My old XR600 Honda was an early model with twin carbs like that, and while I didn’t paint on any white lines - I could feel the transition from the first to the second carbs - it did the same thing. Run up to the point before the second carb opened and it did amazing mpg (for a 600). I could regularly get 80 to 90mpg. Ok, you were only doing 45mph but if fuel was tight or you were happy to trundle along it paid off.

Carburetor syncro
 

The xt600 attached manual instructs that the second carburetor should start opening when the first is 7mm open. So one needs to delay this more to increase the fuel efficiency. But power will be lost as the second carburetor cannot open fully anymore.

I remember that 80mpg day in Mali. Exceptional, I admit, but marking the 2nd throttle helped.
Started with the first of many thorn punctures collected along the track to Gao, then turned into a miserable day slumped over the tank at 50 with frequent stops as my guts were doing a lot less than 80mpg.

20 years later, one night I got 87mpg from an injected 660Z chugging over the Atlas and averaged 20% more than my 1.5 carb Teneres.

In the 70s i had a 140V Bonneville and a mate had a TR7V - same motor but one carb feeding both cylinders. Surprisingly, I seem to recall our mpg was near identical.

https://adventuremotorcyclinghandboo...7-puncmali.jpg