DCC and smooth slow speed running
gimme30;
One of the many benefits of DCC is smooth operation at slow speeds. Usually, a good deal slower, and smoother, than with DC.
For you to have the slow speed starting, and running, problems you describe, on a DCC locomotive, is weird. Especially since the same problem exists on two locomotives.
Whether programing the starting speed will help, or not, I'll leave to the DCC "digital divas" one of which I definitely ain't!
I spent a lifetime troubleshooting electro-mechanical stuff for a living, and model trains as part of my hobby. But I retired before much of today's computerized equipment had been invented.
Now I like DCC, and I use DCC. But beyond understanding the general theory, what goes on inside my NCE Procab is largely a mystery to me. :smilie_auslachen:
You might post your question about reprogramming the starting speed on the "Technical Forum" section here. They have lots of digitally savvy folks there who should be able to answer it for you.
In terms of general troubleshooting, your "The DCC system might be causing this problem." theory makes sense. Either both your diesels have the same problem, or some common factor is affecting both of them. The DCC system, and track, are two common factors; and you've already checked the track pretty thoroughly.
Both locos having the same problem is possible, if somewhat unlikely. The likelihood factor would go up exponentially if both locos are older designs with three-pole motors, no flywheels, and too-high gear ratios. I go back in N-scale to the jurassic era, when such lousy runners were all that was available. Back then, we had "two-speed locomotives." (The two speeds were 120mph, and stop!
) Those old dogs jumped instantly from stop to full speed whenever you tried to run them.
Yet you say your diesel locos are quite new. Does that mean newly manufactured, or "new to you?" (a.k.a. used, e-bay wonders)
What brand are they? Do they have flywheels? What is the electrical path from the wheels up to the DCC decoder? Are there any metal contacts that might be dirty, or is the wheels-to-decoder connection hard-wired? How many poles do the motors have? You can determine the number of poles by looking at the "rotor," the spinning part of the motor. It should have groups of laminated metal plates separated by gaps, that all rotate around the motor shaft. Mark one of these metal plate groups and then slowly hand-turn the rotor. As you turn the rotor, first, it should turn easily with no binding. Second, count the number of plate groups. You should find either five, (good) or three,(bad). The plates may also be "skewed" where the individual plates in a given group are not aligned exactly with each other. Rather, they form a sort of "stair step" pattern with each plate slightly ahead of its neighbor. This "skewed armature" feature, is also a good thing.
NOTE: Clear, close-up, photos of the locomotives, with the body shells off, would be a great help in diagnosing the problem.
While your looking at the motor, check out the "commutator." This is a group of three, or five, copper plates with little gaps between them. Its mounted on one end of the shaft, within the motor. The two motor brushes rub on these plates. Are the copper plates clean and shiny? If not, use a pencil eraser to rub off any dirt. Be very careful in this area. There are some very, very, tiny wires soldered to tabs on each plate. You don't want to break one. Were any of these wires already broken? If so, the motr is basically toast, unless you can do some serious micro-surgery by soldering the broken wire back on. (Yeah right!
hwell
Finally, if you find you can't fix the problem, you might consider replacing the loco with a Kato brand diesel. They are excellent, super-smooth, runners, and have five-pole motors, dual flywheels, and sensible gearing. In my opinion, they are the best N-scale locos available.
Good luck;
Traction Fan :smilie_daumenpos: