To clarify: it got 14mpg with the carter and the NOS dist installed then ONLY the carb was switched to the holley (same dist) & the mileage went downhill?. Same ported or non ported for the can? I'm assuming there is a good reason why you dont put the carter back on there. those 1920's are so simple/fun to work with. I would wanna get to the bottom of it just for the satisfaction. I'd get some jets and recheck the float (level/saturation)/no base gasket or vac line leak. Holler how it turns out. not sure the 35 is right & I have one & I'll see if I can pull the bowl & see what jet is in it (not sure what year it is) but what I have outa tell us something. EDIT reread & saw the "terribly". describe that