Here's something else to do.
Please realize that this help I am offering is coming from about 2500 miles away, and by just looking at your photos, makes it very difficult.

Try raising the back end of the engine exhaust nozzle about 3/16". Your "up the pipe photo" makes it look like the nozzle is pointing slightly down. Is that from parallax also, or am I going blind?
With the lens centered in the pipe, the engine should look centered...it doesn't. The nozzle looks like it is pointing down.

Just checking one more time might be just what you need to solve the problem.

"Measure twice, cut once".

Harley Condra
BVM REP
JetCat REP