This vintage magazine advertisement features a mechanical device that was designed to be attached to an ordinary bicycle to convert it into a two-cylinder motorcycle. They called the attachment The Johnson Motor Wheel and it was manufactured by the Johnson Motor Wheel Company of Chicago, Illinois. The speed of the crafted motorcycle was between 6 and 35 miles per hour and one gallon of gasoline was good for 150 miles of travel. 

Here is a black and white clip art version of the bicycle converted to a motorcycle.

I scanned the original advertisement from the September 6, 1917 issue of Hardware Age magazine.

Click on images to enlarge.