What's that on the side of the dizzy?

Magicdrshoon · Post by **Magicdrshoon** » Sun Oct 19, 2014 10:57 am

I know I'm being a bit dim here, but what's that thing on the side of the dizzy?

Is it normal for the king lead to have a resistance of between 6.5K and 7K ohms?

Is it normal for the ignition coil to get hot while trying (for a while) to start the engine (without success so far!)

Thanks for your help.

DaveEFI · Post by **DaveEFI** » Sun Oct 19, 2014 11:27 am

It's a capacitor. To help suppress RFI - radio frequency interference. Originally to help prevent ignition interference on the car radio - and to radios and TVs etc in the vicinity of the car - but also for any other electronics the car may use.

Plugs leads and the king lead usually have a resistance of so many ohms per unit of length. What you're looking for is one which is many times this - as happens when they burn out. 7K sounds about right.

The total between coil and plug is usually round about 20k including the carbon brush to the rotor arm. Obviously you can't measure this directly due to the air gap at the rotor arm.

ChrisJC · Post by **ChrisJC** » Sun Oct 19, 2014 7:51 pm

With reference to the coil getting hot, yes it does on a points car, no it doesn't on a transistorised ignition. It looks like you have a transistorised ignition, so I don't think it should get hot.......

Chris.

Denis247 · Post by **Denis247** » Sun Oct 19, 2014 8:53 pm

That looks like a system where the transistor is just an interface between the inductive pick-up and the coil, in which case the capacitor may form part of the ignition circuit, just as it does on a points system.

That capacitor looks pretty manky and, if leaking, could be allowing current to pass into the coil. I would replace this first.

It's only capacitor-discharge electronic systems, ones that just fire a (series of) high voltage (400v or so) but low-current pulse(s) into the coil, that won't cause it to heat up.