750-204
Profire D/LND
4-9
4.7 — Cam Trim Adjustment
with the lever, the slower the rod moves. The angles of the driven levers on the jackshaft can be adjusted to vary
the rate of change. The closer the rod to the hub of the lever, the less distance it will travel. Increasing the lever
length on the damper, metering unit and valve(s) decreases flow rate.
4.7 — Cam Trim Adjustment
After low and high fire adjustments are complete, final adjustment is made with the cam assembly to obtain a
good air/fuel ratio throughout the entire firing range. The input of combustion air is fixed at any given point in the
modulating cycle. The fuel input may be varied to obtain correct flue gas readings. The adjustment is made to the
metering cam by means of the 14 adjusting screws which are turned in (clockwise from the hex-socket end) to
increase the flow of fuel, and out (counterclockwise from the hex-socket end) to decrease it. a 3/32” hex key is
required. It will be necessary to cut off the short end of a hex key to approximately 3/8” to adjust the first two
socket head setscrews at the low fire position. Take a combustion analysis at various points of the cam profile.
Adjustment can be made without cycling the burner then, then operate the automatic modulating cycle to assure
satisfactory results. Tighten the locking setscrews.
FIGURE 4-5. Cam Trim Adjustment
4.8 — Firing Rate Controls
Firing rate adjustments are made at the modulating motor linkages to the combustion air inlet damper, air-oil
metering pump, and main gas butterfly valve. Settings are determined by the operating length of the levers and
the angular position on the shafts. Increasing the lever lengths on damper, pump, or valve decreases the flow
NOTE: It is essential that the cam spring, cam follower bearing wheel, and cam follower arm at the pivot point be
greased sparingly every month to ensure smooth operation of the cam assembly. Regular automotive bearing grease
should be used.
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