Tach troubles? I think

Thanks to all your help my 80 is back on the road. After replacing the lines and calipers and then replacing another one again . And then the M/C I think I can safely say I have the cleanest Brake Fluid in South Florida. Took the carb off to get the secondaries to close up and found the PO had stripped the inlet. My plumber fixed that. So now she is just purring along until last night. Suddenly it feels like It's running on seven and the tach quits. Checked the filter wires and all looked ok. This morning I fire her up . Tach's fine and its running great. Drove it for a good hour to make sure it wasn,t a heat issue and it's fine. I don't know if its gobblins or does anyone have an idea what gives. If there is a wiring problem, I want to fix it before worse happens...

Thanks

It's possible that either the condenser in the ignition or the tach filter is shorting out when it gets hot. Not common but it happens. And yes, HEI does have a condenser.

where the wires connect to the HEI could be close to falling out one is the tach and one is the hot wire for the ignition