Chemtool always gave me pause: the solvents are very aggressive and I worry about their effects on hoses, seals and other rubber or plastic parts. A quick (like 5 minute) flush might be OK, but I would certainly want that stuff out of my engine fast. A less aggressive solution to accumulated crud might be Gunk Motor Flush, which smells like it is more kerosene-based, not having that toluene/xylene aroma, and is designed for crud removal. Even Gunk wants it out of your engine within five minutes, and they tell you to NOT drive the car, apparently because of the effect on lubrication quality.
Somebody recently suggested pouring the Gunk down the flame trap into the breather box, which seemed like it led to a quick fix. I still like Don's suggestion to do it right: take it apart, clean it out, and reassemble.