The little steel cover on the carburetor that has four screws holding it on is the regulator cover. That cover has a little hole in it. What you need to do is solder a brass tube into that hole in the cover, and run a hose from it into the fuselage. What is happening is that as the cowl area is pressurized by ram air from the prop, it is being sensed by the carburetor and causing it to richen up. If you run a line to an area that is not being pressurized, such as the fuselage or somewhere outside the cowling, it will stop that problem.

AV8TOR