Have a gas engine that runs good on the ground, then goes rich at altitude. It will not clear out. Does not stop but loads up and loses power which makes for some hairy landings, having engine surging at low speeds. I have seen a post where the carb was vented into the fuselage, but can not find it again. The vent was off the 4 bolt/screw plate on the carb. My plane is a Yak55 with cowl. Any help thanks.