I finally got the heat riser loosened up. I followed Thoroc's back and forth tapping advice and 2Carls advice that it was a build up of both rust and carbon. I used plenty of penetrating oil, which helped somewhat. Then I tried a carbon dissolver. I used PB Blasters LMT, (Lawn Mower Treatment), which claims to dissolve carbon build up on pistons & valves. 30 minutes later, a few more back and forth taps on the riser rod and it popped loose. Swings freely now. Thanks.
