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

Air leak some where on the engine (back plate, around carb, etc...) or a hole in the fuel line.

Thanks, I came on line to check for ideas and I'm going to go strip it down in a few minutes.

Well so far I found some hairy fibers inside the high end needle valve. That could be it. Everything else loks good , so I'll run it up tomorrow and see how it is.