RMH with a lid on the burn area...and FLAMES!

Hi, all. I have my rmh up and running, but i have a question...i have a keg can around my brick burn chamber, it is insulated with perlite...
i am experiencing burn-back when i have its lid on..there is a two inch hole in the lid. is this because the lid allows the burn area to become too hot?
just wondering?
thanks!

Eric : YES ! By now you have solved your problem yourself, however you should be aware that if the top was placed on (with the 'bung hole' covered)
you could smother the fire which due to the extreme high temps will still pyrolyze the wood so you would have a condition where you have a soldering fire
and super heated flammable gases ! Remove the cover and - - -Have you ever seen the move '' Backdraft !''? ??

You should do 1 of two things remove that barrel, or remove the insulation from around the Feed Tube ! When this re-posts I'm sure that you will
get a similar 2nd opinion ! be safe , keep warm, PYRO -Magicly yours , - Allen L.