I can get the engine to start (after winterizing for a few months, now with new spark plugs) if I apply some throttle, but when I try to set the throttle lever to IDLE (Neutral) position, the engine quits. I can re-start as long as I give it some throttle, but each time I try to put throttle lever in Neutral, the engine stops. What's the likely cause? We recently had removed the gas tank, filtered the fuel, and re-installed and re-fueled (with the same gas). Also, when throttled, the engine runs better in a raised (tilted) position then when it is lowered all the way...What gives???