carbon brush melted in dizzy cap

[cnicholson]

I have a mk2 pre face lift pi, with a sports coil and uprated alternator (55 amp) the car has developed a misfire and dies when reved, I had a look at the points today and noticed the contact in the dizzy cap seems to be melting away? or breaking up, would this be the cause of the misfire and poor running? also what coil should i be using on this type of setup?

Any help welcome, at this rate I will be needing a boot full of spares for the RBRR

[Lord Sorbington]

If the carbon brush in the dizzy cap is defective it can cause a severe misfire.

I once mis-fitted a rotor arm to a Metro which damaged the carbon brush in the dizzy.  Press the rotor arm fully home, new dizzy cap, problem solved.

[Nick Jones]

What does the centre of the rotor arm, where the carbon brush makes contact, look like?  Should be smooth and shiny with a circular rub about 4 - 5mm in diameter.

As you've probably noticed, the carbon rod is spring loaded and should make good contact with the rotor arm.  If it's just making intermittent contact then the spark jumping will erode both the carbon and the rotor arm brass.

This could be because the carbon rod has become jammed or because it's worn right out.  Freeing it off if stuck or stretching the spring a little may solve the problem - for a while at least.  New cap and rotor arm might be a good move.  Strongly recommend a red Dizzy Doctor / Rarebits rotor arm as the black ones currently available are dire whatever box they appear in.

As an aside, both PI distributors that I've come into contact with in recent times have been utterly knackered with vast unwanted free-play in the central shaft and non-functioning mechanical advance, so a critical look at yours might not go amiss.

Cheers

Nick

[piman]

Hello Carl,

is the sports coil suitable for a ballast ignition system, or have you by passed the ballast?
Alec