Carb Question

What causes the throat of the carb where it bolts to the intake to frost up?

Venturi effect. As air flows through the carburetor the reduced diameter causes the air velocity to increase which reduces pressure. This pressure drop has a cooling effect. Adding fuel to the mix cools it even. Moisture in the air condenses and shows as frost on the carb. This frost can build up on the inside reducing throttle opening and causing poor engine performance especially at WOT. Or something like that.
I had that issue roading the 170 home in January a couple years ago

youi might be able to do something as simple as wrap a little aluminum foil around the manifold / carb ... but getting the air inlet below the hood is a great idea..

I had a Ford LN-800 medium duty truck decades ago, equipped with a Super-Duty 477 V-8 engine. I always would start the engine and give it a few minutes of warm-up time before heading down the road. Two or three times a year, if the ambient temp was just right, the humidity was just right, the barometric pressure was just right, the dew point was just right and the moon phase was just right, as it warmed up, it would slowly frost over under the big HOLLEY 4BBL carburetor, and literally choke itself dead. All you had to do was just wait a few minutes for the frost to dissipate and fire it up and awaaay we go !!!

Edited by DrAllis - 8 hours 42 minutes ago at 8:02am

Tbone95 wrote: Les Kerf wrote: Gary Burnett wrote: So is there a cure? Our vintage tractors are not well equipped for dealing with carburetor icing. The cure is to introduce heated air into the air stream ahead of the carburetor. I have driven old Ford pickups that have the 300 cubic inch inline six engines for the past 40+ years, these reliable old workhorse engines are notorious for carburetor icing unless the thermostatically controlled hot air stove on the exhaust manifold is properly connected to the air cleaner and fully functional. I prefer the early 1980's 300-6 pickups because I can buy them cheap since almost everyone thinks they need a V8. Of the five I have owned, only one had a fully functional air cleaner because the previous owners (all named Bubba) thought they were smarter than the Ford engineers who designed them   Yup, they iced up until I could get the hot air stoves working. The worst conditions for icing are generally when the air temperature is just a few degrees above freezing with high humidity and cruising at fairly high intake manifold vacuum. Had a 1980 F150, 300 6, 4 speed manual. Yes, the engine never gave one hint of trouble but had 3 various transmission issues in the time I owned it which was 5 1/2 years. About then I got my first big boy job and bought a new car. My father in law was on hard times so I gave him that truck (right after I replaced the radiator). He drove it a few years until it rusted out so bad he was dragging the gas tank down the road by the fill hose. Never an engine problem though! But holy cow did it rot away. Hard to believe there’s any of them on the road past 20 years old, but I do see them from time to time.