1918 Smith motor wheel, model C buckboard

 there is no accelerator pedal, just a brake pedal. To go at different speeds you raised and lowered the motor wheel. It went at a constant speed, and if you didn't want to go that fast you raised it occasionally to get something between stop and full speed.

for all you might want to know, or see about the Smith, which ran from 1915 to 1919 and then was bought by Briggs and Stratton, see http://justacarguy.blogspot.com/2010/01/briggs-and-stratton-flying-buckboard.html and for an engineering drawing http://justacarguy.blogspot.com/2011/07/4-wheel-buckboard-with-smith-motor.html