Echo PB-620 Operator's Manual page 21

Adjustment Screws
Idle Speed (A) Control throttle opening at idle.
Low (LO) Speed (B) Controls amount of fuel at low speed and
supplementary fuel for smooth progression from
idle to high speed.
High (HI) Speed (C) Controls amount of fuel at full throttle
Before Adjustment
Check that:
• Air filter is clean and properly installed.
• Spark arrestor screen and muffler are free of carbon.
• Blower pipes are installed.
Initial Adjustment
1. With engine off, turn HI speed screw (C) counterclockwise to
stop.
2. Turn LO speed screw (B) midway between stops.
3. Turn idle screw (A) until tip of screw just touches throttle plate;
then turn three (3) turns clockwise.
Final Adjustment
IMPORTANT
Limiter caps prevent exceeding C.A.R.B. and E.P.A. emission limits
and over-rich adjustment, but not over lean adjustment, which can
cause engine failure: Do not exceed recommended HI speed engine
R.P.M. during operation, or for long periods during adjustment.
1. Start engine, run at idle for one minute.
2. Complete warm-up by running at full throttle for 5 minutes,
operating choke twice to clear air from carburetor chambers.
3. Run at idle and accelerate to check for smooth transition from
idle to high speed; if engine hesitates, turn LO speed screw (B)
counterclockwise 1/8th of a turn at a time until acceleration is
smooth.
4. Use a tachometer to adjust idle speed to specifications found on
page 24.
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PERATOR S ANUAL
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