Then it's a good one. These engines last a long time and it's the only stock water-cooled motor I've heard of. It has a static sleeve around the cylinder of which you fill with water and anti-freeze. Usually, it only needs to be filled maybe once a year or even once every 2-3 years. If you get the moped, I'll be more than happy to give you more specs on the ratio and the location of where to put the water/antifreeze mixture in.
Just a note, these engines have a lot of compression and is stronger than most moped engines. (2.6 hp, 49cc) So, you'd be better off pedalling the moped like a bicycle on the road, off the kickstand and press on the clutch to get it started, rather than start it on the kickstand. Much easier and you don't kill your kickstand.
My motor starts up usually in just 3-7 feet of pedalling in distance, which is pretty good. I know of a source where you can get a NOS brand new never fired Solo engine for approximately 125.00 shipped to your door. It also includes carb, exhaust. Amazing deal.
The Columbia mopeds were also known as Montgomery Ward, Columbia, and KKM. The moped was originally made by Columbia, and the engine came from Germany. Later, Montgomery Ward bought it out and slapped their sticker on it. Later, KKM bought it and called it "KKM Mopet" (yes, with a T. I don't know why)
Parts are very easy to come by at Handy Bikes and the prices are pretty reasonable. Although, stay away from their accessory switch. Most of them are cracked. Everything else is excellent.
KKM recently, about a year or two ago, went out of business, so Handy Bikes probably bought up a large chunk of KKM as well as this other guy, Steve Tietjen, of whom bought out a lot of Solo Engines.
It seems that there are only a few people that knows anything about them, and I'm one of them. If you bought that moped, keep in touch, I'll be glad to help out a fellow Columbia owner.