Mercury 9.9 problem . . . - SailNet Community
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post #1 of 6 Old 04-25-2019 Thread Starter
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Mercury 9.9 problem . . .

Sitting here in Manjack Cay. A Canadian fellow with a Mercury 9.9 is having trouble. Engine starts and idles just fine. If he turns the throttle up it runs fine a high rpms for a little bit then starts to die. If he backs off to idle it will idle fine but if he keeps it at high revs it eventually dies.

Says he has cleaned carb, changed plugs etc.

My thought are . . .

his high jet perhaps still isn't clear

He has an air leak in a hose before the carb

Any other thoughts?


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post #2 of 6 Old 04-25-2019 Thread Starter
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Re: Mercury 9.9 problem . . .

Found the issue. Air leak on hose just before fuel pump.

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post #3 of 6 Old 04-25-2019
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Re: Mercury 9.9 problem . . .

plugged main jet
water in fuel
plugged fuel line
fuel line sucking air
plugged fuel/water separator if so equipped
plugged fuel filter
put some "Sea Foam" in the fuel tank and run it as long as possible at idle and off idle if it will gradually increase in speed
float set too low
does it run smoothly at idle? one bad spark plug
other ign problems
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post #4 of 6 Old 05-11-2019
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Re: Mercury 9.9 problem . . .

Just a note on what I found after experiencing the same problem. In the fuel line connector (clip-on onto the motor), there is a stainless ball that is displaced when connected. The ball sits against a small o-ring in the connector to stop leaks when not connected. A crack in the o-ring caused my motor to draw air with enough fuel for idling an slow running but not enough to run at any significant speed.

Dug out the o-ring, popped in a new one, problem solved. Sounds easy, took me a few hour of fiddling with carbs, etc. before I found this.
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post #5 of 6 Old 05-12-2019
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Had a merc 9.9. Was the worse outboard I ever had. Carb troubles over and over again. Too many plastic parts. Wire from choke knob to engine kept coming off. Stupid controls all in handle. Lousy torque. Would labor with just me/bride and groceries. Could only take 4 if no chop. Cover cracked from heat. Never struck any thing. Seal between cover and engine fell off.
Gave it to a cruiser to be used in Haiti. Replaced with 2 stroke tohatsu. Simple engine. No bells nor whistles. Works every time.

s/v Hippocampus
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post #6 of 6 Old 05-12-2019
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That merc mayve been pretohatsu
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