Starting an old engine ....

Regarding the gas tank:

Even if it doesn't leak and you can get fuel to flow out of it, you will probably have trouble with it in the near future. All the deposits and varnish that built up inside it are going to be diluted by the gasoline used today.

Today's gas has up to 10% ethanol, and it acts as a very good cleaner. Too good in fact. All that crud will begin to dissolve and will constantly clog your fuel filter.

Many boat owners with older inboard tanks had this problem around here about 10 years ago. Boat ran fine until the switch to the 10% ethanol. Then there was constant clogging of the fuel filters. A big headache on a boat!

If you don't have any trouble with the filter clogging, you are lucky. If you do, then this is a very likely cause of the problem.

Best of luck