As well as my indicator lenses needing attention, the saab is missing at idle.

About a year ago it was only running on three cylinders so I changed the spark plugs and that seemed to fix everything. But now it is starting to miss again. I have checked the distributor cap and leads, and they all seem to be fine. The only thing that comes to mind is that I havent gapped the spark plugs yet. What else could be the problem? If the gap is the solution, what would be an easy way to gap spark plugs without a gapping tool?

Thanks,
Ivo

Make sure you're using decent plugs, NGK BP6ES are best, gap to 25 thou with a regular set of feeler gauges (no special tools needed ).

Check condition of points and the gap/dwell angle - IIRC gap is 15 thou (sorry I work in old money, not metric) - if surface of points is pitted then replace. Replace all plug leads & dissie cap for the sake of a few quid. Might also be worth changing the condensor, and even losing the clockwork ignition for electronic (Pertronix is highly regarded over here).

Obviously check timing - 10deg BTDC at idle with vac hose disconnected.

If still missing then with a pair of insulated pliers/pipe grips, carefully disconnect one plug lead at a time to isolate which one is missing - it's the one that doesn't make any difference when lead removed!

If you can't find any ignition-related issues, check tappet gaps (if too wide you can get a misfire, too tight and the pushrods can bend/cams wear). Also check compression to see if you have a low CR in one of the cylinders - might be a sign of head gasket or other trouble.

Might also be fueling - is the carb set up correctly? They can be sensitive to mixture. Unfortunately (for help from UK bods) your very late car will have the twin choke Solex which was never fitted here, and they do come with loads of emissions control [expletive deleted] at that age which can cause problems. All said, it sounds like a basic ignition problem so far...let us know how you get on.