Have you checked the CO and idle speed? Also the timing?
I'm not using a fuel reservoir (swirl) i'm using a t-piece in the supply and return. Did want to use a reservoir, but never bothered. The pierburg had one, but the weber didnt have a mounting point, and it didnt come with one! Can you put a picture of the reservoir please?
If you suspect fuel starvation, take the air cleaner off and have a look down the top. You can clearly see a jet of fuel going down when you rev it. Could be too much fuel and flooding it, gives similar symptons.