Diesel 1977 mazda parkway motorhome

Petrol or Diesel? Black smoke is the engine running 'Rich'. The mixture of air and fuel has too much fuel and not enough air. When was the motorhome's engine last given a major service? Clogged air filters can cause black smoke and clogged fuel filters can cause a power loss. Are there any warning lights on the Dashboard?
If a service doesn't solve this you will need to move on to other areas. Parts like the EGR valve, (Exhaust Gas Recirculation), and the injectors. The DPF, (Diesel Particulate Filter), on a diesel engine can also cause these issues.
You could get it plugged into a diagnostic system or a OBD2 scanner to check for trouble codes but this will cost you money. Ask at a few different garages as the price charged to scan the system can be VERY different between garages.
Comment below with more details about the vehicle and I'll see if I can help you more.

A 1977 1.3 was .010 intake and .012 exhaust . I'll keep looking through my old manuals for a 1979 .

Check around the base of the master bed.

We do not have any motorhome wiring information. You will need to trace the wiring back manually.

let it run for 3 minutes

prime after the fuel filter on the out feed pipe to pump !

Usually the shifter is on the dash instead of the column so the RV companies used their own design.
I would check with the RV clubs and research the internet for salvage yards for RVs and campers. Good Sam is one that comes to mind.
You may also find something that would work at a boat dealer.

There are 2 fuel pumps on the dodge motorhomes electric in the frame by the tank and the manual pump on the engine block

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