NOTE it is important to inspect the engine before run in for debris, clean in parrafin oil , try not to use WD40 or acetone if you can...

OK so lets get down to how you run in an engine

1 Put fuel into tank , Pre heat engine with a hair dryer.
2 Start engine
3 Let it run for 30 seconds while you tune top end to just rich of clean tune
4 Pop it on the ground and play with it ( dont cane the crap out of it yet ok! )
5 Stop after approx 3 mins and cool with piston at BDC
Repeat steps 2, 4 and 5 for between 500 ml to a litre

Thats it !

Ok so why do we do this ? Simple ! the engine needs to produce heat to let the sleeve expand and the best way to do that is to put load on the engine. But why ?
Well if you immagine the top of the piston being cylindrical and the sleeve being tapered then whats the piston doing when the engine is running too cool ? its smashing or linishing its edges off at a far greater rate than desired. After the first 3 mins of run time the engine has done some 60,000 Revolutions.. now if its cold thats when youll do the most damage. Not to mention the lower bushing of the rod taking a pounding.