Proheat M125 - Manual (Page 30)

An increase in the compressor air pressure over the nozzle will add more
atomized fuel into the combustion tube; however the combustion air provided
by the combustion air blower remains constant resulting in a rich air/fuel
mixture and possibly black smoke from the exhaust.
A restriction in the amount of air through the combustion chamber (restricted
air intake, dirty heat exchanger plugged exhaust) will also result in a rich air/fuel
mixture as the compressor air pressure (and atomized fuel flow) remains constant.
A restriction in the fuel line, filter, screens, or nozzle fuel passage will reduce
the atomized fuel/air flow into the combustion tube: however the combustion
air provided by the combustion air blower remains constant resulting in a lean
air/fuel mixture and possibly gray/white smoke from the exhaust.
A decrease in the compressor air pressure over the nozzle will reduce the
amount of atomized fuel/air into the combustion tube; however the combustion
air provided by the combustion air blower remains constant resulting in a lean
air/fuel mixture and possibly gray/white smoke from the exhaust.
Examples:
Figure 2-2. M80 Fuel Delivery Theory of Operation.
BLOWN AIR
BLOWN AIR
BLOWN AIR
BLOWN AIR
BLOWN AIR
BLOWN AIR
BLOWN AIR
BLOWN AIR
BLOWER
MOTOR
COMBUSTION
AIR BLOWER
AIR
COMPRESSOR
FUEL
SOLENOID
(N.C.)
FUEL
PUMP
ATMOSPHERIC
PRESSURE
NOZZLE
FUEL 0 PRESSURE
VENTURI EFFECT
AIR
ATOMIZED
FUEL
FRESH
AIR IN
FRESH
AIR IN
FUEL
DRAWN
IN
FUEL TANK
AIR
FILTER
FUEL
FILTER
AIR PRESSURE
2.9 psi
M
FUEL
REG.
5 – 10 psi
REGULATOR
SCREEN FUEL DELIVERY
BLOCK SCREEN
2-5 PROHEAT M-SERIES G-II PCM SERVICE MANUAL