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Am I under standing this correctly? You think that the Cline fuel pressure regulater is actually supplying the fuel at atmospheric pressure. The diaphram might have atmospheric pressure on one side of it, but it has well over 5 psi of fuel pressure ready to be released when the engine needs it with just a slight vacuum pulse, that in my experiece even an OS 10 FP with an air bleed carb can supply. I have used Clines on everything from Saito 1.00 twins (twin Air Bleed carbs with a y and one reg.) to a Saito 300T, Big Super Tigers, and a little OS 10, and every little engine in between, and I have never ever experienced the problems you are describing when useing a Cline fuel pressure regulator which by the way the can flow well over 4 oz's a minute. I have one sitting here right now that will be going on a ST 2300 with a Magnum 1.08 carb and adapter as soon as the engine arrives in the mail. In fact i just machined the adapter tonight and will be useing it with a Cline Regulator that is 15 years old (new guts though). They simply do not wear out, and are the cats meow when it comes to making a stable running engine in my book. FYI, the Cline regulator uses Stock Walbro WA/WT parts, and can be rebuilt in 5 minutes for about $3.00 american money. There is no substitution in my mind, so why recreate the wheel with a chopped up Walbro carb.