Carbon Carbon Carbon (on GP's)

[jt20]

After doing a series of compression tests with my crappy HF model comp tester, I am repeatedly surprised by the amount carbon that has built up on them after just a short run (5-10 min or a 1/2 mile city).

I know they are in the PC and diesel is shot right past them then burnt very quickly, but does this build up over time? How much is normal?

the car does alot of sitting, there was a bacterial infection recently but Startron cured that and it is still in the tank.

compression results hover just under 400 psi across the board.

I also dropped one!! How resilient are they (Bosch France model)?