In my earlier post, I said I had experience only with the Honda GX35. That was a true statement as far as the Japanese engines. And that particular Honda is actually manufactured in Thailand. I have also useed a 50cc, 2 cycle engine from Harbor Freight's auger. I started with the auger engine because I already had a brand new one, still in the box, before I got interested in motorized bicycles and before I accidentally found this forum.
I've used both engines on my BMP friction drive set up with no problems with either engine or the drive system. Depending on who you want to believe, the Chinese made 50cc 2 cycle engine from the HF auger, it's reported to be 50cc w/1.5 HP or 52cc w/either 2 or 2.2 HP. The Honda is consistently reported to be 35cc w/1.6 HP.
The 2 stroker Chinese engine is definitely more powerful. As I said earlier, ½ HP makes a big difference on these small engines. But I do like the simplicity of the Honda 4 stroke (no mixing of fuel & oil), and it's a little bit quieter and doesn't smoke like a typical 2 stroke.
All the stuff I've read about engine location, like Staton's new axle mount being quieter because the engine is further away from your ears, I think is just a bunch of hype. Do you think a foot (if that much) in distance is really going to make a difference ?
As 5-7 mentioned, BMP has a great deal on their friction drive set up right now. I know he knows a lot more about this motorized bike stuff than I do, but I'd be very reluctant to put any engine less than 1.5 HP on one ! Of course, that depends on personal preference and total weight of bike and rider along with the type of terrain you'll be riding on.
In case you don't know this, go to BMP's site and click on the link referring to engines and you'll find several vendors listed for both Japanese and China engines. I don't remember the exact amount, but I think I paid about $200.00 or $220.00 for my Honda including shipping. I actually wanted a Robin/Subaru engine but couldn't find a good enough deal on one when I bought the Honda.
Anyway, for around $350.00 +/- a few dollars, if you want a friction drive kit from BMP, you should be able to get their kit and a descent dependable engine that should last for a long time and many miles.