Is gas getting pumped to the carb or is there just gas in the line? Get a friend to crank the engine and see if gas actually pumps (for safety, catch it in a container or attach a pressure guage).

You won't see much, if any, gas under the Stromberg topcover and diaphragm. These carbs have a separate float chamber fastened underneath, with an inlet float and valve that could be stuck or clogged. Be sure to correctly align the rubber diaphragm when you reinstall it - there's a little 'tit' on the edge of the diaphragm that fits in a little hole at the rim of the housing.

If fuel IS getting into the float chamber, check the enrichment device. It works like an automatic choke but it's actually a valve that lets extra gas mix in the carb when the engine's cold. It could be sticking too. There's a tiny slot next to the enrichment housing (round part with 2 small coolant hoses attached) through which you may be able to see the mechanism move, otherwise you'll have to remove the enrichment housing for a better look.

Finally, there's an electric fuel cut-off solenoid fastened to the main jet on the bottom of the carburetor. You should hear a click when 12V power is applied.
(I don't remember if power opens it or closes it and there's little mention of the Stromberg eletrical circuit in my W115 manual - perhaps someone else here has more info)

Happy Motoring, Mark

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DrDKW