You're welcome. Much to learn even with basics on these cars. Couldn't do it without these forums.
I'm not sure what you mean by "with tank hose disconnected and plugged" (the 14 mm hose from tank to fuel pump? or ??? just to keep solvent in tank?).
After battery charge and priming, mine started easily - is right where I left it a few months ago (sounds like one cylinder has slight misfire [guessing a dirty injector]), but doesn't die with only 1 (less than 5) gallon(s) of gas in tank.
I'm still confused on why so much gas (10-12 oz) came out when I blew air into return line - it didn't take much air flow to do this. It looks like the inlet hole is in bottom of swirl pot, but maybe the tank is lower (a small "well" outside of swirl pot) and the venturi pulls in fuel from the well. After seeing the venturi diagram and the alternate swirl pot photo (on pg 1 of this thread), I wonder if there's an opening in the bottom of the venturi (labeled 'suction' in diagram).
Some tips if not done so:
1) While pulling the strainer, etc down, change the 14 mm braided fuel lines (I wasn't prepared and 14mm line can be hard to find locally - cheapest I saw was here, but I don't know quality
Shopping Cart ). Bad to find the short hose is leaking at 3 am (soon the crack clogged up with rust particles [today is dried rust residue on outside of hose]).
2) Start clearing lines at the tank (I started up front and pulled/likely deposited gum through the long line from the tank to engine).
I'd do this quick check before attempting to pull carb cleaner through return line:
Remove the short rubber hose on the return line near the tank (enters at left front/drivers side of tank) - then connect a piece of rubber fuel hose to line from engine and (secure it) into container - energize fuel pump relay (or on/off key a few times to get 2 second flows) and fuel should go into the container [this checks everything from tank to engine and back to tank] - you can check flow rate at this point if you jumper the relay socket pins.
Then connect rubber fuel hose to return line going into tank - you should be able to blow/compress air into it.. if not, it's clogged (then try jamming a wire into it - I used ~2mm soft steel wire with a mashed 'hook' on the end to lessen chance of hangup). This thread details from beginning of clog and has some good info from posters
Fuel Distributor leak caused by clogged return line 1983 380sl - PeachParts Mercedes ShopForum
3) you may want to make a "trough" to catch/direct gas/solvent when draining the tank with the strainer out - it ran and dripped everywhere - the large pan caught all, but gummy gas makes a mess.
Photos show what was in the tank. First is from last cleaning (that was a clean galvanized pan), and second is what I kept pouring into a large coffee can (minus a few leaves) - is 1/8-1/4" of gunk.
I can imagine what is still in the tank. It'll probably need a good spraying with solvent. The best it could be is like the galvanized pan after pouring out the gas/solvent/deposits, which isn't clean at all until I wipe it down.