The fish pond looks a lot bigger than I thought it would be,that will keep you busy for a while.
Could be crank seals are bad on the old 2 strokes as the symptoms of leaking 2 stroke crank seals are a lean idle, a flat spot at low revs or an engine that will not rev out. In some cases, the motor will not idle at all.
Probably just easier and cheaper to grab another motor otherwise you would do a leak down test with the ports blocked off and 5psi in the spark plug hole for 5 minutes to make sure the pressure doesn't drop.
Some people say just leaving a 2 stroke motor unused for a few years will dry out the seals enough that they need replacing.
I've had 2 strokes do what you describe and had to keep pushing the primer to keep it running with the plastic float needle but after fitting another needle the motor worked fine ,always felt like the needle wasn't letting enough fuel in when I had to keep it running by pushing the primer but easy to see if it's a carby problem by spraying 2 stroke fuel into air intake when it's running.
If the motor won't rev out with out extra fuel or won't rev out at all then it looks like the seals are leaking, if it's not restricted on exhaust side and no other faults.
