I am currently restoring a Partner 22 GBI leaf blower and facing some weird issues. I have removed the carb, cleaned it in the ultrasonic and restored everything to factory settings.
After running some tests today I am facing the following behavior. The engine starts even without choking it after 1 or 2 pulls, so I guess it gets a good amount of fuel. The engine will then idle, but the speed it idles is different on almost every start. After a couple of seconds idle RPM becomes very unstable. It revs up, starts dying down, then idle on a really really low RPM for a second or two where you'd think it will die now, then it recovers to a more or less stable RPM again for a couple of seconds before starting to surge again.
Now the weird thing is that these fluctuations are not really rhythmic but completely random (sometimes it runs fine for 10 seconds, sometimes for 2 seconds) so it does not seem like there is a bad feedback cycle. Eventually a surge happens, it slows down and then dies. Ususally the engin runs for 20-40 seconds before randomly dying down.
What am I looking at here? I am really confused, no adjustment of the mixture screw (it has no high speed needle) really did any meaningful change to the behavior above...