Having a few electrical issues on the Speedster. Port tach reads above 4000 RPM but not below. I swapped the tach input with the starboard engine and the port tach reads properly. I'm guessing it a signal problem. Looking at the wiring diagram I see a 20k resistor in the line that comes directly off the mag. Could the resistor be faulty? I get good readings above 4k rpm. I'm going to check the mag plug to make sure I'm getting good contact. Help is appreciated.