125 cc engine, 64" propeller 3 blade, 180 kg gross weight, will it climb? I'm a government teacher in school, currently I made an RC aircraft and flew it, now I'm working on a single engine light weight aircraft, I want to use a Honda CG 125 (single piston) engine, with 64" propeller 3 blade, engine RPMs are 3000, wings length is 29' feet and width is 4'6" approximately, and the length of aircraft is 20', empty weight of aircraft is 130 Kg, gross weight will be 250 Kg.

I want ask you: will this climb?
I found a google site that showed: Honda GC 125 - 124cc, 10.8 bhp, @ 9000 RPM. 

Seems to me it would be much less at 3000 RPM. Can you use pulley/belt system to achieve high engine RPM (smaller pulley) and lower prop RPM (larger pulley)?

The frontal area you provide:

wings length is 29' feet and width is 4'6" (54") approximately, 

sounds similar to a Cessna 150, which has a narrower cabin (just about two adult shoulder width, 38 inches), and that needed 100 HP to fly, coming from a 200 cubic inch engine.  It's overall weight was higher tho, 1600 lbs gross (in my 1971 model) vs the 250kG/552lb you provided. If the extra 16" of width is all in the cabin, that will be a lot of extra drag to overcome with that low horsepower engine.