Bit late to this thread, but I also agree that De-carbon and Oil Consumption increase is a Myth. Carbon is a danger to your engine in several ways.
Here is an example on the Engine I purchased as a replacement and found this....All caused by Carbon breaking off around the exhaust valve and it stalled the piston on the upstroke damaging the top edge-
Needless to say I had to fully re-bore and rebuild this one, but the Carbon was mountainous around the Exhaust Valve and must have been glowing when the engine was running.
I always find pre-soaking the carbon deposits to loosen then off works well and only needs a piece of blade shaped wood to clean it all off.
If you can get it like this, it's well worth doing and will run nice afterwards-
Richard. ........ A Conscientious Financial Contributor to Redsquare enjoying the benefits of being a Supporter
1972 Raider 12. 1-0311 ser 123172. WH spec Refurbed. 36" RD Deck awaiting refurb.
1974 C-120 1-0353 ser 137717 Rebuilt/Cobbled worker Rear Cultivator/Harrow.
Cyclone Seeder 93a. awaiting refurb http://s1190.photobu.../AngloTraction/