More than likely it has nothing to do with the bypass at all. There is something going on with the turbine, the pump, the RPM sensor and the ecu. My advice would be to take the turbine out of the jet and put it on a bench and see if you can get it to do the same thing.

I believe you are getting a situation where the ECU thinks the turbine is spinning at the high RPM of full power when it's not. As a result you get too much fuel flow in the turbine for the actual RPM's present and you are flooding the turbine causing the fire. The black soot is kero that isn't burning all the way.

So I would check your RPM sensor. It may be giving a bad reading to the ECU. Also, I have seen stuck starters slow down the turbine while the pump thinks it needs more fuel. Same thing will happen.

The sucking sound is probably kero catching on fire inside the turbine.

Just my guess.

Andy