Regarding throttle/carb non-linearity.... another point to consider. The relationship of the take-off points at the servo and the carb arm. The DL's I've gotten have a fiber "arm" that can be installed on the carb, or (as I've done) modify the throttle butterfly shaft to take the blue aluminum arm that comes in Hitec servos that can't be used for real control surfaces. That makes the take off point on the carb to be roughly 5/8" from center.

Then, on the servo, use an arm of 3/4", and adjust it so that the arm is moving nearly straight during the idle and low throttle movements (for those not familiar, this is "mechanical expo and differential").

When setup this way, there is very good resolution and sensitivity of response from the engine at the very low stick movements (desired), while becoming somewhat "numb" toward the top 1/3rd of stick travel (also desired).

Then, apply the curve/mix from the TX features to fine tune.

For many, this will be way too much work, energy, time, and effort, and will require too much planning..... for those, you'll never be happy with the response of these engines and carbs. They simply are not linear at all, nor sensitive enough where we need them to be.