ORIGINAL: AA5BY
If so, it indicates the vent line has a kink that many times will allow filling the tank, but is closed otherwise and will cause negative tank pressure.
There is no vent line used for this engine, rather tank pressure is called for according to the manual.
That may be part of the problem too.
The engine does appear to have a pulse port, but the manual tells the user to install a muffler to tank fitting for pressurization.
A normal gas pumper should not need tank pressure, but if this engine is not getting required pressurization that may lead to the symptom he is seeing.