Bill, sorry to hear this. The 228 I had 40 or so years ago was doing the same thing. It turned out the whole back side of the number 6 cylinder was full of old junk. Couldn't see of course but I suspect it may have been a couple of inches deep. Since I didn't want to pull the engine I drained all the coolant, removed the water pump and made a long tool out of a coat hanger. Just straightened it and bent sort of an L shape at the end. Then I worked it all the way back to the rear and jerked it back and forth and twisted it around to dislodge as much of the crud as possible. I tell you about this to save you the trouble.
Then frustrated that wasn't working as well as I hoped I got one of the cheap spring-like plumbing snakes and I worked it in and back there. It was the one that had a spring diameter of about 1/4"...not the heavier 1/2 or 5/8" one the plumbers use. It was much more effective at twirling around and it broke up much more junk in the process. Still wasn't easy, however. I was at an angle and flushing with a garden hose out the water pump opening. I did this for most of an afternoon and then I jacked it up so it would lean backwards and poured some stuff I got at the auto parts store (which was sold as rust dissolver) in there and let it sit for a couple of days. Then I got the plumbing snake and repeated all that action I mentioned earlier. After that it ran normally again.
When I had this same problem with my 235 about 6 years ago I did the same thing but I didn't have that plumbing snake any longer so I poured CLR straight in there and let it sit for 2 days. Drained it out, neutralized with soda and repeated two more times. Finally I was able to break up enough to get it flushed out okay. Good luck.
