Antique gas cookstove (Glenwood Duplex) with an oven problem

[Halll]

My problem is with an 82-year-old Glenwood Duplex, a great old hunk of cast iron, which ran for years on natural gas and has been converted to propane. The top burners are OK. The oven has two speeds: high when it's working to reach temperature and low when it's just maintaining temp. At high, the odor - presumably incomplete combustion - is unbearable.

At low - maintenance - the flame is a good blue throughout; I don't see the yellow tips people talk about with propane. At high, the flame becomes higher (of course) and lazy, and there is a fair amount of what to me is orange - and this is with the air shutter fully open.

There is no plate above the burner - just a solid shelf the full width of the oven interior - so I can't judge flame size in the classic way, but maybe it's too high. There's a serious black deposit on the bottom of that shelf directly above the pilot, so perhaps the pilot assembly needs more cleaning. I've cleaned the burner as best I can.

As a total amateur, all I can think to do is try a smaller orifice. Does that seem reasonable? Or is there another avenue I should be going down?

 

[barmstrong2]

I would start by cleaning everything. Remove the burner, burner orifice, disassemble the pilot and clean all of it. Use a small drill bit, by hand, to clean every port in the burner. Dunno any rust and debris from the burner. Blow the orifice clean. Don't open the orifice with a drill bit. Clean the pilot assembly completely.
Put it all back together and try it, with the oven floor out, so you can see the flame. Sharp, blue flame is what you want on the pilot, as well as the main burner. Orange indicates too rich, too much has/not enough air. Yellow indicates too lean.
The pilot should have a throttle somewhere. A small valve with a slotted screw for adjustment. Tweak it so you have a nice blue flame. The high/low for the main burner is going to be a balance between the two. Adjust the air so you have the best flame on either setting, priority being on high. I would expect to have a lean, yellowish flame on the low setting, with a clean, blue flame on high.

 

[Halll]

I would start by cleaning everything. Remove the burner, burner orifice, disassemble the pilot and clean all of it.... Orange indicates too rich, too much gas/not enough air....

I did clean everything pretty well, I think, although I plan to re-clean the pilot assembly, since I notice a slight propane odor when just the pilot is burning. But here's my basic question at this stage: If I'm getting too much orange even though the shutter is fully open, what does that tell me about the orifice? Is the hole too large? What other symptoms would the wrong size orifice produce?

Thanks very much for the help so far.

 

[barmstrong2]

The orifice is not going to open by itself, so, if the burner was burning correctly, and nobody has molested it, it's the same size it always was. My bet is the ports in the burner are rusted, or dirty. Rust won't wash out. The best way is to find a drill bit that fits tightly through the ports, clean reach port with the big, by hand. Use a pin vise or something.

 

[Halll]

The orifice is not going to open by itself, so, if the burner was burning correctly, and nobody has molested it, it's the same size it always was. My bet is the ports in the burner are rusted, or dirty. Rust won't wash out. The best way is to find a dull bit that fits tightly through the ports, clean reach port with the big, by hand. Use a pin vise or something.

I'm not suggesting that the hole in the orifice just got larger. I'm thinking that the orifice that was installed during the conversion from natural gas to propane may have been improperly sized. The oven has never burned properly - that is, without serious odor - since the conversion. I do like the idea of using a drill bit to clean the ports. But I still wonder if a too-large orifice could be why full air doesn't improve the burn and reduce the odor.

 

[barmstrong2]

I'm not suggesting that the hole in the orifice just got larger. I'm thinking that the orifice that was installed during the conversion from natural gas to propane may have been improperly sized. The oven has never burned properly - that is, without serious odor - since the conversion. I do like the idea of using a drill bit to clean the ports. But I still wonder if a too-large orifice could be why full air doesn't improve the burn and reduce the odor.

Got it. In that case, I would replace the burner orifice with a new one drilled at the appropriate diameter for the btu design of the burner. Being as old as it is, there may not be a data plate. I'd start at 35,000 btu and try it. If the flame appears to be small, I'd go to 50,000 btu. I don't have my orifice sizing chart with me at the moment. It's in the truck. I'll post the diameter for each tomorrow.

 

[Halll]

Got it. In that case, I would replace the burner orifice with a new one drilled at the appropriate diameter for the btu design of the burner. Being as old as it is, there may not be a data plate. I'd start at 35,000 btu and try it. If the flame appears to be small, I'd go to 50,000 btu. I don't have my orifice sizing chart with me at the moment. It's in the truck. I'll post the diameter for each tomorrow.

Actually, the oven burner is rated - so I'm told - at just 15,000 BTU. (We're talking a 1934 model stove, don't forget.) It's a Glenwood burner marked 42D-102, for what that information may mean to you.

I really appreciate your effort and your knowledge.

 

[Halll]

Further thought:
The burner seems to do all right at low speed (after it satisfies the thermostat setting, when it's just maintaining), but when it kicks into higher gear to raise the temperature, the (larger) flame is lazy and smelly. Does it sound as if a larger orifice might solve that problem, or does it sound more like maybe there's a blockage in the vent? Or could it plausibly be either?

 

[barmstrong2]

Lazy and smelly sounds more like a rich flame. Too much gas/not enough air. Or, more likely, just a dirty burner.
The orifice is fixed, so, it's going to give XXX btu, regardless. If the ports in the burner are rusty or dirty, they are, in effect, over gassed. I know you said the air is full open, so, you're left with gas as a variable.
The burner looks like it's simply drilled with holes, but, it is engineered to operate within the btu of the design. That's why I keep going back to the burner. I'll post a pic from the orifice sizing page right now.

 

[barmstrong2]

This chart shows only drill size by number. The drill sets are numbered. Not sure how much that's going to help you. I'll find a dimensional chart later.

 

[Halll]

Lazy and smelly sounds more like a rich flame. Too much gas/not enough air. Or, more likely, just a dirty burner.
The orifice is fixed, so, it's going to give XXX btu, regardless. If the ports in the burner are rusty or dirty, they are, in effect, over gassed. I know you said the air is full open, so, you're left with gas as a variable.
The burner looks like it's simply drilled with holes, but, it is engineered to operate within the btu of the design. That's why I keep going back to the burner. I'll post a pic from the orifice sizing page right now.

That's my thinking too: too much gas. Which is why I'm thinking I should go with a smaller orifice. Less gas would mean the air balance would be better. The chart shows #57 size for 15K btu. I think I have a #56. Thanks again.