Black smoke is a lack of sufficient air for the amount of fuel you apply to the cylinders or simply stated as "over fueling".... And it is caused by several different ways... one of which is indeed as In Chief engineers dump truck example..another is a clogged air filter.yet another as EX-Calif says bad injectors...in Chiefs example it is because the driver is starting off in too high of a gear
for the weight on-board there for lugging the engine with his foot mashed to the floor...take a peak in that cab and you will most likely find a young buck with his hat on backwards and all the air let out of his suspension seat so he is riding low and looking cool.....Shifting all day long is tiring..and if the truck will pull from a stop in 3rd they will use it and not 1st gear
as they should...that cuts off about a thousand shifts during the day.
You are basically doing the same thing by advancing your throttle to quickly as the propeller
grabs big bites of water
with little compensating forward motion through it...or in other words your lugging your engine too.,until the boat comes up to speed allowing the prop to increase speed which allows the engine to increase speed which finally in turn allows it to BREATH or suck in enough air for the amount of fuel your asking it to try and burn.
FWIW ,truly unburnt diesel
fuel is white out the exhaust
..a good sign of a bent rod as a mater of fact...why? no compression no fire.
We have little risk of this... but that truck driver can actually over fuel his engine enough to actually burn holes in his pistons..I have had to retrain every truck driver I have ever hired...most have a mentality of " It ain't my truck"...I made it their truck from day one.