Well i have a 175 evinrude intruder. I was doing some trouble shooting. Seems to happen with this motor alot. I'am about to start comparing it to a harley. Anyway back to the subject. I don't have a antisyphon valve at the tank, i took it out. Brand new fuel line from tank to motor. I have a primer bulb and a see thru plastic inline filter on the fuel line. The filter is in front of the primer bulb. I start the motor and you can set there and watch it lose prime through the filter. If you take the hood off my motor at the fuel line connection is a see thru tube. You can set and watch air bubbles go past then it goes about half empty. I think the fuel tank is sucking the fuel back to the tank, syphoning it back. I was told i didn't need the antisyphon valve at the tank. What i'am i missing here. I know why my motor hasn't been running well but i don't know the root cause. I took the pickup tube completely out of the tank and leak tested it. Its fine. The vent is clear and the primer bulb and filter are in upright position for obvious reasons.This one has me stumped any help on the matter would be appreciated.