I don't know if it applies to this OS or not, but some OS engines had the remote needle valve assy mounted to a cast part of the back plate. Heat transfer caused the equalivent of vapor lock in the fuel and bad running. An extra cost OS change later fixed the problem.

Another OS issue I have experienced is the plastic needle valve housing cracked and allowed air to get in the line from the valve to the carb.

Or, maybe the high speed needle jet is clogged with debris or congelled oil.

Just because the tank is new, does not mean it is automatically without fault. Check to make sure all lines are clear and with no breaks or holes.

Sincerely,

Richard