Ohh I started something here.....
That is NOT the rotary valve model!
The rotary valve model carby track is cast into the bottom half of the crank case and the valve is cast into the output shaft of the crank. The inlet air fuel mix goes through the centre of the crank output shaft and into the engine crankcase that way. The timing is controlled by the location of the inlet port cast in the lower crankcase housing which lines up at the correct time with the on core cast into the crank.
Ty I'm >99.999'% confident that you have a piston port controlled induction motor there.
There is a rotary valve model same as the old boy had is appearing in the Random photos as I type (the orange one with the cowling misssing and the "T" push handle with the individual wheel hieght adjusters, which the old boy tells me were for running along the concrete to get a neat egde on the lawn).... note the inlet although not as clear as I would to really prove the point, however if your know what your looking for......
John
