ORIGINAL: bigedmustafa

I own a JBA .56. It wasn't particularly hard to break in.

Use an 11x5 or 11x6 2-bladed prop for your first few tanks. Remember that APC props are heavier than most other brands, and they may not be the ideal prop to use for break-in unless you go an extra size lower in diameter or pitch. This will allow the engine to rev up comfortably without overloading it. Once the engine is broken in, you can try a heaver loading prop like 11x7, 12x5, or 12x6. You'll want to use lower nitro fuel (5% to 10%) during the break-in period; you can try 15% nitro after the engine has 3 or 4 tanks through it.

Tune the high speed needle so you can find peek rpms at wide open throttle, then turn it back about 1/2 turn counterclockwise to richen it back up. Run the engine with the high speed needle set to that 1/2 turn rich-of-peek setting on the ground for a tank or two. You don't want to run it very rich, the engine needs to heat up so the piston liner can expand. While running the engine on the ground, if you have ear protection, you can alternate the high speed needle from 1/2 turn rich of peek to 1/4 rich of peek then back to 1/2 turn rich of peek again. You want to alternate the high speed needle every ten to fifteen seconds. This will let the engine heat up properly without getting overly taxed. If you don't have ear protection, just leave the engine at the 1/2 turn rich of peek setting then walk away while it burns through a whole tank of fuel at wide open throttle. The engine will break in more quickly if you alternate the needle as described, but it isn't worth damaging your hearing.

After two tanks of fuel run through it at wide open throttle, you can try to set the low speed needle to provide a reliable idle. You want the rpms at idle to be low enough that your plane won't roll on pavement under it's own power, but not so low that the engine bogs down and dies while it's sitting at idle. To get your low speed needle set properly, use the ''pinch'' test.

The pinch test involves leaving the engine at idle speed and pinching the line to the carburetor. If your low speed needle is set correctly, the engine will rev up notably for a second or two and then start to sputter and die. If the engine continues to run and run at the same speed after you pinch the carburetor line shut at idle, your low speed needle is too rich. Turn the low speed needle clockwise an eighth of a turn to lean out the low speed needle, then try the pinch test again. If you pinch the carburetor line shut while the engine is idling and the engine dies almost immediately without speeding up a bit first, your low speed needle is too lean. Turn the low speed needle counterclockwise an eighth of a turn to richen the low speed needle, then try the pinch test again. Continue adjusting the low speed needle in small increments until you get the brief rev up then sputtering and dying previously described.

After about three tanks of fuel, you've run the engine for two full tanks at nearly wide open throttle and then adjusted the low speed needle to get a good low rpm reliable idle. You're now ready to fly.

Fly the engine at that 1/2 turn rich of peek setting you originally started breaking it in with. The prop will unload and the engine will turn faster in flight than it does on the ground. Flying at 1/2 turn rich of peek will keep the engine from peeking even after unloading a bit during flight. After flying three or four more tanks in the air like this, you can begin adjusting the high speed needle back toward 1/4 turn rich of peek for more power. The engine will be very well broken in after this and you should only have to make minor adjustments as weather conditions change.

Feel free to ask any additional questions if any part of this ABC break-in procedure seems unclear. This technique will work well for most any ABC engine, I've only specified prop ranges with regard to the JBA .56.

Good luck and good flying.