I understand, things like this can get yer goat, as they say

I looked into the aircraft.cfg and there's no [SMOKESYSTEM]
Remember, you can always make one, and then put in the effects you want. just type it it exactly as you see it in my previous little note there, including brackets, and bingo, you now have one!
Just remember to ALWAYS ALWAYS ALWAYS make SURE you back up BEFORE you edit any file. I am not sure where that artifact is coming from, but there is a really neat little add-on, ENGINE EXHAUST SYSTEM PLUS Version 3, that can really help the look.
Hope that helps a tad...?
Pat☺