1973 Mark New Owner Questions

Hi Bill –
I bought a Mark IV Continental last week, but it broke down on the journey home, after 100 miles. It was running very well, for around 80 miles, but then, after a coffee break at motorway services (I am in the UK by the way) it started misfiring slightly. This increased over the next few miles, and it also started backfiring too, then it eventually lost power. The engine doesn’t smoke, but what with me only having just bought the car, I have no history of how well it ran, except for the previous owners comments. The previous owner said “It has had a new coil, rotor, cap, condenser, points, plugs and leads and I’ve set dwell and timing carefully.” – and they do all indeed look new. Also, he recently restored the fuel system, as the tank has an internal rust problem, so he sealed it, and replaced the fuel lines, filter and cleaned the carb. I was wondering if your knowledge could shed some light on possible causes of the failure. I did fuel up with regular unleaded at the start of the journey (I was told the Mark IV can accept unleaded), and since the breakdown, I have tested for earthing/wiring issues, and found none. There also appears to be no problem with vacuum in the fuel tank. Tomorrow I intend to check spark and re-check the fuel pump and filter. One other thing – the fuel cap doesn’t lock on this car, but I have seen a locking cap on eBay for “1970 Lincoln Continental California only cars except Mark III” – so would this also fit a ’73 Mark IV? – Fuel is very expensive here in the UK ($6 per US Gallon) – and so I don’t fancy anyone siphoning my car. Thanks in advance for any help you may be able to give me.
Mark
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Greetings Mark –
From your description I also would first suspect a fuel problem as you do. You could begin with a fuel pressure / flow test as per the Shop Manual or inspect the fuel filer and the pick up sock in the tank. The aged fuel pump can also be a candidate for failure on these vehicles. Another result of debris in the fuel tank and lines is that some “fine” rust has entered and contaminated the carburetor. Checking the above should find or eliminate a fuel issue.
Sincerely,
Bill