Also have had a C-B FWL-6T that was doing the "flaming pumpkins" out the stack due to bad injectors and/or timing. Seems unburned fuel was getting through the cylinders into the exhaust manifold where it burned when it got enough oxygen. I would guess the FDL's also might have the same issue.

I've also heard of engineers who figured out on the old GE's how to manipulate the throttle to get flames out the stack.

I still think EMD roots-blown engines hold the record for carbon and slobber issues for stack and lineside fires. I do have a GE maintenance instruction on using a steam cleaner for cleaning ports.