Our GE 44 Ton locomotive has two 40's vintage Cat d17000 v-8 deseasels in it.
Most of it's time is spent idling around the yard, one or two cars, a quick jolt of power to get things moving.
Had to bring a two heavyweight passenger cars up the hill from the other end of the line.
Wide open, down to about 10 mph, the stacks starting blowing like the steam engines, black smoke, red embers, even some flames out the top of the pipes. Took a good 3 or 4 minutes of running before it cleaned up. Fortunatly it had just rained and everything was sopping wet.
In that case though, the wet stacking is because they are worn out
Another issue with the standby gennies, would be the length of the exhaust system. A short pipe would be less prone than a long one. The raw fuel condenses in the cool portions of a long pipe and drains back.
Our gensets here at the railroad use oil cooled engines, and they seem to warm up quicker and are less prone to piddling all over themselves.