I always check out the spark before the gas 'cause 9/10 it's the spark. These old buggers have dodgy distributors, and the coils can go intermitent too. I was plagued by a weird condensor problem for 2 months once. I know this is more cash but an electronic ignition in there ( a scrap one from a 75/76 240 with a b20 is the best cheapest). Watch out for the cheapo caps and rotors out there, once I put in a new c&r and it ran worse. Itseems like they are making molds from none original stuff and the fit is getting rough. That's another reason to go electronic.
i don't know the injection system on these cars but check the electrics to/from any of the control stuff carfully. If the fuel sys needs feedback from controls it may not be getting good current from the ign key switch. I had this problem about 8 yrs ago on my 65, the insides of the key switch start making intermitent contact, very confusing. One of the most charming of which was refusing to give cureent to the strter in the rain, and you know how we all love to trip the solenoid in the rain.
Oh and here's my favorite "i'm lost" diagnosis trick. Pour a little gas (a couple teaspoons full)into the intake as close to the engine as you can get. Tryt starting, if it starts right away and then dies you know you have a fuel problem.
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patrick of montreal, '66/120, '83/245.