I always use a bypass with all my installations (currently I have three, exactly the same) but I am having a problem that I have never come across before.

Here is what happens; the start goes perfect but when I go to full power after start I end up with fire inside the bypass. When it happens, it sounds like something is getting sucked into the engine, but there is nothing. Afterwards, the engine is perfect, only everything is black and scorched from the residue left after the fire on the inside of the bypass and on the engine. Everytime I have to use my Co2 FireX to put out the fire.

Today I had a perfect start and flight with the specific jet, but the above happened when I wanted to have another flight. Previously the same thing had happened on the same jet - then I changed the bypass because it burned badly, I changed the engine and it's ECU.....but obviously I have not found the problem.

Could it be that some sort of back pressure forms and forces all the trust back into the front of the bypass?

Your thoughts will be appreciate.

Jan