The vaporization of fuel is an endothermic process. As fuel is converted from a liquid to a gaseous state, heat must be added. This heat is removed from whatever is closest, in this case the throttle body. As the air is also cooled, water may condense from the air on the surrounding surface(s), and in severe cases cause icing.
GENERALLY, this condition is indicative of too large a carburetor (lower venturi air velocity) or too rich a mixture (possibly a choke not working, or no heat to the carburetor).
Inline engines are significantly more susceptible to condensation/icing than V's as carbs on V's normally reside above the valley where there is more heat.
If the installation is an integral automatic choke, some inline installations have a heat baffle in front of the integral choke to protect the choke from air movement from the fan, which could cool the choke to the point where the choke doesn't obtain the "off" position.
Would be nice to know which YF you have; Carter made hundreds of different ones for engines from 130 CID to 331 CID. One size does not fit all.
Jon.
