The piston was installed backwards. The long skirt goes toward the exhaust port. My idle problem and lower power readings are cured. With the piston installed 180 degreese (incorrectly) the intake and exhaust ports are momentarilly open or bridged thus injecting some exhaust gases into the crankcase and diluting the fuel air mix. I have picked up 400 rpm top end and can idle at 1900 to 2100 rpm reliably now. Thanks to all for your info and making me dig.