The heat riser is there for a good reason and should be working for best engine efficiency.
There is a thread somewhere on this subject.
There is good scientific theory behind it. Something like , too hot a fuel charge and the engine runs lean , too cold and the fuel does not vaporize properly with subsequent puddling in the manifold and or washing of the bores etc.
The exhaust stove never heats the incoming air, nor the fuel in the carb to any significant degree (remember, its not hot till the motor runs for a few minutes). It can warm the carb up... but the carb is designed to measure the weight and rate of air and meter fuel accordingly. I do agree that it will, after a while, get rid of fuel puddled in the intake (which can be easy to do by over choking the carb). But even then, on a cold motor, its useless.
The only direct mention of the hear riser I can find in the 54 Truck Service manual is page 6-57, and that's to turn off the auto-choke. Which was optional to begin with. Model BC carbs were only equipped on trucks with automatic transmissions.
ALl 3 of my 40's vehicles, 42 Ford, 43 Chevvy G506 and 43 GMC CCKW have a very thick insulating spacer to do the EXACT OPPOSITE of what you say. The insulator keeps any heat FROM the carb. That's on 3 vehicles, from 3 manufacturers. So I gotta say that heating air/fuel is not what they had in mind.
