Think someone posted this else where and was confirmed that it was a bug - that it shouldn't do the big jump as you say when engines are stable. NGX had same issue - and was fixed in SP, so looks like the code maybe have carried over with the BUG still in it.

 

Nice video - I had a kettle once that sounded like that

So...not sure if anyone's had a look at the inside of a combustion chamber, but, there's fire in there.

 

This isn't some little fire in your back yard that gets larger over time.  The fire appears pretty suddenly.

 

Thus, there's a jump in temp.

 

Skip the first 15 seconds:

 

well, looks like this el al 777 200er doesnt have that fire, at 0:34, you will see how the egt increases

 

 

after that pmdg 777 sturtup looked unrealistic to me.