Sorry to sound like a broken record, but check out my post "carrier engine testing." The OS 4BK fits the same size hole as the Evolution carb, but with the spray bar all the way across the venturi opening, it seems to have better fuel draw. You will pay a 100 rpm penalty, but more than make up for it with a "no-falter" takeoff.
If you don't have a 4BK in your stash, watch ebay for a cheap OS 40 FSR. I think there's one on there now with a buy it now price of $35.00. Keep the OS carb, put the Evolution carb on the OS, and re-sell it!