I would say it's definitely in the model. My reasoning:

If you change this the aircraft.cfg from this
[fltsim.1]
title=CS C130Extra2 1
sim=C130
model=10

to this
[fltsim.1]
title=CS C130Extra2 1
sim=C130
model=9 (same as the French AF model)

Using model=10, I left mine sitting at the RAMP with the engines idling for 30 minutes and the smoke never cleared. When I changed it to model=9 and left it sitting at the RAMP with the engines idling for 30 minutes, no smoke showed up. I was still using the Japanese textures.

Mark