In four cycle operation, a typical two stroke engine will run rough and "burble". That's the best I can describe the sound. It makes a sorta low "burble". It spits a lot of unburned fuel and oil in the exhaust and will probably not transition well. It may miss a lot. DO NOT break in an ABC/N engine in this mode, you'll ruin it. The two cycle operation will sound smooth and accelerate fairly well. It will have that smooth whine you're used to hearing from other engines.

ABC/N engines need to be broken in at only a SLIGHTY rich two cycle. The reason is this. In ABC/N engines, the cylinder is ground with a slightly smaller diameter taper at the top. When the engine gets up to proper operating temperature, this taper expands and allows for the proper fit of the piston. If it doesn't get hot enough (and it won't in four stroke operation) the taper won't expand. The piston constantly pushes against the taper, and will quickly wear out the cylinder and piston.

Start your engine and adjust the needle valve until it just begins to run smoothly, at full throttle, with that high pitched whine. Let ut run about half a tank, maybe 4-6 ounces. Shut it off and let it cool. Repeat this several times. How do you know when it's broken in? When it will hold an idle for about 30 seconds and still accelerate smoothly, it's ready to fly. The remainder of the break in is done in the air. After this, you may adjust the needle for full power. How can you properly do this? Easy. At full throttle, briefly pinch the fuel supply line. If the engine sags immediately and dies, it's too lean. If it picks up speed and runs a while, it's too rich. If it picks up speed and then starts to die, it's right.

Dr.1