1928 Hudson Starting Problem

Unknown

Hi, everyone.  I recently purchased a
very nice 1928 Hudson Landau Sedan.  The car is very hard to start when
cold and worse when it warms up (the original Marvel carb has been replaced with
an updraft Zenith of unknown pedigree).  It also tries to stall at stop
lights unless you grab the choke.  Although I haven't shaken it down, I
suspect a vacuum leak in the heat riser setup.  Any suggestions (and if
there's a leak inside the heat riser is there any salvation)?  The engine
pulls fairly strongly and smoothly once you get rolling.

 

Thanks very much,  Jim Gilbert