Thanks for the info- I'll try that. I've bled the lines and run the engine to pull everything out of the system in case something was stuck or had some kind of pressure/vapor lock. It really seems like it is fuel-starved rather than rich. As I said, it seems that something fills up with propane if it sits for a period. Could a backfire rupture the diaphragm in the carb or change the mixture setting? I haven't re-set the timing since I played with it, but it runs ok for the short period that it runs... could bad timing create a low vacuum that keeps the lockoff from operating? I'm not near it right now, but if I recall the lockoff vacuum line goes to a fitting on the back of the water pump. There is another line close to it that runs to the carb, and that line is atached to a fitting that is in a raised area of the valve cover. Is that a PCV type of unit...or maybe something that regulates pressure to the lockoff valve?