Although there is no consensus as to the right way to break in a new cylinder kit, the following is a series of steps one might use to break in a new cylinder kit.
First, a few notes on break-in from Graham Motzing:
the idea is to 'seat' the rings. they come a little bit rough from the factory, and the cross-hatching on your cylinder is a bit rough, so you want to let the rings hone themselves into perfect alignment in the cylinder. Its very important, and even a lot of people who dont have massive failures, do have some ring blow by that reduces performance.
the key idea is high pressures with low velocities. keep the throttle open with high load, you dont want to let it rev all the way out, but 1-2 hours worth of riding, alternating between full throttle to heat it up and closed throttle to slow down is good.
i used to have my shop on a big long hill, i'd go up the hill full throttle and coast down, about 8 times, then hand the bike off to the lucky customer and cross my fingers.
you should have your jetting almost right, if your bike is running like shit it wont make enough pressure to seat the rings and you'll start building up carbon on the sides of the piston, you should also have your timing about as dead-nuts as possible. most people who sieze their shit out of the box have their timing wrong and think misfiring is 'four stroking' and they are too rich. downjet a couple sizes and blamo, siezercize. Dont be that guy.
Now, the procedure:
Step one: Start your engine, let it idle, and check for air leaks. When no air leaks remain, go to step two.
Step two: Start your engine and let it idle, occasionally blipping the throttle for four to five minutes. Allow the engine tocool completely. Repeat this heat cycle process four more times.
Step three: Warm up the engine again and ride the bike for five to seven minutes at a very easy pace. Vary the RPM, and do not ride at one speed. Do not ride at more that 1/3 throttle or more than 1/3 rpm. Let the engine cool down completely and repeat this initial break in ride. Let the engine cool down.
Step four: Check the head nuts for proper torque.
Step five: Ride the bike for five to ten minutes at a moderate pace. Vary the RPMs, and do not ride at more than 3/4 throttle or more than 3/4 RPM. Then let the engine cool completely and repeat this secondary break-in twice more.
Step six: Replace the spark plug with a new one. Ride the bike for five to eight minutes at a moderate pace. Vary the RPM. Once the engine is up to operating temperature, you can make a jetting pass. Ride at a moderate/high RPM. With the throttle wide open, hold the kill button down and stop.
Step seven: Read the spark plug. With a pocket flashlight and a magnifying glass, look at the porcelain part of the plug only. As you view the plug from the center electrode, look down on the length of the porcelain to its base. There should be a dark chocolate colored smoke ring. There was not sufficient time to thoroughly color the whole plug, so the nose of the insulator may still be white. As long as there is a visible dark ring at the base, everything is OK. Remember, we want break-in jetting, so the plug should read rich/dark. Richen the jetting as necessary. If you are having a hard time reading the spark plug, follow the proceeding steps: Put the plug in a vice, and hacksaw around the plug at the washer. Break the threads off with vise grips and the porcelain will be easy to read.
Step eight: Complete the break-in by riding at an aggressive pace for fifteen minutes. Vary the RPM and do not cruise at part throttle. Ride hard without revving the engine too high. At the end of this final break-in session do another jetting pass/plug chop as described above. Check the spark plug for the correct dark/rich condition.
Step nine: Replace the spark plug with a new one. Ride the bike aggressively for eight minutes and do a jetting pass/plug chop at full RPM. the porcelain color is still dark/rich, lean the main jet size one at a time until the smoke ring at the base of the porcelain is a light brown. If the porcelain base is white, do not run the engine, check for air leaks, and jet size. If the plug color looks good, continue riding at a race pace for ten minutes. Stop and let the engine cool. Check the torque on the cylinder base and head nuts.