The answer to this question is huge! There are so many things that could be wrong, with the possibility of more than one fault, that without knowing the car or engine, it is almost impossible to answer in a few words.
However, let's first look at starting problems and a few things particular to these models. If you have a 1.6 model then one problem can be in the half-round plug that connects to the alloy, finned, amplifier. It has five pins/sockets and these are: one for ignition, another for earth, two for the connections to the trigger module in the distributor and the final one is for the screening sheath around that trigger wiring. If you pull the plug off the module and look inside the plug you should see the five sockets that connect to the five pins in the module socket. Unfortunately sometimes one (or more?) of these sockets in the plug gets pushed back further inside the plug. Now when the plug is pushed on to the module that socket won't make contact with the pin or it may only just touch. This leads to difficult or impossible starting and if it is just touching, it may be cutting in and out on the road, making you think it is misfiring.
The answer is to use a small 'pick' and carefully and slowly pull the recessed terminal back flush with the plug face and the other terminals. Make sure the terminal has no burrs and is round and it is going to slide onto the pin without getting pushed back into the plug again. But it must be a good enough fit to make clean contact. If the module has a fault be aware this module is almost impossible to get now as it has become NLA. Also beware of the U.S.Chrysler module that is similar but has a pentangle plug socket. This is no good for European Chrysler models (Simca/Talbot) and was only for the American Chrysler, Dodge or Plymouth models.
The 2.2 has a Bosch ignition system which is similar but with a small plastic encased amplifier alongside the coil both mounted on an aluminium plate bolted inside the inner wing. The metal backing of the amplifier is also its method for transferring heat to the plate for cooling, so corrosion here can inhibit the amplifier cooling. Also again check the plug and socket connections. Whilst there are six connections this time and all in a line, any faults here can cause problems.
There is an earth connection point nearby on the curved chassis around the suspension strut. As the chassis was fully galvanised, the zinc coating can creep back and reduce the earth contact after some years, which can cause starting problems, so you should remove the wiring, clean it back to bare metal and refit the earth wiring. Then cover with silicon to protect it. In fact there are about six earthing points on the car and this can apply to any of them.
Ignition coils are known to leak some of their oil and they are then not adequately cooled leading to ignition breakdown when hot. So if the ignition cuts out when it gets hot but will start again when it has cooled, check or replace the coil. In fact if the coil does not produce a strong spark, or is very old, it is probably worth replacing anyway.
Assuming you have had the Murena for some time and know it fairly well, and it has been running fine up to a certain time; ask yourself this: 'what was the last thing you did after which you started to have problems'. Maybe you have just serviced the engine? If you have just fitted new spark plugs for instance, many people forget to check the plug gaps before fitting them, and this is likely to be the first problem. This is an old car, but with electronic ignition and the plug gaps should be 30 thou (or 0.7 mm). Cars like the Bagheera with contact points in the distributor should have plug gaps of 25 thou or 0.6 mm. Most, if not all, new plugs now come from the manufacturer with much wider gaps for modern cars and engines. These will be at least 1 mm and often more. If you fit plugs with gaps such as these to your Matra you are asking for problems! So make sure the gaps are correct, and if you have a car with points and condenser, check that these are correctly set and working too, and the car should start fine, assuming all other things are good of course.
A second thing with older cars that is commonly forgotten when servicing the engine, is the advance weight lubrication. When the points were a common replacement item, one of the jobs that should have been done at the same time whilst inside the distributor, was to put a couple of drops of oil down the centre shaft - you removed the rotor arm and added a couple of drops of oil there. Why? Because this fed down to the advance weight mechanism underneath and kept them lubricated. Now that we don't have to replace points with our electronic distributors, the cap is rarely removed and the lubrication gets forgotten. Once the advance weights get dry and seize up the timing will suffer and if they are stuck in the advanced position, can make it difficult to start and affect the low speed running. So you need to make sure these are free and can work correctly.
If the car is new to you and you don't know its history, you are going to have to check everything from scratch as you cannot, or should not, rely on anything anyone else has done (or NOT done) before. This is one of the biggest problems people have when trying to get to the root of a fault - assuming certain things are fine! NEVER assume anything. The moment you assume something is fine, you will probably overlook the one thing that is important and be frustrated when you can't find anything wrong. I have seen this so many times over the years in this trade. I always start from basics and prove to myself at each step that it is good, and I have always found the answer along the way. Usually at that point the person who was having difficulty would say something like 'Oh I didn't check that as so and so said he had checked it or that it was O.K.' Need I say more.
So if the car is a new acquisition, and the engine an unknown quantity, then start from the beginning, remove all plugs and inspect them, remove the rocker or cam cover (esp. check all cam lobes on the 2.2) and check all valve the clearances. The plug condition and colour should give you some idea of how it was running. Whilst they are out, check the compressions. Remove the distributor cap and check the ignition system and timing. Check the fuel and system (esp. check idle jets). Let's face it, if you have good compressions (140psi or better, balanced across all cylinders), correct ignition and a good supply of fresh fuel, the engine cannot help but start! If it does not start easily there has to be a fault in one of those three areas. If the engine has been apart and rebuilt then you may need to check other things like cam timing, which can be tricky to get right and is sometimes one tooth out. Or the rocker arms have been fitted incorrectly (2.2), inlet and exhaust arms are different, but many times I find them all over the place with inlets on the exhaust side and vice versa. And the cam lobes become badly worn. Or the engine has been replaced by a non-standard engine and is altogether incorrect. A Chrysler 180 or 2-litre engine is similar to a 2.2 BUT not the same...
One thing that is different to other cars, with the Bagheera and Murena, is that the Matra have vacuum operated pop-up head lights. As these get older the vacuum system can leak owing to cracked and perished hoses, or a poor switching valve. Any air leak into this system will also cause the mixture to be weaker as it will also enter the engine without having passed through the carburettors. So make sure this vacuum system is air tight. Another possible consequence of an air leak into the head lamp vacuum system could be cylinder head cracking owing to running very lean mixtures and over heating in the combustion chambers, so don't ignore this. A quick test of the vacuum system is this - can you raise and lower the head lamps when the engine is NOT running and has not run for some time? A good vacuum system can hold the vacuum for days. A poor one will not operated the head lamps as soon as the engine is switched off! If you have any doubts contact me, and I can probably help.
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