Answered>Order 509

The engine has a single choke down-draft carburetor, with a 28 mm diameter

Venturi. This venturi takes the form of a convergent-divergent nozzle. The float level is 1 7/8

inches below the outlet – through small holes at the midpoint of the choke. It is standard

practice to feed the petrol in through such holes at the smallest diameter of the choke.

1. Please compute the main jet size for an optimal air-fuel ratio at 2000 rpm.

2. Please produce a plot of air-fuel ratio versus engine rpm and indicate the limitations

on rotational speed for this arrangement.