4M = early manual choke
4MC = hot air choke on early carb
4MV = early divorced choke
4ME = electric choke on early carb
M4MC = modified (1975+) Qjet w/hot air choke
M4ME = modified (1975+) Qjet w/electric choke
M4MEA = modified (1975+) Qjet w/electric choke & Altitude calibration
E4MC = 1980s electronic Q-jet w/hot air choke
E4ME = 1980s electronic Q-jet w/electric choke
