i'm no expert,but i think your smoke stack is to tall,the taller the stack,the more draft it will pull.if it was mine,i would pull the stack off and just run with the bung open and see what it did..how much lit charcoal are you putting in your basket to get it started?
More draft it will pull... mmm I didn't know that. I have the stack welded in the lid soI cut the stack to 6 inches long instead of 36"
I use 1/4 chimney full of cowboy lump. I did fill the barrel up with water and found very small water leaks where the bolts hold my basket and a few tiny pin size holes where the 1/2 inch nippels enter the drum. I had some high temp silicone and put a bead of silicone on the outside of the drum where the nippels and bolts enter.