Depending on how much you weigh and how steep the hills are, you may need a shift kit for an engine that small.
I'm 250 lbs. Where I live lots of 20%+ grade hills. The bike weighs 100 lbs uses 26 inch tires. The engine is a Robin Subaru 35. 4 stroke, 33 cc, 1.6 HP at 7000 rpm, 1.2 ft/lbs torque at 5000 rpm and 8000 max rpm. The 7 speed reduction range is 49.21-18.82:1.
Max climbing torque is 59 ft/lbs. I have to lightly pedal assist on 25% grades had heavily assist on 30% grades. From an old setup I used to use a 55:1 reduction I lightly assist at 30% grades. That would give me 66 ft/lbs.
The level ground speed is 28.8 mph at 7000 rpm. The downhill assist is 32.9 mph at 8000 rpm.
I hope this helps some. Knowing the rpm range will really help. You can order a tach fairly cheap on eBay.