Nose down is my favorite method. I have never had much trouble that way, yet I have had some form of trouble in any method and for the sake of space, I have used about any and all methods.
Using a filter is -- IMO -- a sure need for a clean-out if you have any more than a couple weeks. OTOH maybe that is what caused my same problem about a month or so ago.
Old Ringmaster, Fox 35, had hung nose-down for months. Took it in back yard and after about 10 laps, it went bonkers. Then after a few seconds it started fine, maybe 5-10 seconds it quit. Tried same with same results after a number of "Quick Fixes". Back to the barn and have not tried it out yet. That Fox is at least 40 years old and RM is some 20 years old.
My Fox 19, very old, model an old all wood wing fuse, etc. is about 29 years old. Made a few flights trying to give a nephew some time. He was doing very well until I let him solo. Bad landing but that engine was performing extremely well. Same fuel as the 35 was burning, or trying to burn. My Fox fuel is "adjusted" from my RC to less nitro and MORE oil, castor. Been very busy and many chores like climbing and taking off limbs from these darn sweet-gum trees around the place.
Hope you, MR. Paul, are having much better luck.
BTW Guys, don't forget about Ol' Hoss when the ballots for AMA office come out. I may be a RCer but there are a number of nice CL models on the work bench.