Rev Counter Problem And Misfire

[joelpsmith 1]

My rev counter started going a bit crazy, when it goes over 4000 rpm it starts to jump around between 4000 - 8000.

I have left it like this for a couple of weeks as it was otherwise running fine, but it has now started to misfire which coincedes with the rev counter problem.

 

I've done a search which revealed either coil or ignition amp, i think. Although i'm slightly confused as to what the two of these do and which one of them is the problem.

[brianthemagical 1]

assuming it's an xu with a dizzy. use a ohm meter to cheack the coil. put the meter between the two terminals and cheack the reading. the primary terminals are LT + to -, there are two sets. the secondary are LT to the HT lead terminal. the readings should be: primary 0.8 ohms, secondary 6.5 K ohms. that all came staght out of my hayns manual. hope it helps. i'm not sure how to test the amps, suppose substitution is the simpleist.