I did read the thread, and would like to add this. I don't have the experience of some of the others, but I DO have a GX35 that I have been running at full throttle for at least 70% of the over 200 hours on it, with ZERO problems. Here is why I think I have been so lucky.
1. I chose an engine with forced air cooling
2. I chose a highly reputed engine
3. I kept the air filter cleaned and have changed out synthetic oil every 25-30 hours.
4. My Nuvinci 171 Developer's kit keeps my engine in the rpm range at or above peak torque at all times while under load, (except for between 0-3 m/h) and I limit max r/m to the Honda 8000, by backing off appropriately.
My bike is an extreme example of low power/weight doing the trick, but noteworthy. It's a recumbent tandem, geared so 2 of us can climb an 18-20% grade, at ~3.5 m/h. So, personally, staying below 50cc is worth it, and can serve you well at your weight. I'm not looking over my shoulder, and I can throw my ride in the back of my truck and use it when we travel from Missouri to California to visit the blessed grand daughter. I know many folks (including my bro) have been successfully cheating cc prosecution for years, but I don't need that stress. For me, a high high/low range transmission, with low power but stump puller sprocketing is the right combo, and is more definably a "motorized bicycle".
