I assume you got this worked out. I can assure you, you didn't get a "dud". I am fairly confident you ran the engine too rich for too long and the sleeve is gummed up, and/or not properly seated....causing the piston to keep getting stuck. I base this off the fact I've owned/broken in 40+ engines and have had it happen to me. I've also seen it happen to others quite often. One major misnomer in this hobby is that it's safe to run an engine rich, when in my experience, it's more dangerous than to run it lean. I have conducted a lot of analysis on engines, and I have been unable to damage an engine running it too lean. Normally it cuts out..but never any damage.
Running too rich is a different story, in my experience.
Three tanks of idling is extreme. I'm unsure who instructed you to do that, but you there's your problem. It's not playing it safe, but instead a liability. I had to learn this the hard way. These are facts.
Consider this. You stated three tanks of idling, and 2 tanks of 'easy driving'. So you are five tanks in, correct?
So here, I am on
Tank #6:
(scroll to the 2:07 mark)
Years ago I saw someone break in their engine during one of the qualifiers at our track. I couldn't believe it. By the time the mains came around his engine got busy (this guy ended up being a factory drive for Agama, I believe) But this showed me something so I started learning and experiencing. I concluded that you can take and engine and have it broken in and ready for race tuning easily within 5 tanks. I personally go
I'm not saying my way is correct, just that it has worked extremely well for me. The times where I did "take my sweet time" the engine did just what yours did.
All is not lost however, it can be mitigated. It might not run as well as it could have, but in all candor I would just use that engine to learn on and once you cut your teeth to then upgrade as desired. I'll tell you now, this hobby is not for the feint of heart. It will make grown men cry. I see it on the weekly...people who used to run nitro come back and have problems galore. That;s just how nitro is. Stick with it and it will reward you, but if you half-step through it you'll actrually regress (as in I know guys whose vehicles/engines are actually worse than stock). :-)