T25 only running on 3

[937carrera]

I saw that but the picture was too dark for me to see the absent nut.

Nice easy fix then

[Mr Bean]

I am puzzled as to how the compression test didn't give more of a clue particularly as we already knew which pot was in trouble.

[937carrera]

Both valves closed, "sealed"container with piston moving up and down compresses and decompresses the air from atmospheric pressure

[Mr Bean]

OK so thinking on - maybe as in some early configurations of engine development I can see that the valve/s could be opened by the "vacuum" created as the piston approached BDC. One way or the other the cylinder/combustion chamber would need a complete charge of air to achieve the correct compression value. Or as Mrs Bean often remarks, maybe I am overthinking the issue .