Re: So many brands of engine kits!
Welcome to the forum from Dallas Downhilly.
The best motor kits are Flying Horse. BikeBerry is a good place to buy them. Power King is another good brand, that you can buy from Pirate Cycle.
Another very popular brand is SkyHawk, but I haven't been very impressed with them.
Don't get suckered into a BGF (Boy Go Fast) on eBay by low prices. They're crap piles.
Try to get something with a NT carb, not the CNS.
Have fun, and I'm looking forward to seeing your build.