Carb Heat Passage

[jeepguy1948]

I’m about to get my rebuilt Merc motor back on the road. Per ‘Ol Ron I am going to stick with a single carb for the first 500 miles or so (in this case either a Holley 2100 or a Stromberg 48). On overhead valve motors I built in the past I always blocked off the heat riser passage (at least that’s what we always called the carb heat passage in the intake manifold). I’m wondering if blocking that off is a good idea with the Flathead? Or is it better to leave that open and install a heat insulator under the carb? Or both? I realize that the motor would be a little more “cold blooded” with the passage blocked.

 

[ford38v8]

I think a compromise works well. The risers being the diameter of a penny, drill a ⅛” hole in pennies, tap into the risers in the block. Use wheatstalk Pennies, as the metallurgy is best for the purpose. This will provide a cooler running carb, fewer stalls at stoplights, less boil over when you stop, easier restart after stopping for lunch, and perhaps a sweeter exhaust note. On the downside, cold blooded in the morning, addressed by the use of the choke till fully warm. The smaller passage holes provides a considerably less radical approach than fully open or fully closed.