Hi Gil. Are you using muffler pressure? The .295 vent with a .155 dia spraybar would allow for a lot of power but probably not without MP. The largest vent that comes with the engine (the shorty) is about .277 id. You can drill it through and put the valve through and come pretty close. I've been playing around with the fuel consumption issue and found that making an insert with a sharp edged hole on the bottom has a fair sized effect on improving the fuel consumption. If I were having someone make one for me I would go with the .272 with the sharp hole. You can always make it bigger.