Hello,

Try separating the linkages when you do this test. Make sure that both carbs are backed all the way down. Make sure that the secondaries are not partially open.

What happens when you adjust the idle mixture screw at this point? The rpm rise may just mean that you have the mixture screw adjusted too lean. What happens when you block the other vent hole? The mixture screws should be adjusted at the maximum rpm threashold. If the idle is too fast at this point adjust the small links to lower the idle. Carbs must be kept in sync. Re-adjust the idle mixture. etc.

There is a hidden horizontal passage in the idle circuit which when plugged is difficult to diagnose, I will try to post a pic here shorly.

__________________
Joe Alexander
Blacklick, Ohio
1964 220SE Rally (La Carrera Panamericana someday)
1966 Unimog 404s (Swedish Army)
1969 300SEL 6.3 (sold)
1969 280SL Pagoda
1973 280SEL 4.5
1974 450SLC FIA Rally car (standard trans)
1982 300D turbo (winter driver)
1986 560SEC
1989 Unimog FLU419 (US Army)
1991 300TE (wife)
2002 SLK 32 AMG (350 hp)