This will solve the problems you encountered: http://www.horizonhobby.com/Products...=ZEN848ES08300

Trying to "supercharge" the engine with the slipstream just doesn't really work. Even if/when you got it figured out to balance the pressures and get good carburetor performance, the gain is only around 1% power at common model airplane speeds. A lot of the gains you see on cars with hood scoops actually come from feeding the engine cooler air, not the ram effect. If I remember correctly, you gain about 1% power for every 10 degree reduction in air intake temperature from whatever your baseline is...

AV8TOR