I have heard of the water Steve and I have also heard using transmission fluid.??? I have read the threads on GM's EOS.
Used it in the past with good results. Talked to a parts guy at a Chevy dealer and he told me GM changed the formula in the EOS and doesn't recommend it in older flat tappet cammed engines. I bought the last two cans he had under the old part number.
The G.M. cleaner is now called upper engine cleaner, clear plastic jug, blue stuff. Old stuff in metal can was called top engine cleaner, both used via intake (engine running, pour into carb, feed into vacuum port, etc.)or removing plugs to soaking piston rings.
For trying to remove old, hard carbon I'd try water first, in addition to cheap the water vapor is less likely to get the fire departments attention than the cloud of nasty blue fog of the good 'ol Top engine cleaner produced.
Note: Use caution when adding any liquid to the intake of a running engine, rods will bend!
The GM EOS (engine oil supplement) is thick, not the stuff to add to the fuel system. There was GM camshaft prelube (small clear plastic bottle) but my parts manager seems to think it's been discontinued. May have been, haven't been anything with flat tappets for awhile.
