To ream the cylinders, begin by coating the blades of the reamer with some sort of oil like automatic transmission fluid or gear oil. This will help the reamer pick up and pull out the excess carbon.

Now push the reamer in to the cylinder gently while turning it. Thread it by hand as far as you can in to the pre-chamber hole. Then, use a 12mm wrench to continue to thread it. You'll feel resistance come and go as it carves out the carbon.

Insert the reamer until it stops turning against the head, then back it out. Clean it between cylinders with some brake cleaner.