I friend gave me a 93 XP that hadn't run in about ten years. I redid the carbs, fixed the fuel tank and got it running. The tach doesn't work tho. after some basic continuity checks with my multimeter it seems the 20k ohm resistor is shot. What is the function of the resistor? I'm heading to radio shack for probably a 50 cent part, or can I run without it?