The first step in tuning an oil burner is to understand that the manufactures listed settings are the starting point, not the finish line. The air band and retention head settings they list are fantastic for laboratory conditions using known quality oil, but they usually need some tweaking to work in the real world. These settings will normally get the burner to ignite and run reasonably well; well enough for you to dial it to your application.
The burner manufacturer gives you a bunch of adjustments that can be fine tuned to make the burner run correctly in just about every application: retention head setting, oil pressure, bulk air band, air shutter, and electrode gap. These adjustments are there so you can use them, so...use them!
Now, before you start tweaking anything, you need to be sure the burner can run correctly. What I mean is, don't start messing with the retention head setting, or the electrode gap, or anything else until you check the basics. First, be sure the retention head and the burner end cone are clean, and I mean spotless. Shine a light down the burner tube and take a look, if there is any crud at all on the end cone, CLEAN IT!
Make sure the nozzle pattern and spray angle are correct for the application; this is one area that you shouldn't reinvent the wheel on; stick with the manufacturers specifications. In fact, while you're at it, try a new nozzle; a partially clogged nozzle will never burn right no matter what you do.
Now set the electrode dimensions to the manufacturers spec's; eyeballing it is NOT good enough! If the electrodes are in the oil spray they will carbon up and if they are too far away the oil won't ignite.
Next, check the pump pressure; if the pressure is too low the oil will not atomize, if it's too high the burner will be over fired. Start with the nozzle size and pump pressure that is recommended for the machine. Now set the air bands to the manufactures spec's, this will allow the burner to ignite and run reasonably well.
This is the starting point for tuning a burner, now you have to dial it in to your application. Remember, there are more adjustments to on an oil burner that just the air band. The key to tuning an oil burner is making small adjustments, one at a time, while monitoring the results of the adjustment. If the fire is smokey, don't crank the air band open, make fine adjustments to it, then check your combustion readings. For example; If you open the air shutter to reduce the smoke and the smoke stays the same, but the Co2 drops from 11 to 8, there is likely another problem.
We'll dive deeper into tuning oil burners soon. For now remember the manufactures spec's are a starting point, not necessarily the finish line.