In partial defense here about cleaner sitting in the manifold and helping to clean things up, I would like to pass on some history.
The genisis of this whole "vacuum suck" method of cleaning up the intake manifold as well as intake ports, combustion chambers, and valves, goes back before fuel injection was common. The technique was to spray or pour "combustion chamber cleaner" down the carb throat with the engine running. You would increase the throttle opening enough to keep the engine running, but allow it to run a bit rough from "loading up". When you would get near the end of the container of cleaner, you would allow the engine to die from increasing the cleaner or decreasing the throttle or both. You would then allow the cleaner to soak for usually about 15 to 30 minutes and then start the engine and blow all that crap out. The cleaner used went in sort of like a foam, and tended to cling onto the sides of the manifold and ports.
I know of at least three products that were probably canned by the same supplier that were used in this manner. One was Rochester X-88, another was Ford Combustion Chamber Cleaner, and another was a Shell product. I'm sure that Mopar had one as well.
When I had an engine that seemed to have a burned valve, I would often run the cleaner through it before pulling the heads. Rarely, the cleaning would restore the compression, but more importantly, it was much easier to clean the heads once they were off as most of the carbon was cleaned out. If I didn't have the Ford cleaner available, I would use water or sometimes hot water mixed with equaly parts of ATF. The water and water ATF mix didn't clean as well, and it didn't do much for the areas outside the combustion chambers, but it still made a difference.
So you can laugh all you want about the "vacuum suck" method not being effective, but in my lifetime I've had too many engines apart that had just had a similar service. It saved a lot of labor time in cleaning things up. Roughly speaking it saved about an hour per head.
If you are not getting that result, perhaps we need to continue to look for a product that will soak in and do a better cleaning. The Ford stuff is still available, although it is hard to find as many dealers don't bother to stock it. Just from the name, I wonder if SeaFoam would do it.
