reducing orifice size to eliminate sooting

[Brooks89]

I have a Marquis-Bentley 39" propane fueled fireplace, running with a glass media tray, glass ember media and a 4 piece 'driftwood' log set.
The unit was professionally installed, is vented to specs, and my propane supplier has replaced/checked/calibrated the regulator on my gas supply.
The fireplace was shipped from Kingsman already set up for propane and has a #51 orifice for the main burner with the shutter set wide open. I was experiencing some soot build up on one portion of the log set. It's installed/set up as per the manufacturer's specs, and some small repositioning of the log and glass media around it seems to have all but eliminated soot on the log set.

Problem is I am getting soot deposits on the glass and black porcelain lining of the fireplace. It's noticeable after a few hours running time.

I spoke with Kingman's technician and we discussed taking the nozzle size down one size to a #52 orifice. I am waiting on a call back from my installer and asked them to contact with Kingsman with any questions.

This seems a A-T-F issue and since everything else checks outs I don't see a way of leaning out the fuel mixture except to lower the nozzle size.

Just figured I throw all this out here for opinions on whether this hopefully solves my issue, Any thoughts? Anyone done something similar with good results?
We've also continued to have an 'extinguishment pop' issue but that seems to have subsided to a degree based on rejiggering glass media and maybe from the burner itself 'breaking in'? Wondering too if the smaller orifice might help with that too.

 

[DAKSY]

That's more than the orifice, I think. I'd check the venting.
If there is any gap allowing exhaust to re-enter the combustion air,
that will mess up the ATF ratio & the unit will soot like crazy.

 

[Brooks89]

oh boy, that doesn't sound good. How would one be able to check the vent for a gap allowing exhaust in the combustion air?

 

[Fingerlakes Fireplace]

Open the glass just a whisker (on the bottom) and run for a few hours, and see if the sooting improves.

 

[Brooks89]

Update: Dealer Tech swapped replaced the #51 with a #52 orifice supplied by Kingsman at no charge. He also re set the glass media and log set using much less of the glass media overall and with a very spare amount of glass on the burner pan, but filled in the forward part of the burner pan using 'platinum ember' rock wool and some additional ember material resembling strands of silver wire. (anybody have any info on this material? He showed me the package but I didn't get the brand info).

The results are really excellent. Flame level is reasonable, the platinum ember material gives a great effect, the sooting is gone, and the "extinction pop" gone as well. A #51 orifice has a .067" nozzle diameter, a #52 orifice has a .0635" nozzle diameter, in terms of area that's approximately 13% less which seems to be working really well.