This is how I break in my engines.
My engines are faster and last longer as other people's engines.


First you have to start with acquiring some pure castor oil, I got mine from a go-kart shop, most of the time the go-kart guys only use high quality oils.

I would recommend using a castor based fuel, like Runnertime and Capricorn fuel.
Don't know if these are available in the US, maybe some US drivers can recommend some good caster based fuels.

Add 10% of the castor oil to the first liter of fuel you are going to use for break in.
Warm up the engine till 80C, takes about 15-20 minutes with a hairdryer. Don't use a heatgun, this will only heat the outside and not the liner.

Open up the high speed needle about 1.5-2 turns from factory settings for the first 4-5 tanks on the starterbox.
These 4-5 tanks will be at WOT, the wheels shouldn't start turning at this stage, but close to the point they will start turning.

After these first tanks of fuel let the engine completely cool down and close the HSN about 1 turn, just enough so the car is able to move around the track but doesn't start shifting, engine temperature needs to be around 75C.
Let the engine cool down every two tanks to let all the parts settle.
With this setting burn the remaining part of the 1 liter of fuel with the 10% extra oil.
When you completely burned the 1 liter of fuel prepare another liter but then with 5% extra castor oil.
The first 5 tanks of the 5% extra oil fuel you will need to run the engine at 90C and the car will probably start shifting regularly.
I always loosen the 2-speed a quarter of a turn for break in.

After the 5 tanks you can start tuning for performance but still with the extra oil.
After you have gone through the second liter, let the engine cool down and check if the piston is still tight in the liner, if so run it a couple more tanks till the piston isn't tight, doesn't stick in the liner.
It took me 4 more tanks to get the tightness out of the liner, again with the 5% extra castor oil.

Because of the extra oil the fit of the piston inside the liner will be much better and the liner will receive a much smoother polishing which results in more revs and less wear compared to tuning an engine for max performance while the piston is still tight.