Bill, If your car has a weak valve, and you repeatedly decline to fix that problem - most mechanics will write you off when you have any further driveability complaints. When you have a burnt valve, monkeying with the fuel mixture will many times bring about a slight temporary improvement in the "feel" of how it runs. If the car has a burnt valve, you are wasting the time of you and your mechanic by even considering looking into other driveability problems. You test until you find a problem, fix the problem, then retest - especially with mechanical conditions. If you don't trust the mechanic, leave him alone and find one that you do trust. Good luck Bill, Jeff Ruffing 65 Imperial Crown Convertible ASE Master Auto Tech L1 Advanced Driveability Certified Tech