Old guy here having years of experience with both bicycles and motorcycles but I am entirely new to motorized bicycles, as my new adventure. Basically, I am in the low speed camp, not interested in seeing how fast I could get a bicycle to go. In the region where I live there are smaller rivers running north to south with several miles of distance between the rivers and the roads following alongside those rivers tend to not have any notable hills but the east and west roads include some big hills in between those rivers and so a bicycle having a small engine needs to be geared down for the torque needed to climb those hills. Plus, I plan to include a pair of wire baskets on the back of the bike for grocery shopping trips, so the bicycle I am working on could be considered to be a two wheeled SUV. With the right gearing, a Honda GX35 engine seems just about right.