Tech.
Steamcleaning pistons and valves:
This is a trick they used to do back in the old days, and IT WORKS!
if possible disconnect the exhaust.
you dont need to, but 1 its fun to see what comes out of there! and 2 crud won't stay in your exhaust pipe.
start up the engine and let it warm up, take the airfilter off.
fill a spray bottle with plain water.
start the car up again
spray just over, not directly into, the top of the carburator and at the same time
rev the engine up in a short burst.
the mist of water will be sucked into the combustion chamber where it instantly
will be transformed to steam which knocks the crud on cilinderheads and valves off
repeat this several times and you will be amazed of how much comes off of your valves and pistons.