The Autotune controls one solenoid. Like standard carbs, the low pressure flowing over the main nozzle shifts the fuel draw to the high side. The AT learns to control this transition through the Throttle Position Sensor. Knowing when the pressure changes passages in the range to alter the fuel flow at the solenoid.
Bog at idle can also be caused by a rich condition. To test for this, let the saw idle for three to five minutes. If it loads and blows smoke/unburnt fuel, its rich. Possibly the needle isn't seating proper or the pop off was adjusted to much. The condition this fixes is a lean one. From the factory some of these carbs throttle butterfly is sealed to tight, not letting enough air past. In turn, the AT leans the mixture to attain the proper idle speed. If one is to let more air by, more fuel is necessary to maintain the same idle. The 550/545 Walbro carb has a bypass adjustment screw.
550/545
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In
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Out
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