I have a poulan 3300 that will not pull fuel up to carb. 2 carbs ,one off of running saw, one rebuilt to try it. Impulse line seems to be pulsing can feel it. Tried fuel cap to make sure. New fuel line, cannot find fuel leaking. It has vent tygon with screw ,old Stihl style. Even tried pulling vent out plugging it to pressurize tank more. It has walbro hda 49. Have some stihls great saws ,but I really enjoy these mag case poulan. Thanks in advance