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The “twin spark” arrangement is much favoured by Alfa Romeo for a number of reasons. The main one (as I understand it) is that the combustion flame doesn’t need to travel such a long way from the plug, which means you can run

• more compression and
• more ignition advance and hence
• get more power

on low-octane fuel. So it’s a good thing. That’s the theory, anyway…

On FWD Alfa’s, the twin spark arrangement looks neater, because there is a distributor at each end of the camshaft. On a 75, there’s no room at the back because the engine is positioned as far back as it will go. Hence the dizzy on the left.

Apart from having two of everything, the ignition system is reasonably straightforward. The ignition timing is handled by the Motronic – you don’t need to adjust anything in the distributors. Just keep well clear of the HT leads when the engine is running – the system packs a hell of a punch!

If you suspect the ignition isn’t right, the first thing to do is to check that both systems are working. Try the engine with each coil disconnected in turn. It should idle normally.

The OEM plugs aren’t cheap (Lodge 2HL) but they work well.
Don’t forget to check the rotor arms and distributor caps – they are well hidden behind annoying plastic covers. Change ‘em if there’s any sign of wear. Strangely, the front rotor arm was GLUED to the distributor shaft on my car. I had to destroy the rotor arm to remove it (it needed replacing anyway…).

Some pointers if things go wrong:

• Firing order is 1-3-4-2
• The distributors rotate clockwise
• The rotor arms are resistive! Mine measures about 6000 ohms from centre to edge. This is probably to prevent the huge HT from wearing the plugs out too quickly.

A faulty ECU can cause ignition woes, but thankfully this kind of thing is pretty rare…