Today I changed Gaptooth's sparkplugs and was
shocked to find that the plugs were
LOOSE. I don't mean that they weren't torqued down sufficiently, but rather, plugs 1 and 2 were backed out possibly several full turns, and 3 was only just snug. Plug 2's hole was full of soot, and both 1 and 2 had oil well up the threads.
After putting in new plugs and torquing them down properly, I took Gaptooth out for a test drive and actually shouted in surprise the first time I put the pedal down, the power increase was so noticeable.
EDIT: For the record, my cylinders are all "B" indexed.