Hello all-
I have a 1972 500L with a 126 engine. Everything ran fine until last year, when the engine would develop a misfire which quickly got worse causing the car to stop. This would happen after about 20/30 mins. Fuel was being delivered to the carb, but there was no spark at the plugs. I have replaced plugs, HT leads, condenser, distributor cap, points and coil. However, I still have the same problem! The car will restart once everything cools down, before conking out again shortly afterwards. The coil gets very hot, and a friend of mine is convinced that this is the problem. If anyone has any suggestions, I would love to hear them!
Thanks...

modern coils and condensers can be absolute rubbish, go for really good ones. Have you checked the valve clearances? these can cause your described problems.

^^ x2 on checking the valve clearances first.

When changing all the above parts, did you also fit a new rotor arm?

Some Fiat models used a rotor arm with a built-in resistor, this type could give the symptoms you mention.

If the rotor arm is a resistor type, this resistor is positioned between the centre contact and the brass tip, it'll either be an obvious resistor (small whitish cylinder) or embedded in resin?
On the other hand if you can see a continuous brass strip between the centre contact and the sweeping tip, then it's a non-resistor type and probably is ok but it can be checked quickly as follows :-

To check for a faulty rotor arm (original points and coil ignition systems only NOT electronic systems) -
remove coil lead from dist. cap,
remove dist. cap,
turn engine, if necessary, to where the c/b points are closed,
turn on ignition,
Using a pair of insulated pliers, hold end of coil lead approx. 6mm from centre contact on rotor arm,
using a small screwdriver, flick open the points.
there should be NO spark jumping the gap between lead and rotor arm if the rotor arm is ok.

Al.

Hi I had the same problem and it was one of the plug extenders breaking down and giving a high resistance making the coil work harder and getting very hot and failing .Check them for resistance with a meter ( I will test mine to give you an example soon ) .Bryan

Hi

I had this problem. Changed the distributor cap and rotor arm and touch wood it's been fine since.

Changed coil packs, filters etc to find it was the cap and arm

Chris

I accidentally put a resistor type coil from an 850 on my 500 and had Similar problem. Right on 30 minutes driving spark would be rubbish and car would hardly run. Check it is the right kind of coil

Thanks very much everyone for all your help and suggestions. I should have mentioned in my original post that I did also replace the rotor arm, which I'm pretty sure doesn't have a built in resistor. I am trying to borrow another coil at the moment, to give that a try.
Bryan- apologies if this is a daft question, but what exactly is a plug extender?
Is that the HT lead?
Cheers!