Re: +7 mph by fixxing poor quality on 66cc
First things first, nice job spotting all the 'always check' things when building a 2-stroker, it takes most people a few builds to find them.
What you haven't learned with your first build yet is all motor kits are not the same so you need to specify the exact year, make and model of the motor you refer to as not ALL these motors are 'poor quality'.
I only use Skyhawk motors and it only takes me 1/2 an hour to prep one.
I use an angle grinder on the outside of intake/exhaust flanges to flatten it and remove any weld that keeps the washers from sitting flat, use a rasp bit on my drill to clear out any crap on the port pipes insides, torque the head bolts, set the spark plug gap if not simply replace it with an Iridium one, and then pop the right side clutch cover to make sure the freewheel bearing is not dried hard and stuck.
If it's a 66cc with a CNS carb I also gasket seal the grove on the top to prevent air leaks there and let it cure over night.
As far as 'cracking the case' to inspect the main bearings on every new motor, well to me that is just silly for lack of better friendly term.
Suggesting a layman even pull the cylinder off is likely to leave them with problems they didn't have to start with, let alone cracking the case, though I usually pop the head off to reverse the orientation of the slat heads and inspect the gasket.
It's always nice to get a new experienced mechanic in here and you sound like a good one so welcome bud, just be mindful that a large portion of the audience here are just kids that don't even have decent tools let alone mechanical skills is all ;-}
So are you hooked on building more of these yet?
It still amazes me how far they can be taken so I just keep building them ;-}