Yeah it sounds like your carb metering diaphragm is reacting to pressure changes inside of the cowl. Like mentioned, you can solder on or epoxy on a tube or fitting and then route a tube from it into the fuselage someplace where the air is static and that should solve the problem.

A intake stack is not a bad thing to put on either. A side carb engine setup tends to spit fuel and the stack helps alleviate that and also stabilize the airflow into the carb. The main jet is mounted high in the carb and tends to be affected by the fast moving air blowing past the carb's intake.

reference: http://www.prme.nl/forum/viewtopic.p...b50e44b92723d0