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Mercury 25 excessive vibration

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bigfoot_jack

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I have a 2003 Mercury Bigfoot

I have a 2003 Mercury Bigfoot 25 hp outboard that vibrates at idle speed even when in neutral. The vibration is only reduced slightly at higher rpms. This is on a pontoon boat and the whole thing shakes. We call it the "massage boat". I changed the spark plugs but observed no improvement. Could the flywheel be out of balance?
 
"No, but the carb idle mixture

"No, but the carb idle mixture sure needs adjustment.

Jeff

PS: If the flywheel was out of balance, the motor would shake WORSE at higher rpms!"
 
Thanks Jeff
Do you know where

Thanks Jeff
Do you know where I can find a picture or diagram that will show me where the mixture adjustment is done?

Jack
 
put a timing light on each plu

put a timing light on each plug wire to make sure they all fire. shouldn't idle that bad
 
"The adjustment is a slotted s

"The adjustment is a slotted screw in the top front of the carb. You need to warm the motor fully, tie the boat to the dock so it won't move, and put the motor in gear. Idle it down as low as it will go without stalling, then SLOWLY turn the adjustment about a 1/4 turn at a time. Doesn't matter which way you start turning it. If the motor idles worse, go the other way. When it's sounding better, be sure to wait 15 seconds between each adjustment to let it settle in.

When you're happy with the idle, add an 1/8 of a turn counter clockwise to your adjustment.

Tricky for someone whose never done it before, but doable. Oh, and be prepared to have to restart it a bunch of times before you get the adjustment close.

Jeff"
 
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