don't let the"non brand" thing fool you.
the majority of these chinese engines are identical, and thry all use the same parts.
My $125.00 "e-bay special "66 c.c. runs better and is faster my buddies $250.00 brand name engine, and actually mine is mechanically quieter than his is. with me on my bike, i can top out at 32 mph . with me on his bike, i can top out at 26 mph. both bikes are set up the same, (same wheel & tire sizes, same size rear sprockets, same size frames, ngk spark plugs and better plug wires. both have modified exhausts and high flow air filters.)
I have an $114.00 50 c.c. "e-bay special" that actually pulls away from my buddies $250.00 66 c.c.. top speed of my 50 cc is around 28-30 mph with a 41 tooth rear sprocket on 20 inch wheels. it has an expansion chamber, better spark plug wire, spark plug, and a high flow air filter.
as long as you tune it, maintain it, break it in right, and always run the correct fuel-oil ratio, your non branded engine will be fine.
you will want to upgrade the nuts, bolts and washers to better ones. use blue loc-tite on everything, and take your time mounting the engine on the frame. check everything 3-4 times to make sure everything is aligned right. solder all wire connections together and heat shrink them.
tie your wires to the frame with plastic wire-ties..
take your time building your bike and you will be much happier in the end.
do as much reading as possible and find out as much info as you can.
educate yourself on 2-strokes, and how to build one of these bikes.
please don't be one of those people who throws the engine on out of the box in one day and expect it to be perfect.
you will find taht you will probably have to modify a few things, tweak a few things, and replace a few things while you build your bike to get it right.