Collan, it sounds like you need to start from the basics with that engine. Go through a full tune up, doing things in this order:
1) check the plugs are clean and their gaps are right. In fact, if there's any doubt about how long they've been fitted, it's probably best to fit new ones - even then, check the gaps before fitting!
2) check / clean / replace the airfilter and any in-line fuel filters. Both of these can affect carb settings later on, so get them right at the start.
3) clean (or replace) the points (contact breakers) and set their gap. Problems here are pretty common with an engine that doesn't see much use, especially if it happens to have stopped with the points open last time it ran. Open points will corrode slightly, giving a much weaker spark. Remember that setting the points
will affect the ignition timing so you MUST reset the timing AFTER this step!
4) set the ignition timing. This is
essential after you've set the points gap because it
will change. I don't have any photos of a 66 engine I'm afraid, but the basic method is the same for everything:
Find the timing marks. If you have a manual available, use this to help identify them. They vary quite a bit from one engine to another but often take the form of
either a groove on the front pulley and a pointer or scale on the engine
or a pointer on the engine and a series of grooves on the pulley. Once you've identified the correct marks it's a good idea to put a little white paint on them - it makes spotting them easier next time!
Next, look at the base of the distributor, where it's attached to the engine. Usually you'll find either a clamp with a single bolt or a flange with 2 or 3 slots and bolts going through them. In either case, if you slacken the bolts slightly you'll find that you can turn the distributor body a little bit either way.
To set the timing:
Remove the distributor cap
Line up the timing marks by carefully turning the engine (by hand) in it's normal running direction. While you're doing this, note the direction that the rotor arm in the distributor is turning.
Turn the distributor body fully
in the same direction that the rotor was turning to make sure that the points are closed. Then turn it back the other way, very carefully, until the points
just open. There are a few ways to gauge this.
If you have a multimeter then the easiest is to set it to read resistance and connect it to the distributor wire and earth (make sure your ignition is turned off!!). While the points are closed, you'll see a low resistance but, as soon as the open, the resistance will jump to infinity.
Without a multimeter, you can connect a spare light bulb in the same way. Switch the ignition on and, as the points open, it will start to glow.
If you don't have a spare bulb then take the HT king lead (from the coil to the distributor cap) out of the cap and fit it to one of your spark plugs. Rest the body of the plug against the engine and, as the points open, you'll see a spark across the plug.
Once you're happy you've got the right point, tighten the distributor bolt / bolts and then turn the engine through a full turn (again by hand). If all is well, your meter / lightbulb / spark-plug should show the points opening again just as the marks come back into alignment (they'll also open once after half a turn, but don't worry about that!)
Once you're happy with the timing, put everything back together and start her up. Run the engine long enough to make sure it's warm, then you can set the carburettor.
Start by adjusting the idle stop (NOT mixture) screw to get the lowest speed it'll keep running at. Then adjust the mixture (or volume) screw to get it as FAST as you can. Adjust the idle stop down again to the slowest it'll run, then adjust the mixture again to speed it up. Keep doing this until the mixture screw can't be turned in either direction without it running rough or stalling. Finally, use the idle stop screw to bring the idle speed back up to where it should be. With a little practice you can get an engine well within MOT measurement limits like that without an exhaust analyser
Hopefully, someone with a 66 can fill in the details, such as what the correct marks are for that engine, how the distributor's clamped & so on?
Joe