the hard starting when hot can be the starter getting too hot, although it sounds like the float bowl may be boiling dry ... the only baffle on the manifold is a plate on the underside held by small push in rivets - not sure that would have an effect on heat, but being right under the carb it might - don't have one handy to look at ... more likely the missing butterfly is allowing too much exhaust thru the manifold, I'd fix that for starters
Bill
