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I have a 350 that at WOT will start to bog down only to surge back up again on its own. When I reduce the throttle to 3/4 there are no issues and it will maintain the RPMs will no issue. I have a clean VST and all filters are also new. Only ethanol free fuel and the primer bulb is also new and does not flatten down when running. I am thinking an air leak from the fuel line leaving the fuel sending unit to the inlet side of the water separator. Any ideas would be helpful. I have also (last year) replaced the high pressure and low pressure pumps so I do not believe this to be the issue.