I'm close to getting a 67 Valiant back to running with another motor and I'm not sure what to do about the gas in the tank (if there is any, or much). The guy who sold me it said it hasn't ran for a year to a year and a half. Is this long enough to the point where I need to clean out the gas tank or should I just siphon whats in there out and put in new gas?

What does the fuel smell like?-- if it has an odor you will need to dispose of it--- or be very careful & use it for solvent.

If your engine is of unknown working order-- I would siphon the old fuel out. (eliminating a fuel problem later)
Lawrence

If you were here I would say run it but I hear the gas there is JUNK. I would drain the tank and clean out the lines. You may be further ahead by rebuilding the carb BEFORE you even try and start it. This way you dont push the gunk into the small tubes and orfices of the carb.
My02.
Frank

_________________
Scrapple: Because a mind is a terrible thing to waste.
73 Duster - Race Car
66 Dart Wagon - DD
178" FED
82 D150
All Slant powered

my dart has given me tons of problems bc of old gas, older than yours, but my advice would be to get the old out and at least take a look at the inside of the metal lines and replace the rubber ones, i finally redid all lines, new tank, new sending unit, and rebuilt the carb this summer and havent had any (fuel related) problems since then, used to flare up from time to time.