My Farmall Super MTA has developed a 'popping' sound that appears to be coming from the air intake stack. It seems to have lost power and runs rough. A friend suggested that it might be a bad valve. If that's what it turns out to be, am I looking at a major repair on this M gas burner? Thanks Dick Dick Day Software Services 83712 552nd Avenue Norfolk, NE 68701 402/379-1606