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  Strange idling characteristic of Mercury 125HP

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Author Topic:   Strange idling characteristic of Mercury 125HP
Wet Foot posted 08-22-2003 01:39 PM ET (US)   Profile for Wet Foot   Send Email to Wet Foot  
My 2001 125HP Mercury makes a missing sound when fast idling in neutral for a cold start. When I slow it down to slow idle after it warms, the noise is gone. Even once warm, any raising of rpm in neutral causes the backfiring/missing noise. The dealer says this is a normal characteristic of the 125HP 2/4 cylinder engine. Does anyone else experience this or is my dealer mistaken?
Jamie 20 outrage posted 08-22-2003 06:16 PM ET (US)     Profile for Jamie 20 outrage  Send Email to Jamie 20 outrage     
A good mechanic will hold this boat overnight so he can experience a cold start and adjust the idle/mixture screw to the rich side to get rid of what we often call sneezing. If the carbs cann't be adjusted, I would remove them and soak them in carb acid to clean the areas that are hard to clean. Then adjust them. Sneezing is never acceptable when heard regularly.
Lil Whaler Lover posted 08-23-2003 07:02 AM ET (US)     Profile for Lil Whaler Lover  Send Email to Lil Whaler Lover     
Wet Foot, what is the rpm when you say fast idle? At 1,800 rpm the motor switches from running on 2 cylinders to 4 cylinders. Do not set your fast idle at 1,800 as the motor may literally become confused as to whether it is running on 2 or 4 cylinders. Try it at 1,500 or 2,000 and see if it smooths out.
If the noise continues and it is like a "popping" sound then it is too lean and the idle jets should be set richer.
Wet Foot posted 08-25-2003 01:28 PM ET (US)     Profile for Wet Foot  Send Email to Wet Foot     
Thanks for the input! I'm not sure about the rpm's, but will check it when out again. All I know is if I advance the throttle more than straight up neutral, the popping occurs.

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