Since I don't consider the Cox and Testors rear-induction .049s real engines (but rather metal mosquitoes), my first one was an HB .40 PDP...

I learned a lot on it.

It was my only engine to ever shaft-run (wood prop not tightened firmly enough). The only one to ever break the crankshaft (hydraulic-lock and a starter...).

I also made the mistake of soldering an extension for the needle, with the O-ring inside it (old Perry carburettor - the high-speed needle never could hold its settings). I also made it run too lean and need a new ring...

But it was a screamer!
Friends with Webra Speed, Enya and OS FSR engines of the same displacement were amazed [X(] at its abilities.