I installed an optical kill switch on a Fugi 63 engine which caused the engine to run roughly. While running, the LED in the switch circuit would flicker. The switch would promptly shut down the engine. After removing the switch the engine ran fine. It was replaced and removed several times to confirm that it was the cause of the problem. The switch was purchased from a highly reliable giant scale supplier. The installation is very straight forward. Is there a preferred brand of switch or may this be related to this particular engine?