Dean, I can speak from hard personal experience. I have a 12 gallon header tank and it had a brass elbow sticking out of the fuel cap aimed directly at the prop. No problem with 30 hours or so taxiing (high speed and slow). On my first 3 flights the KR2 1835ccGPVW took off and climbed out well. However, as soon as I leveled out and the speed built up, the engine stopped and wouldn't restart in the air. At first, I thought it was vapor lock as Houston really gets hot in the summer. But after insulating the fuel system, the same thing happened as soon as I leveled out at 1800 ft (under the TCA). After the 3rd flight and the same result, we finally suspected the fuel vent - after some good advice I got from the netters. I extended the vent 6", pointed it into the prop blast, and also drilled a #40 hole just behind the 90 degree bend - to prevent overpressurization. I've put about 20 hours on my bird since with no further problems.
It seems that the AOA was the key, and the bow wave over the cowling at speed produced a negative pressure area at the fuel cap. Hope this helps, Don Sprague KR2 N118DS Houston, Texas
