Grey Fergie Tef20 Not starting.

[tomlad]

There is a butterfly, the linkage arm is sometimes missing.

 

[Ley253]

oil bath air cleaner over full can cause the same problem as overfilled sump

 

[MrNoo]

There is a butterfly, the linkage arm is sometimes missing.

Yes they wear quite badly, same as the spindle on the back of the pump, easy to machine out and re-bush. They do seem to still run surprisingly well with a lot of wear in mind. The stop lever is connected to a lever on the pump itself which I believe is connected to a cam that works on the rack. Been a while since I had one apart so cant remember.
The vacuum works the rack, so the more you open the throttle lever the venturi will open and create more vacuum and hence more fuel is thrown in, less vacuum and the rack cuts fuel in.
If you take the side cover off you will be able to see the rack element quite clearly, this engages via teeth on each element, if the rack moves all 4 elements will move too (element is probably not the correct term but the correct term escapes me I'm afraid)