I got this R/C airplane engine used and had some trouble finding a copy of the manual. I don’t even remember where I found it now, but here it is for anyone else who needs it.
The Enya 53-4C is legendary for power-to-weight ratio. I haven’t flown this engine much (and I’m now rebuilding it, slowly) but it seems like a real powerhouse.
Enya 53-4C Operating Instructions:
If you’re looking for parts, I believe MRC still carries them.