TR6 Electrical ignition problem

With a restoration of a 1972 TR6 just begun, I come across a problem ( one of many) that I can't isolate yet. It will run decently for a while then begin to misfire so badly that it is difficult to get it going more than 25 mph. An then...... It will run fine again. The usual have been done. New points, plugs, plug wires, coil and condenser. It has been timed and the carbs have been adjusted, not rebuilt yet but adjusted. The odd thing is that when it starts to misfire, I found that if the engine is turned off and on again the misfire will often stop immediately. Not every time but most times.

any ideas of the cause?

Forgive my ignorance but does a '72 TR6 use an electric or mechanical tach? If electric, what is the needle doing during the misfire periods?

I believe the tach runs off a cable. It seems to be accurate through the misfire occurrences.

Jimmy, run a wire from the + side of the battery to the + side of the coil. If the miss stops you have a ignition switch problem, or a bad wire in that system.

Wayne

Thanks Wayne, I'll give it a go

Wayne

Thank You!! It was surprising how much better it ran with the jumper in place and no misfire. Now for the unpleasant task and contortions trying to get under the dash and replace the wiring and switch. The car had been owned by someone......... Resourceful.

thanks again

Jim

If the jumper wire makes it run better you might also have an issue with the new coil you installed; I can't remember but ISTR that there is an inline resistor to the coil which lowers the voltage after the car starts, that may have gone bad, you could check what the voltage between the + side of the coil and Ground. check it with ignition on and engine stopped, then check it again while it is running (without the jumper cable attached)
If it has a resistor then the voltage will be less than 12v while the engine is running, if you installed the wrong coil ie one that expects and is designed to get the full 12v then that could be a source of the misfiring.

Just to answer with the final reason for the misfire. It was the carbs. One of floats was badly out of adjustment. Only 12mm from float to body instead of the required 16-17. Runs great now

Thanks for posting the solution! It can be frustrating to see many suggestions, but never know what actually fixed the problem.

Also interesting that your car ran better with that jumper wire, even tho' the problem was actually a carburetor float.

Thanks.
Tom M.

Somewhere in its history, the car had been re-wired. But they kept the 12 volt coil from the 1972 configuration and used a 73 or later wiring harness. The wire feeding the coil was a resistor wire and only fed the coil with 8.57 volts. So the jumper wire straight off the battery did make a big difference.