ORIGINAL: Hobbsy
When I had my .90 triple with the Keleo ring it made very little tank pressure, I was tempted to move the nipple over to right in front of where one of the exhaust pipes enters the ring.
When making and selling engines that are this complicated and expensive, there is no excuse for not engineering and including a working fuel delivery system. Fuel pumps and regulators should be considered mandatory for such an engine.
Another possibility is fuel foaming. Is the fuel tank mounted vibration isolated from the airframe? The size or the number of cylinders have nothing to do with an engine's susceptibility to air bubbles in the fuel.
And don't believe everything that you read on your fuel bottle's list of ingredients as being present or effective when there.
Ed Cregger