The rule of thumb I've always used for estimating fuel consumption for a properly tuned 4-stroke glow engine is 1 ounce per cubic inch per minute at full throttle. So a 1.20 ought to use ~1.2 ounces per minute. A 14 ounce tank should give you at least 11.67 minutes of run time. 16 ounce = 13.33.

I've got one of these engines on a Great Planes P6E with a scale Keleo Creations exhaust and it's been great. Enjoy!