I’m normally a whizz at electrics but I’m baffled at the moment I am running a standard 240Z set up with a 12v coil and ballast resistor. It was running beautiful and starting first turn until I changed a plug lead to check something and now it runs like a dog at idle despite swapping back to the original lead. Once off idle - no problem, revs and runs as sweet as. I decided it must be something else that I disturbed by accident or just pure coincidence. So I’ve swapped the distributor cap, plug leads and coil lead in turn, coil, ballast resistor, reset the points cleaned everything in sight. Still no joy. One thing I’m confused with is the ballast resistor circuit. If I have this right. the coil gets 12v for starting (from ignition switch start pos) and then drops down to 6v to protect the points, through the resistor. This is wired using a common line through the tacho, with the constant 12v power supplied when the ignition is turned on running through the resistor (down to 6v) and the temporary 12v start power supplying the main coil +ve.
When I turn on the ignition and check voltage it’s 12v at one side of the resistor, 6 at the other and 6 at the coil. So far so as expected. When I crank it the voltage at the coil goes up to 12v (again, expected) but when I check the voltages when running I get 12.6 at the resistor input, 10.5 at the output and around the same at the coil. So yes it’s gone down a bit, but nowhere near the 6 I expected. I have tried 3 different resistors but all give the same result. I may try taking the resistor output direct to the coil instead of routing it back up to the tacho and back down the to the coil via the common line. That might help but wouldn’t really explain the lack of voltage drop. Any thoughts or similar experiences. I know I’m probably one of a very small minority in here still on a standard points / carb setup but hopefully…
If I can’t sort it, it’s off to Bogg Brothers at Malton and hope that Dave is still alive to work his “old school” magic
When I turn on the ignition and check voltage it’s 12v at one side of the resistor, 6 at the other and 6 at the coil. So far so as expected. When I crank it the voltage at the coil goes up to 12v (again, expected) but when I check the voltages when running I get 12.6 at the resistor input, 10.5 at the output and around the same at the coil. So yes it’s gone down a bit, but nowhere near the 6 I expected. I have tried 3 different resistors but all give the same result. I may try taking the resistor output direct to the coil instead of routing it back up to the tacho and back down the to the coil via the common line. That might help but wouldn’t really explain the lack of voltage drop. Any thoughts or similar experiences. I know I’m probably one of a very small minority in here still on a standard points / carb setup but hopefully…
If I can’t sort it, it’s off to Bogg Brothers at Malton and hope that Dave is still alive to work his “old school” magic