I'll bet you Ten zillion space bucks these motors don't get broken in properly at the factory. I'd even wonder if they get them up to operating temp.
This is a break in method used by race motor builders. It seats the rings and gets everything heated up and honky-dory.
+++ NEVER RUN THE MOTOR WIDE OPEN WITH NO LOAD!!! You can hurt your engine and yourself!!! +++
Once you get it back together and put the proper amount of oil in it, hook everything up, axle, chain, and all.
1) Run it for 15 mins with the rear end off the ground (Ferris Bueller style) at about 2500 rpm, give or take. If your clutch seems like it's running hot, bump the rpm up a tiny bit. (I use vice grips on my throttle rod to hold it at a steady rpm so I can do other stuff, cause man is it boring!!)
2) Let it cool for 20 mins.
3) Run it for 15 mins with the rear end off the ground at about 2500 rpm, give or take.
4) Let it cool for 20 mins.
5) Run it for 15 mins with the rear end off the ground at about 2500 rpm, give or take, but this time vary the rpms a little during this cycle. (Don't rev the pi$$ out of it though.)
6) Let it cool for 20 mins.
7) Drain and refill your oil with some fresh stuff.
8) Go for a ride, but take it easy the first 5-10 minutes. (NO full throttle just yet)
9) After that, let er rip!!!!!!!!!!!!
10) It is recommended that you change your oil again after your first 'spirited' ride. After that, change at regular intervals.
This concludes motor break-in 101.