Assuming you have checked all the timing and valve operation, think about the distributor. basically all it does is open the points at the right time and connect the coil to the correct plug. Only two active positions. Engine runs on one cylinder so turn distributor through 180 degrees and swap HT leads at plugs. Try not to disturb anything else. If engine now runs on the OTHER cylinder the is a fault with one position of the distributor (bad cam, bent shaft faulty cap whatever). If the fault is the same it's highly unlikely the distributor itself is at fault.
What type of pick up did the electronic ignition use? if it was the points, changing it will not have ruled much out.


Sometimes you can get too close to a fault and not see the "obvious" try standing by the engine with someone (does not have to be someone who knows about engines) and talk through everything you have done from the beginning. This can often help clarify what is going on and separate the "wood from the trees"


Robert G8RPI.

Is the spark plug on the non-firing cylinder becoming wet with fuel when the engine is run on one cylinder?

As several others have said, if the problem started only after the distributor was removed and replaced, then I too would be thinking hard about what might have been damaged/disturbed/upset during that work. Are you certain that nothing else was done?

Anyone playing tricks on you?? (e.g. you can have good compression and a spark at the right time but that cylinder won't fire if it's exhaust port/pipe is blocked....if a sort of hissing sound, similar to a football deflating, is heard after switching-off the engine, then you possibly have an exhaust blockage).

I'd try what 'fiat500' suggested and remove the rocker/valve cover but in addition I'd disconnect the plugs leads (leave the existing plugs in situ) and insert known good plugs into the leads, resting the plug bodies on the engine cowling (to earth them). Then with the ignition switched on, I'd turn the engine over slowly using a wrench/socket on the generator nut (press down on the slack-side of the drive belt if it slips), while watching what is happening. You'll be able to feel the compression building up on each cylinder in turn when that cylinder's valves are closed, as you near tdc, that same cylinder's plug should fire. One complete turn of the crankshaft later the process should be repeated on the other cylinder. Just before each spark occurs, stop turning the crankshaft and listen for gas leaking from the exhaust or back up through the carb.

If the engine runs on one cylinder, then you can eliminate (afaik) the ignition switch, ignition coil, coil lead, condenser and carburettor (if original single choke type). You have good compression on both cylinders, new spark plugs. The problem must surely?? be somewhere in the distributor (as g8rpi has suggested). Was it dropped? disassembled? any parts changed? Distributor cap sitting correctly in situ? Take a look at the distributor operation with cap removed while turning over the engine with a spanner/socket as suggested above, you'll probably be able to see a small spark at the points as they break (start to open). If you check the points gap (ignition switched off!), do so on both lobes, the results should be virtually identical, otherwise something is worn/damaged.

Al.

Gentlemen,

Thanks for all your replies, suggestions and recommendations.
I finally solved the mystery about this engine running on one cylinder after playing with the timing.
I once again checked the timing, fuel, valve clearance and compression. To my astonishment I found absolutely no compression in the second cylinder!!
After removing the head I found a failed head gasket. Never mind that I had checked the compression in both cylinders shortly before working on the timing and finding a healthy 125 psi in each.

Funny how something unrelated can crop up at the same time you are working on something and totally confuse you.

It also turn out that the distributor cap is of a 126 with the reverse numbers as is mention in an earlier post. That confused me too.

This is my first Fiat (actually an Autobianchi bianchina Transformabile) and it is fun to get to know the in and outs of these engines/ cars.

Thanks again for your help.