Thanks for the tips guys.

I did manage to finally get it running, but not what I would say is up to the reputation of these YS engines. I'm pretty sure I had a leaking gasket somewhere. The fuel system holds pressure for at least overnight, and it starts very easily by hand. Here's what I have done thus far:

ALL new gaskets (YSE2020)
ALL new O-rings (YSE2090 I think) including the throttle barrel seal
ALL new regulator components (spring, plunger, and diaphragm)

Here is what it is now doing: Starts easily, runs up to max RPM (minus a couple hundred, as per the instructions), return to idle, everything is fine for a while. After about a minute of running at various throttle settings (flying), the needles (both high and low) become inconsistent, i.e. run it up once and all is well, run it up again and it wont clear itself out without leaning the high end a little more. Then, after getting it to run up ok a few times, it richens up again starting the whole process over. The high speed needle is not 'drifting', as it is in the same position as before adjustment as witnessed by the location of the set screw in the end of the needle. The low speed needle also seems to be somewhat un-responsive to changes (starting with the factory 1 1/2 turns out). Also, I observed fuel running out of the carb after shutting it down (remember, all NEW regulator compolnents). A catastrophic flutter problem on the last flight prevented me from further frustration, but the airframe has been repaired and is ready for more engine tuning. I'm looking for advice on what changes to make next.

I cannot find any good, specific instruction on how or why to adjust the regulator, other than to 'just set the screw flush with the body', which it is. Could this be an issue?

Thanks for the advice, and sorry for the novel, but I'm trying to give you fellas as much info. as I can.

-Tommy