I was 10 years old and had trouble with the Cox 049 in my PT-19 control line airplane. Mine looked like this, but the wings were blue and the fuselage was yellow:
Here's the engine with glowplug and glowplug clip shown as well. What's not shown is the spring around the crankcase for spinning the prop. You wind it backwards and let go and the spring does the rest:
The battery was one of those huge 1.5 volt dry cells that surprisingly, never did last very long:
I used this fuel:
Sometimes I did get the "good stuff", which really didn't make difference that I could tell:
Starting wasn't easy until I discovered that the suggested needle valve adjustment for starting should have been 3.75 to 4 turns out, NOT 3.5.
It was primed by dribbling a little fuel over the cylinder so some would go in the ports. That would cause it to run for a second or two, but I had to richen the needle before it would keep running.
And it was an unnerving experience reaching in to lean the engine out once running. The propeller hurts. I once cut two fingers to the bone when doing that.
But it was that starting/tuning challenge along with the subsequent satisfying thrill of a tuned engine that keeps me with glow-engines and I leave the electric to others who enjoy pistonless RC.