Depending on the temperature and time, the opening of the air damper is controlled by a membrane mechanism -1- by a thermal valve with a time delay -2-.
When the thermal valve -2- is open, the vacuum is reduced by the ventilation flap -3- and the air flap is held in the first position (small gap, 1.7±0.2mm).
When the thermal valve is closed, a full vacuum is applied to the membrane and the air damper moves to the second position (large gap, 3.0±0.2 mm).
Examination
Remove the intake air guide see below.
Shut off the vacuum hose from the bottom of the carburetor body to the temperature regulator in the air filter housing, for example, plug it with a clean bolt of the appropriate diameter.
Start the engine and leave it to idle.
air damper (top carburetor choke) close by hand.
If the air damper closes easily to a gap of approximately 3 mm and then shows increased resistance, then the vacuum limiter is in order.
If the damper can be closed completely without resistance from its side, then the malfunction is due to either a crack in the membrane or a leak in the vacuum line. Check vacuum limiter for leaks.
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