> Water injection is a very good remedy for "blasting" carbon build-up within
> cylinders. That used to be a popular add on system to prevent pinging before
> the advent of knock sensors and electronic ignition. I've heard a number of
> people comment that when they removed a head for a broken head gasket that
> the cylinder(s) that were adjacent to the break were very clean while the
> other cylinders had the usual carbon build-up. I've also heard you can
> dribble a garden hose into the carb. while the engine is idling and this will
> have a similar effect. You shoud probably change the oil after this, however.
> Greg Donati
My brother-in-law recommended using a glass of water and dribbling it in
slowly. Claims it works. His background is an owner of an auto parts
and been working on cars for 30 years. I have never tried it, so YMMV.