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Early versions used a drill bit index to adjust the choke break or pull-off opening distance. Later versions employed an angle gauge specification. Some carbs had both a primary and secondary pull-off. Note the linkage connecting the pull-off to the secondary air valve. A swollen diaphragm in the pull-off can either delay or limit the opening of the secondary air valve. For proper cold driveability, it is essential that the fast idle speed and pull-off opening are set to specifications. Q-jets are very sensitive to this adjustment. When out of calibration, either a cold stumble or stall will be present if the pull-off opens the choke plate too much. Conversely, not enough opening and the engine will load-up and blow black smoke when cold.