Here's some info on the 2 carbs, I suppose if you turn the bypass screw all the way in you effectively turn it into a non-emmisions carb like the other. The bypass screw allows the emissions to meet the standards of the day. The mixture screw on the emmissins carb is the smaller of the 2 screws so both can still be adjusted there:
INAT 32/40 and 35/40 two-stage carburettors with mixture recirculating system
Apart from the mixture recirculating system and a few other minor changes, this carburettor is identical to the INAT without mixture recirculation. Apart from the additional mixture recirculating system, the carburettor still retains its conventional idling system (Fig. 1).
Fuel for mixture recirculation is taken from the float chamber, metered through a fuel jet and supplied to a bore into which the air correction pipe projects from the top. The pipe opens into the mixing chanter. In this bore the fuel and air are blended to form an emulsion. A jet governs the emulsion flow rate. The emulsion passes into a passage leading down and is there mixed with fresh air drawn in via the mixing chamber. The recirculating mixture regulating screw has a taper which alters the cross-section of the passage without affecting the basic idle setting (the airflow through the throttle butterflies, preset on the carburettor test bench). (Fig. 2.)
The fuel-air ratio remains largely constant at both small or large flow volumes, and complies with the exhaust emission regulations.
Adjustment of engine idling speed and carburettor synchronization while remaining within the exhaust emission limits for each carburettor (with exhaust probes 13 0 020 in both exhaust manifolds) must only be undertaken at the mixture recirculation regulating screw (for engine speed) and the mixture regulating screw (for exhaust emissions). Use the air cleaner simulator 13 0 000.
Warning:
The settings of the throttle stop screws must not be altered, or else the throttle butterfly gap and thus the airflow preset on the carburettor flow test bench for the basic idle speed will be lost.
The carburettor manufacturer supplies plastic caps to protect the throttle butterfly stop screws.