i have the same sprocket size, im 230+ lbs and my bike had trouble before i did what i mentioned above. now it makes it up going what im guessing is close to 15mph no pedaling.
try the stuff out that i said, get some gasket paper (5 bucks) and cut them to match the port on the engine, if you have a dremel check out this thread: http://motorbicycling.com/f13/basic-...olz-16646.html
the plug and wire are available from SBP, <20 bucks shipped and it is a very noticeable difference
plug: Sick Bike Parts
wire: Sick Bike Parts
any local bike shop will be able to repack/replace your bearings, usually for around 10 bucks. and im not sure what tires you have on there but anything smooth will work nicely. and new ones will cost you around (30 bucks)
also, grease the gears inside the clutch cover lightly and make sure your chain is lubed well. any auto grease will be better than nothing (5 bucks)
everything ive described will make it a brand new bike and all for ~70 bucks (30 if your wheels are in good order) that motor with that sprocket should def be able to move you up a hill when its cleaned up