I hate huge carbs, I never run bigger than a 15 and my peds rip (and don't suck gas) because they are properly tuned. But since you already have the VM20, some observations:
If you had to go way lower on your main , you would see a black plug. If you don't , then look elswhere.
i am not fond of that piston port kit with a big carb. They can be finicky and getting the port timing right is problematic. I really do think you will have better luck with a different kit, or keep trying different base spacing. It is not burning all the fuel. I would bet your pipe is showing signs of this (wet inside) if you stand the ped up on it's rear wheel blackened fuel will drip out