See full version: Idle Adjustment 20 hp Mercury 4-Stroke
You can go here to download the complete factory repair manual for virtually any year and model outboard engine. The manual covers every aspect of service and repair—from a simple oil change to replacing a piston or water pump—covers it all. [links]
Can I make small alterations to the idle speed screw to achieve smooth idling? Are there instructions online that can show me step-by-step how to adjust the idle on a 2009 Mercury four-stroke 20hp? I am not even sure where the idle screw is located.
To properly make idle modifications make sure the throttle link rod is adjusted correctly, then start the engine and allow it to run for 2-3 minutes or until fully warm. Attach a simple tachometer to cylinder #1 spark plug lead and measure idle RPM while it’s out-of-gear. With the tach attached to the spark plug lead begin to adjust the idle screw until factory recommended idle RPM is achieved.
Idle speed in neutral is factory set at 950 ± 50 RPM and 900 ± 50 RPM when in gear. This applies for both manual start and electric start 15 and 20 horsepower 2008 thru 2010 models. The idle adjustment screw location is pictured below.
How do I change the idle setting on a 20 hp Mercury 4-stroke? The engine runs too slowly when in neutral and stalls every now and then. The engine also shutters as its ticking over. more
I have included a picture of idle adjustment procedures for your model. These adjustment procedures and specifications may differ depending on the year and model of your Mercury outboard. more
Adjusting your 35-HP Mercury outboard's idle is more than turning the idle speed screw; you also have to adjust the throttle cables and the cam follower. The extended time required for this process means that a flushing attachment may not supply enough water to avoid engine damage. The 30- to 40-HP Mercury outboards all used some version of the Walbro WME carburetor, not all of which have a mixture-adjustment screw.
Move the throttle to the "Idle" position. Move the throttle cable sleeves up or down in the mounting bracket until the cam-follower roller until is centered over the raised mark on the cam, and tighten the cable jam nuts.Tighten the cam-follower screw and turn the idle-speed screw inward until there is a gap of 0.005 inches to 0.04 inches between the cam and the cam follower. here
Turn the motor off and shift it into "Neutral." Use a standard screwdriver to loosen the cam-follower screw on the carburetor. Loosen the idle screw, located to the left of the throttle until the throttle plate is closed: the throttle-shutter positioner will not touch the taper of the idle speed screw. Loosen the jam nuts on the throttle-cable sleeves, just below the throttle cam.
Set the mixture screw (see Fig 1) by first screwing in until the screw stops, bottoms out. DO NOT FORCE OR BIND AS THIS WILL CAUSE DAMAGE TO THE SCREW AND IT�S SEAT IN THE BODY OF CARBURETOR. Back out the screw 2 full turns. more
All settings are done with choke disengaged or warmed up so that the choke is fully opened and disengaged. This is done on automatic choke carburetors by first opening the choke butterfly by hand and inserting a wood block or wedge of some kind to hold open while the linkage is cycled (linkage operated through its full movement ) to clear the choke cam. (You will hear a metallic click as the cam is released. You can check the fast Idle screw under the choke assembly to confirm that it is not in contact with the choke fast idle cam.)
Start set up by confirming carb base line settings. Do not depend on the factory delivered settings. Check them before the carb is installed.
If you should need to call REDLINE for technical assistance we will need to know your final settings to help. Technical assistance is free for the first 60 days of purchase. Units in service over 60 days may be assessed a service fee. All charges will be noted up front after a brief consultation to determine any possible defect. If the carb is out of the warranty period and no defect is determined we will estimate the possible cost of tech support or recommend literature available that may help. [links]
You must return items in their original packaging and in the same condition as when you received them. If you don't follow our item condition policy for returns , you may not receive a full refund. more
Refunds by law: In Australia, consumers have a legal right to obtain a refund from a business if the goods purchased are faulty, not fit for purpose or don't match the seller's description. More information at returns .
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