I do admit that I drive fast. The section of the GSP where I commute runs 75+ MPH on a daily basis. But that has been very consistent, with no changes in recent months that would explain the drop off.
If I drive the Double Nickel, aside from being a hazard to navigation, I would get about 300 miles per tank. But I only did that a couple of times as an experiment.
Check for any loose nuts behind the steering wheel.
That happens to me all of the time.
Then I’d say low tire pressure, something wrong on fuel injection or CC timing control, or the like. Or it just could be the fuel. I HATE ethanol! It destroys seals and gaskets, O2 sensors and a whole range of things.
I’ve had gaskets, seals and diaphragms on 2 cycle engines just dissolve because of it in regular gas mixed with 2 cycle oil. I’ve had to rebuild every carburetor in all my yard engines.