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Duo-Therm model 76003-5. It's an old one. Directions says to swap the regulator caps and to orifice the burner and pilot. However I cannot figure out how to do that. I found tid-bit of info. elsewhere that said the orifice is after the gas valve, and just before the burner. But this is inside the furnace and innacessible. Suggestions?

You probably have to remove the gas valve to get at it. You should be able to take it apart and remove the orifice. Take some pictures of it so we can see exactly and maybe be able to figure it out. Make sure you have the gas supply shut off to the unit while working it.

Is this a Gas Burner setup? Hard to tell on my phone right now.

That is a gas burner. The only time you change orifices is when you change fuel types, natural to LP or vice versa, unless it was set up wrong in the first place. Why are you wanting to change the orifices? As for their location, the pilot orifice is located under the nut that is threaded into the pilot assembly at the main burner, visable center right in first picture. The main burner orifice is that big slit nut looking thing with the hole in it in the second picture. It may not come apart and if you get it off I doubt one will be available. Duo-Therm has been out of business a long time.

DaleM, yes we are changing because of different fuel types. It's a "mobile" home that has been moved to another location, using LP gas. I did learn that Duo-Therm is no longer unfortunately at the beginning of my search. Thankyou for your insight into where the orifices are located however. There wasn't any real info. on the net for DuoTherm. As an update, we've opted for a replacement furnace. And I think we will happy with that decision. I'll be installing it myself so I may have more questions soon It's made by Coleman, and is an electric unit.