First you need a rearrangement of concept. The lever that is attached to the rear housing has nothing to do with fuel correction while driving. It is a dampener to deminish the rump, rump, rump at idle by touching on the rack somewhat.

Manifold vacuum is what balances the rack position against the spring tention all of which is shimmed in a couple ways. So when you open the vacuum line you do two things. First you add a huge source of air and second you send the mixture rich. The combination results in engine speed increase and a lot of smoke.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician