Joel the hydrohot just like the aquahot requires enough air flow through the unit to get complete combustion .
There are several things that could cause your rich operation
1) burner nozzle ( dirt or poor atomization,improper spray pattern)
2) low voltage condition causing slower blower speeds and not enough air movement
3) blower bearings dragging again causing lower blower speeds
4) exhaust pipe particle blockage ( rust and soot buildup causing poor air flow through combustion chamber)
5) air leaks around the burner head at the combustion chamber ( grommets on the electrical and fuel passthroughs )
6) melted down combustion chamber air swirler causing poor air flow and incomplete burn
I would start with a good service
1) remove the burner head
2) inspect the combustion chamber tube for cracks and the swirler for signs of aluminum melting down
3) clean the combustion chamber with a wire brush to remove soot buildup
4) using a fish tape pull a small rope through the exhaust pipe from the combustion chamber to the tail pipe tie a rage to it and pull it back a d forth to clean and verify the exhaust is clear
5) remove the rear black plastic cover from the burner head and spin the motor by hand listen for bearing noise in the blower housing
6) if you have an optical tachometer power up the motor with 12 volts and measure the shaft speed at the coupler this should be done with the fuel pump drawing fuel for the proper load the spec is 4500 RPM +/- 300 however every one I've tested has been in the 5000 RPM range.
7) if you have a fuel pressure gauge to screw into the nozzle opening check fuel pressure as described in the manual the spec is 145 PSI and is adjustable on the side of the pump
replace the rear cover
9) replace the burner nozzle with a new 0.35 gph 60* nozzle
10) reinstall the burner tube the seam in the tube must face up 12 o'clock position
11) reinstall the burner head
12) cycle the burner and check for any air escaping around the burner ( grommets and combustion chamber) no leakage is acceptable
Finally to answer your question yes there is an air adjustment aperture on the air intake this is there officially to allow CO adjustment but as you move to higher elevation it needs to be opened up to make up for the thinker air density.
Remember if the unit has been flooded ( too much fuel ) there will be a buildup in the exhaust which will take several cycles to clear before the unit will run clean therefore I don't recommend making any air adjustments until the unit has been serviced and run for a period of time to clear itself before making the air adjustment.
There is a screw on the aperture usually at the right side of the intake tube loosen the screw and move the screw in the slotted whole towards the combustion chamber will increase the air flow ( leaner)and pulling it back towards you will decrease the air flow ( richer)
Before moving it take a paint pen and index the screw for future reference.
Hope this helps
Eric
