Mercury 90 hp fuel problem

Smiley1957

Seaman Apprentice
Joined
Jun 13, 2018
Messages
30
new primer bulb and hose. Ball will not get hard. Unplug from motor and hard as a rock. Get motor started and runs like crap. Unplug fuel line and she purrs like a kitten. Any suggestions?
 

Chris1956

Supreme Mariner
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Mar 25, 2004
Messages
28,398
I will assume this is a carb motor? If so, check carbs for flooding. Next check is fuel pump for leaking diaphragm.
 

Smiley1957

Seaman Apprentice
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Jun 13, 2018
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30
Just rebuilt carbs and fuel pump. Carbs r real simple but maybe I screwed up on fuel pump. There was one part left over in the kit that was not in the pump when I took it apart. It was a black disk. Same size as the clear disk. Maybe pump was rebuilt in the past. They may have used the Sierra kit. I used the OEM kit. I will probably have to take it apart and inspect. I did see another thread where a guy was asking about this same black disk. I’ll have to look and see if if I threw that away or not .
 

Smiley1957

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Jun 13, 2018
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30
Took fuel pump off . Took it apart and everything looks fine. Put it back on . Pump ball and not hard. Took a piece of hose to listen for any air leaks while pumping ball. Put hose down throat of each carb. Can hear air woshing as I pump the ball . I would think if it was a float sticking gas would be coming out of one of the carbs. Not happening, just the air sound. From all 3 carbs. Don’t understand.
 

Chris1956

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Mar 25, 2004
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28,398
Is the primer bulb facing the correct direction? Are you sucking air from the fuel tank? Does the fuel line upstream of the tank have an air leak?
 

Smiley1957

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Jun 13, 2018
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30
I checked arrow on bulb and its facing the correct way. It’s brand new 50 Bucks . As far as an air leak none. When I unplug the line from the motor the bulb gets rock hard.
 

Chris1956

Supreme Mariner
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Mar 25, 2004
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28,398
When you unplug the fuel line from the motor, it seals. The primer bulb should get rock hard.

When the fuel line is connected to the motor, the primer bulb should pump whatever is in the fuel line. If you have fuel it should pump fuel. If you have air, it will pump air. Since you hear air in the carbs, I suspect you do not have fuel in the fuel line....
 

Smiley1957

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Jun 13, 2018
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Any suggestions? Is it possible I messed up on carb reassembley. As far as rebuild it was simple. Hardest part was removing and reinstalling. Will have to possibly take carbs off. Don’t really want to but
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,771
You are pumping air. The issue likely in the line, tank or anti siphon valve. Logic says if no fuel is getting to the carb the problem is not in the carbs.
 

Smiley1957

Seaman Apprentice
Joined
Jun 13, 2018
Messages
30
Ok thanks for the help. Couldn’t deal with it any longer. Took it to a friend and let him figure it out. Just want it to run right to put it up for sale.
 
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