F935 engine trouble

[dlbcheckmate]

Hello, great site ! I have a John Deere F935 with a Yanmar Diesel engine. I rebuilt the engine (new pistons, bearings, rings, injectors, glow plugs ect) after it started ok, I ran it about 1/2 hour or so and it quit. I was able to restart it but it does not seem to have full power. When I crank the engine over to bleed the fuel system it will actually slow down or stop cranking when you tighten up the line it resumes cranking ? Any ideas ?