ORIGINAL: [AKA]StraferX
Their on the bench I realized that the nipples for the fuel line from needle to carb were loose and that their gasket was coming out..Replaced gaskets and tightened the nipples...Problem solved.
This happens with a LOT of engines where those heavy stock paper washers are used.
Also cap screws on a new engine tend to get loose after the engine has been run for a bit.
It's a good idea to tighten everything down carefully on a new engine, after it's first tank or two.
You'ld be surprised at how often the cylinder head is loose on broken in engines.