Switch from powerplus to synthetic car oil

Don't do it unless you take it apart and flush it out VERY good! They don't play well together. Also, if your going to do it be very carful which one you use. The automotive oils are not formulated for splash type oiling. A lot of people have found that out the hard way. Best of luck.
Interesting post from Red Line Oil on the old Bob's 4 cycle:

Just bought motor that was run on powerplus would it hurt it to switch to synthetic car oil

(?)... What is your primary point in doing so? If...if $$$'s, you will be taking 'some' risk, but....it's unlikely the world will end. Time will tell! (Myself....I wouldn't do it)