The circumference of that axis (20mm diameter?) of the chainsaw should be 6,5cm.
With around 12.000 rpm of that engine at full throttle, the axis should revolve about 200 times per second - 6,5cm for each revolution
So the speed transfered to the wheel (Those tires on that bike shown won´t work..) is 1300cm or 13 meters per second - that´s (13 x 3,6) 46km/h.
So this might work - with around 4 horsepowers the engine has enough power.
In my eyes, the question is what will happen when the engine is cranked to full throttle?
Like flipgun said - the clutch ot that chainsaw has been removed..
So either you could engage the engine at around maybe 35km/h - or just kill it with the mass of bike and rider.
i've been working the 'oll chainy all weekend and everytime I'm pleasantly suprised by the power my little stihl has. I'm absolutely sure it will move the bike. Knowing you can doesn't mean you should though I'd keep my chainy for cutting