could be carb icing, does it happen instantly or does it get worse the further you go
does that include the pipe and shroud on the exhaust manifold, and have you checked the warm air flap is actually opening when the engine is running
If you have jammed it on the hot only setting, then there is no point having the hosing to the wing! Take that away, as i suppose you could be cooling down the hot air too much, and causing the problem again. Also, check for sure that the hot air pipe is attached properly to the air box, might not be a good fit?