Wow! What an odor!

This is about a very old (80 years) cast iron stove - a Glenwood Duplex - that was overhauled and converted from natural gas to propane, with new orifices. The cooktop burners work OK (so I think the regulator is properly installed and the new orifices are the proper size) but the oven is trouble. It gets to temperature OK, but it emits a powerful odor, which the top burners do not. The odor seems strongest when the oven is working on high. (There are two operational levels: high when it's bringing itself to temperature and low when it's maintaining temperature.) I've done the best I can at cleaning out the oven burner (with a vacuum cleaner), as I did with the top burners, but the oven odor persists. I've tried adjusting the air shutter in both directions but that seems not to help. Does this indicate incomplete combustion, possibly because the orifice may be the wrong size? Should I try a different orifice? With the hole larger or smaller? Could it be that the burner still has deposits of some sort inside? In which case, is there a way to clear them? Anything else I should consider?