Originally Posted by Brutus1967
Higher velocity means higher fuel draw (the fuel pump/regulator just keeps the pressure at before the needles constant, the fuel is still drawn in by pressure differences in the venturi, as in any carburettor). Maybe that principle is used to influence the linearity and transition of the carburettor a bit. If that is true, it would make sense that a centered spraybar richens midrange, and a withdrawn spraybar leans it out.
Hi Bert my opinion,on this engine unfortunately pump/regulator system cant supply constant pressure before carb only because carb is glow style.What does that mean?Regulator needle reacting against pressure (vacuum) differences but at carb.like you said ,not at pump. In a glow carb max vacuum occurring at idle and near position.So reg. needle opens full to drown carb.When pilot adjusting the HSN,LSN according to this situation,then same adjustment begins not able to supply at WOT only because reg. needle restricting fuel supply now,because lower vacuum than before(idle position).So user must find a way to keep fuel supply constant before carb.Then engine is a champion.with a little header tank before carb.and removing spring and reg. needle and leaving only pump maybe means another solution.