Just had the same problem. It reminded me of the same symptoms on an Alfa Romeo many years ago. The solution was the same - clean out the jet. As an earlier reply said the engine is running too lean and choking it improves the mixture. In the case of the A-4 it was my idle jet that was plugged but it could also be the main jet. It might be possible to clear it by turning the idle adjusting screw in and out and then returning it to it's original position. This time though I had to disassemble and clean it.

Moyer Marine sells a secondary fuel filter kit that fits between the fuel pump and carb. Not to replace the main filter but to give you a second chance to catch the crud. I am installing one this weekend.