22 NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
Figure 33
Main Burner Factory Air Shutter
Opening Setting - Inches (millimeter)
Model Natural
Gas
Propane
Gas
MPB-3328 Fully Closed 3/16"
(4.76 mm)
MPB-3530 Fully Closed 3/16"
(4.76 mm)
MPB-4035 Fully Closed 3/16"
(4.76 mm)
MPB-4540 Fully Closed 3/16"
(4.76 mm)
Note - The air shutter for the burner primary
air opening is factory-set. Do not adjust the
factory-set position. The factory-set position is
shown in Figure 33.
Air Shutter Adjustment Guidelines:
Amount of
Primary Air
Flame
Color
Air Shutter
Adjustment
If air shutter is
closed too far Flame will
be orange Air shutter
gap should be
increased
If air shutter is
open too far Flame will
be blue Air shutter
gap should be
decreased
Step 11. BURNER ADJUSTMENTS
Flame Appearance and Sooting
Proper flame appearance is a flame which is
blue at the base and becomes yellowish-orange
in the body of the flame.
When the appliance is first lit, the entire flame
may be blue and will gradually turn yellowish-
orange during the first 15 minutes of operation.
After 15 minutes of operation, if the flame is
blue, or if the flame is orange with evidence of
sooting (black tip), the air shutter opening may
need to be adjusted.
If the air shutter opening is closed too far,
sooting may develop. Sooting is indicated
by black puffs developing at the tips of very
long orange flames. Sooting results in black
deposits forming on the logs, appliance inside
surfaces and on exterior surfaces adjacent to
the vent termination.
Sooting is caused by incomplete combustion
in the flames and lack of combustion air enter-
ing the air shutter opening. To achieve a warm
yellowish-orange flame with an orange body
that does not soot, the shutter opening must be
adjusted between these two extremes.
Air Shutter Adjustment Guidelines
• Ifthereissmokeorsootpresent,rstcheck
the log set positioning to ensure that the
flames are not impinging on any of the logs.
If the log set is properly positioned and a
sooting condition still exists, then the air
shutter opening should be increased.
• Themoreoffsetsintheventsystem,thelarger
the air shutter opening will need to be.
• Anapplianceoperatedwiththeairshutter
opened too far, may have flames that appear
blue and transparent. These weak, blue and
transparent flames are termed anemic.
• Propanemodelsmayexhibitameswhich
candle or appear stringy. If this is present
and persists, adjust the air shutter to a more
closed position, then operate the appliance
for a few more minutes to ensure that the
flame normalizes and the flames do not
appear sooty.
The following chart is provided to aid you in
achieving the correct air shutter adjustment
for your installation.
WARNINGS
• Air shutter adjustment should
only be performed by a quali-
fied professional service tech-
nician.
• Ensure front glass panel are
in place and sealed during
adjustment.
CAUTIONS
• Soot will be produced if the
air shutter is closed too much.
Any damage due to carboning
resulting from improperly
setting the air shutter is not
covered under the warranty.
• The air shutter door and nearby
appliance surfaces are hot.
Exercise caution to avoid
injury while adjusting flame
appearance.
Burner Air Shutter Adjustment
Setscrew - Factory located in the natural gas
position; relocate set screw for LP/propane
gas in the alternate position. See table for air
shutter openings for these setscrew locations.
Air Shutter
Venturi
Ref. Air shutter Patent:
U.S. Pat. 5,553,603