below pic is the design reference for this build, Harley Davidson 1934 CAC Speedway by Joe Petralli. the entire dimension is scaled to 20" x 2.30 bmx tire so the chassis is smaller than the original design
the rear hub is coaster hub, so it will act as free wheel and brake when we pedal in reverse. for the left side, i make "left orientation" thread on the hub housing for the engine-driven sprocket. the engine is started by its original recoil starter and free as the stihl-modified centrifugal clutch is disengaged on low rpm. on higher rpm, the clutch is engaged and drive the pulley and then wheel sprocket. the pedal is freely when we run (we dont have to pedal very fast). similar case when we stop on traffic light, engine run in low rpm and clutch disengaged.
for the front wheel, its a modified shimano dynamo hub as i mount disc brake on it.
when we run out of gas, we can pedal the bike (bit heavier due to belt friction)
the fuel tank is hand made and at this moment still finding nice headlamp with tacho at ebay.