Yours is a classic example of valve stem carbon deposits. I'd suggest the procedure I described about flooding the intake with penetrating oil and letting the engine sit overnight to soften the carbon deposits, then giving the engine a few hard full throttle runs and wind it up in the lower gears to blow the deposits away. As long as you don't go crazy on the RPM you're not going to hurt it. These engines were designed to run- - - -the way people pamper them these days, it's no wonder they get gunked up.

KROIL would be my first choice. Sea Foam is a good fuel tank additive, but it's not aggressive enough to dislodge a carbon buildup. www.KANOLABS.COM

Jerry

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