Hello Tim, I do believe there is a pot that controls burn-back(I also think that it is labeled as burn-back) that is located under the sheetmetal on the 251 on one of it's boards and the 22A as well. Before you go to tearing things apart though, you might want to try to call Miller directly. I believe they have their assembly lines going on saturdays and possibly one of the line techs could help to answer your question. I do have a number that came off of their website, 1-920-734-9821, I don't know for sure that anyone will answer, but it might be worth a try. Good luck and regards, Allan