Thats sounds like the CS .049 engine, also named Brodak MkI?
If it is tight you are lucky
They were really poor in terms of quality, I have actually flown one of my .061 engines but it wasn't exactly straight from the box...
Here is a thread on the .061 RC version from that time;
http://www.rcuniverse.com/forum/1-2-...i-give-up.html
Here are a few things to check for:
- use a 6x3 prop or smaller
- use 25% all castor fuel
- the compression ratio is too high, I use 3-4 head shims on mine
- the conrod will rub
hard against the backplate, along the full length of the conrod (needs a spacer on the gudgeon pin to prevent this )