Problem with new ribbon burner | Tools Equipment | Forum

I've just recently finished my new forge build- replacing my smaller, open-fronted unit with one that has a front sliding door, baffles and after chamber, and vented to the outside for shop heat control.  I did my research and I'm happy with the design and insulation.

Problem is that I made a new ribbon burner for it-very similar to my last one.  My last one was 4x9", has an internal baffle with holes to even the air pressure out and I ran it on a variable speed blower with an 0.060" propane nozzle, 2" IP pipe as feed.  Fine-tuned the air flow with a notched-in homemade gate valve before it mixed with the propane.  Burner dropped in from the top and had about 20 (? I don't remember exactly) 5/16" holes in the castable as nozzles. 

The new one is 4 1/2 x 4 1/2"  and has 9 holes, (8 in a circular pattern and one in the middle), mounted on the side but has the holes canted down at a 22 degree angle. Same blower, but using a commercial brass gate valve to make it more precise. 0.060 gas nozzle, regulated by both propane pressure and a ball valve. 

Here's the problem with it- it burns really odd.  I light it and if it's low air flow (air valve mostly closed), with plenty of gas, it runs rich and sooty- bright yellow, slow flame.  If I turn up the air flow, it goes immediately from rich to really lean and the flame won't be within an inch or two of the burner.  If I further adjust it, it will burn blue about 2 inches from the burner but then yellow and slow 6 inches away.  If I close the door partially, it leaps out the open portion of the door, but does not appear to burn in the forge hardly at all.  If I close the door completely, it isn't burning in the forge, but rather at the back exit in the after chamber and before it goes up the flue (yes, there are vents in the after chamber). If I open the door at that point, a lovely blue fireball comes out the front after it's open about 5 seconds (again, yes, my face was in the way and I lost most of my eyebrows.  Thank God I was wearing glasses but this only points out the fact I should have been wearing safety equipment like a full-face shield).

What-the-actual-fart is going on?  I've never seen this behavior before in a burner.  I checked the burner and it has airflow coming out all of the holes, and it feels somewhat balanced.  I don't seem to be getting back-burning in the plenum of the burner, and I can't see how mounting it on the side of the unit rather than the top should make any difference how it burns- gas doesn't need gravity to flow.  Even if it had a couple of nozzles blocked, it shouldn't run both lean and rich on the same nozzle, which is what it looks like.

For further data, I have a turbulent generator in the air pipe about a couple inches before the gas nozzle, then 12 inches of pipe to an elbow and then into the plenum of the ribbon burner.

Any thoughts from anyone?  Did I miss some data, or a key, important feature?

Thanks,

Wolff