I normally get about 40 mpg with my red Z1. The blue one is just broken in and it gets about 40 with a close ratio tranny that revs about 500 higher at highway speed. Both bikes are stock intake, carb settings and exhaust.
I avoid ethanol when I can. In BC you can get Shell 91 or Chevron 94 without ethanol. The higher octane level makes no difference to mileage. It's just a bit of a waste of anti-knock additives....at 8.5/1 the Z1 engine doesn't need high octane.
Almost everything else in BC has ethanol. Here is a link that will tell you which stations have it. Just change the province or state to suit you locale.
By Oldjeep: E10 drops your fuel mileage by about 5%. Carb operated motors need to be richened up a little bit when operating on E10. We've had E10 around here for over 25 years, never understood the whole "fuel gets old" nonsense - I store over 100 gallons of E10 per season in boats, snowmobiles, power equipment and seasonal cars. Never had a fuel related issue. Modern fuel comes with all sorts of stabilizers from the pump, so no snake oil needed.
Time isn't the only factor. Temperature & quantity also affect the fuel >> higher temps speed up fuel degradation & larger quantities last longer than small quantities. I see that you're in MN, so you're going to have cooler temps on average compared to someone in hotter climes.
Here in TX it's hot hot hot for as long as 5-6 months w a couple more months of warm weather & sometimes there are almost 9 mos of hot weather >> the small amount of fuel in the carbs can go bad in a couple of weeks during those months. I've experienced it numerous times over the years & the fuel will effuse a distinctive acrid odor. ....
The EPA also mandates different seasonal and regional additive blends. I have a friend who owned a repair shop and the last few years a major portion of their work has been rebuilding gummed up carbs. Some from sitting for only three weeks. This is something he saw none of thirty years ago when he opened his shop. I have experienced it myself.
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough
I've been seeing more drastically gummed up carbs in the last 20 years, but it's always been due to vinyl or urethane fuel lines or more drastically kreme coat tank liners.
I let my bikes sometimes sit for a year or more if I'm working on or testing one of the other bikes, and haven't really had any gumming issues. When I open the carbs I only see a very light fuel stain and maybe a small dot of super-fine rust in the bowl... just like since the 70's.
I am also in a pretty cold-winter climate. It's only hot here for a couple months.