Just an update...
I think this is a fuel delivery issue as it got the revs to drop by manual pumping of the primer bulb.
I ran it over the weekend with a full tank, ran fine till it got to the point where the fuel is in line with the top of the fuel filter, then it leans out and stops. I removed the fuel cap and it still did the same thing.
I manually checked all lines, decompression valve, diaphragm, etc. All clear and working fine.
I'm thinking it's the fuel filter? I'll replace with a new "non eBay" unit and provide an update.
Any thoughts?
