Well this is a new one for me. I went to fly my Shoestring. Regular run up was okay and did not notice anything until I got in the air and it was really bad, so I landed and readjusted again and changed the plug. Went on up and a repeat performance. Now keep in mind this is my regular baby which I fly more than any other plane. I don't believe its out of adjustment.

While at an idle, the RPMs go up and down, not much but enough to notice. I am going to strip it down in the morning to take a peak and hopefully find something obvious in the tank or lines. Even break down the carb. Right now it's a mystery. Any ideas here? Thanks