The other knob is the fuel reserve . i suggest byou don't try and start it but drop the tank and reove the carb and fuel pump. Clean them all out so they are spotless .I have found that cutting the tank open and cleaning it is the only way to get them really clean. The pump may need a kit as will the carb/carbs. They are notorious for hard starting if ther fuel tank connections are crappy so ensure you are realy fussy about getting them sorted properly.
Replace the plugs,points,leads and cap . Caps etc are cheap enough on line and the best bet is the pertronix ignitor for getting rid of annoying points problems. Dump the old oil and filter and replace them and pour a mixture of 50% acetone and 50% brake cfluid down each plug hole. let it soak for a few days before trying to turn it over. Check that the water pump turns,it will probably be seized but they can be stripped and rebearinged etc.
Set the tappets and make the sure the chain isn't too loose and you should be ready to fire it up.
Mine sat for 30 years and ran like a top when I fired it up recently ,not too badly at all either with no blow by or knocks and idled nicely .I even took the carb off it gave it to mate who is running it on his 1953 220 .
These are mercedes after all
Now for real advice from those of us who not only drive these as daily drivers and fool about with them constantly you should sign up with the IPOG on yahoo groups. While not trying to put down a certain ACT company,their price structure sucks and many of the IPOG members can supply genny parts far cheaper and lots of sound advice based on experience without attitude.
http://autos.groups.yahoo.com/group/ponton/
