I have a frustrating problem with a Ryobi 31cc conversion. It ran great when it was a weedwhacker, but now it's almost impossiple to get it to run. It'll run on the prime but doesn't draw fuel through the feed line. I choke the carb with my finger and crank the prop through like I usually do before starting and no fuel draws through. I've checked everything many times, changed gaskets, used gasket sealer and taken the carb apart to check for clogs, etc. Nothing helps. It's not the fuel tank, because I ran another engine the same day using the same tank. Could it be a problem with the reed valve, or what?