Dave,
Thanks for that clarification. I've been running O.S. 4-stokes for many years and have recently experienced this very same problem. It occured after changng out a crappy ARF tank on my AeroWorks Extra 260, running a well broken in O.S. 81a. I'm going through the very same "re-needling" to bring it's performance back to where it was. I went from a 15 oz. tank to an 8 oz. one and suspect that that may have caused the change. I've been following this thread with great interest. I'll let you know how mine develops after this Monday. Checked all the usual things, plug, fuel filter, tank and lines, valves. I'll check back in on Monday.
Karl