I'll take pics of the heater hopefully tonight and post em here...sounds simple enough, and what you describe about it running rich also sounds right. Last time I used it was at the end of July, used it to dry out the joint compound in the corners, even with all 3 of my garage door's open the fumes were too bad for me to say in the garage.
This is an older unit, so I just assume buy a rebuild kit from the get go and do it right....
You may get lucky and not have to rebuild anything. The pressure adjustment is most often used to fine tune the burner unit for whatever type or grade of fuel you are using in them. Being there is a fair amount of viscosity and heat content difference between different grades of kerosene and diesel fuels the air adjustment is how you set the burner for the cleanest burn depending on which fuel you are using. Your burner may simply be set to rich for whatever fuel and grade you have in it at the moment.
On the back of most good models there is a small pressure gauge that read between 0 and 15 or so PSI. That is your reference point for setting the air/fuel ratio. If yours has a gauge and it's reading way at the top end the odds are the pressure is set too high or the little regulator valve is partially clogged.
Easy fixes for that and no rebuild is needed. Just take the set screw out and clean the inside where the spring and ball sit with some either and an air hose. A lot of times that spring and related internal parts get gummed up with old fuel residue and it throws the settings off.
I picked up three commercial torpedo heaters a few years ago that had air pump problems.
The local dealer claimed they were brand and model specific and no parts were available so they got the customer to buy all brand new ones.
I knew different so I picked them up as scrap. About 20 minutes online and I had their actual manufacture and equivalent sub models tracked down. After that it was about 10 minutes on eBay to find the aftermarket rebuild kits to repair them. Total cost for me to fix all three was less than $100 to make about $1500 worth of heaters work like new!
I gave one to my brother and one to my dad. We don't use them much but when anyone needs a lot of heat fast they are the got to machines to do it!
So if you do need to rebuild yours the odds are you can find aftermarket parts online rather cheap.