Faults:

The two-stroke engine is very sensitive to the condition of the spark plug. If it becomes fouled or dirty due to excess oil, there will be no spark.

If the bike has been parked for a long time, fuel residue can clog the jets (fuel dispensers).

An incorrect oil mixture can cause piston seizure or jamming, while using too much can foul the spark plug.

Being an old two-stroke engine, if the ignition timing is too advanced or the engine overheats, it may start in reverse when started.

Over the years, the piston rings (segments) wear out or stick to the piston due to lack of lubrication.

General Comments:

How to begin describing this beautiful motorcycle?.

Its manufacturer was known in Germany for also producing vehicles with two-stroke engines (some of which we've even seen in the US, both back in the day and some even now as classic cars). While their motorcycles were less well-known, they did make some, and in particular, this model, the RT 125, marked an era, as many other manufacturers wanted to imitate its design (in fact, if you look at it, it seems like you're talking about a post-war Harley Davidson).

This model is equipped with a 123cc, single-cylinder (inclined), two-stroke, air-cooled engine; with a three-speed gearbox. It achieves a power of 5.6 hp and a speed of 52 mph, for the machine's weight of 209 pounds; it also had low fuel consumption.

The design of the DKW RT 125 is as simple as it is brilliant. Even after countless years, it remains a very enjoyable motorcycle to ride, as well as being comfortable, with an optimal riding position, very good for the open road.

Being a very old bike, it's clear that it requires a lot of maintenance, but with proper care, it's a bike that doesn't give you any problems thanks to its simple mechanics and efficient engine. I bought it in very good condition and with low mileage, but in the time I've had it, I can say that I've used it quite a lot, and it hasn't given me any problems beyond the basics.

But besides all this, what's most valued in a bike like this is its ride. The melody of the engine's sound is something that no modern motorcycle can replicate, which is why these bikes, except in cases of extreme necessity, won't be sold.