I have a 10.5 oz tank suplying my Mac 32 and after about 12 minutes of flying at full throttle (it had a bit of a power issue) through 2 flights (tuned it, it helped a bit) it still had about 1/2 tank...

my instructer has a big stick (scratch built about 30 years ago) with an old but now rebuilt gas engine that's at 52cc, uses it to tow up sail planes, gets 3 tows out of a 12 oz tank with fuel to spare...