The servo brand is not the problem. If you have good connections throughout the installation, no metal to metal rattles from loose connections and loose nuts and bolts, and the ignition/magneto is properly installed then there should not be a problem with any type or maker of servo. First check to see that a resistor plug was used on the engine. This can usually be determined by an "R" in the plug numerical designator. Next go back through the instructions that came with the engine and see if the installation was properly performed. I'm betting that something may have been overlooked in the installation process. Tape the crystal into the receiver opening to prevent it from being shaken loose or fractured by engine vibration. Protect the receiver from vibration better than you would with a glow engine.

Don't fly the plane until you can get 150 feet of range test or better with the engine running. A good installation will often provide a range test with the engine running the same as with the engine off. In any case there should not be more than a 10% difference between the two checks.