Id try to shorten the float bowl reference line as much as possable and make sure its not tee`d off for any other purpose. Its just a guess But if there is any delay between when when the carb venturi gets pressure and the top of the bowl gets pressure the fuel wont flow till it balances out. Bit of a wild guess really!

Try and get hold of a wide band oxygen sensor. This will help diagnosis and will be needed to get mixtures right.

Keep us informed

EDIT: the referance line must go to the top of the carb/hat area. If its going to just after the turbo it will seriously flood as boost starts.