy and smooth and no linkage binding.

Rod,