Is the 'compression tester' used here of the type which connects in place of a spark plug? If so, I presume it is necessary for the engine to be 'turned over' (through top-dead-centre) to obtain the reading
.
If the above is true, it should only give a meaningful (maximum) reading once the exhaust port is closed. Therefore, it shouldn't matter whether the carbs or exhausts are fitted or not. Also, the condition of the power valve seals should not affect the reading. It would also appear that a two-stroke engine's secondary compression ratio would affect the reading, limiting the ability to compare readings from one engine to another.
Although I may have the wrong end of the stick, this device only seems (possibly) useful for a basic check of the piston rings and cylinder-to-head seal (gasket, o-rings etc.). For the readings to be of much use, one would have to know a baseline setting for a near identical engine in 'new' condition and also be aware of a minimum figure below which the engine will definitely require reconditioning.
I envisage that one could recondition an engine and then use a compression tester throughout the same engine's life to keep an eye on ring wear and leaks, but factors such as temperature (as alluded to already) and oil residue in the bore must surely affect the readings
.
I have never used one of these devices, so perhaps I have missed the point
. If so, I'm open to someone setting me straight!
Thanks & regards,
James