Ok, just guessing on the performance characteristics of this rig.

The guesses follow:

The pulley on the motor is 4" dia (or 12.56" cir)
The pulley on the pedal crank (no foot pedals) is 12" dia (or 37.69" cir)
The pulley behind the pedal crank pulley is 4" dia (12.56" cir)
The pulley on the rear axle is 12" dia (37.69" cir)

I come up with nine turns of the engine crank for one turn of the rear axle. (a 9:1 final ratio)

The rear tire I'm guessing to be about 26" dia (or 81.68" cir)

Thus:

The motor turning 3000 rpm (assuming it's 2 cycle) would generate 31 mph and turning 4000 rpm would generate 42 mph approx.

Understand this is based on guesstimation and nobody ever accused ol' eDJ of being a mathematician. (and we won't even go into volumetric efficiency of the motor cause it probably came out of a scrap heap anyway.....and Jose is
probably considering himself lucky just to have something that ran so he woun't have to walk)

By allowing the engine displacement to be 6.33 sq in via 2" bore/stroke churning 660 cu ft of air in one hour @ 15:1 fuel/air ratio then perhaps a milage of just under 60 mpg is possible with this set up. That's guessing one cu ft of gasoline mix was used to fill the tank. (which would be 7.48 gallons used per hour) not taking into consideration the few ounces of mix oil necessary to produce a 40:1 ratio mix.
Again guessing 40:1 is the ratio requirement.

But the fuel tank shown looks like it could hold about a gallon....so perhaps the bike could wring out a 80 mile run. (just going on the trend of 3/4 gal per hour = roughly 60 mpg)

How's that for guessing ? If anyone else here who is more skilled with numbers than I wants to take a crack at it I'd be delighted to hear your version.