Mercruiser 3.0 carb issues

[brian3127]

Carb is off a 1978 engine.
1985 boat so I don’t know what year the carb is.
Engine Serial number
4920382
First video
Is there supposed to be this much slop between the linkages
Second video.
turn the volume up to hear the clicking coming from the butterfly valves at the bottom of the carb.
The reason I ask is when trolling the rpm’s change all the time without moving the throttle.

 

[brian3127]

Carb is off a 1978 engine.
1985 boat so I don’t know what year the carb is.
Engine Serial number
4920382
First video
Is there supposed to be this much slop between the linkages
Second video.
turn the volume up to hear the clicking coming from the butterfly valves at the bottom of the carb.
The reason I ask is when trolling the rpm’s change all the time without moving the throttle.

 

[Scott06]

Clicking seems like accelerator pump arm inside float bowl is rubbing. Take bowl top off i think you will see the arm that attaches to the accelerator pump pivot shaft is installed incorrectly. I think if it get flipped around during a rebuild it rubs

the linkages seem ok, except accelerator pump one may be related to whats making the clicking. Pump should be under pressure from spring in it and would take up that slack.

someone was in there during a rebuild and reassembled it wrong

 

[achris]

When posting about a carb, it's useful to include the Make and Model number of the carb itself (as well as the engine serial number, which you did, thanks). It's usually on a red tag held on by one of the cover screws, or on the body of the carb.

The 140s in '78 could have either a Rochester 2bbl or a MerCarb 2bbl.
The Rochester has 2 idle mixture screws (one for each barrel), and the MerCarb a single mixture screw.

like this for the Rochie....


Or like this for the MerCarb...

Once we know exactly which carb you have, our answers can be more accurate.

If it's a MerCarb it should be a 1389-8490, if it's a Rochester it should be a 17043184.

Chris.........

 

[Scott Danforth]

The reason I ask is when trolling the rpm’s change all the time without moving the throttle.

I would lean to the mix not being right and the carb has debris in it.

 

[brian3127]

When posting about a carb, it's useful to include the Make and Model number of the carb itself (as well as the engine serial number, which you did, thanks). It's usually on a red tag held on by one of the cover screws, or on the body of the carb.

The 140s in '78 could have either a Rochester 2bbl or a MerCarb 2bbl.
The Rochester has 2 idle mixture screws (one for each barrel), and the MerCarb a single mixture screw.

like this for the Rochie....
View attachment 357251

Or like this for the MerCarb...
View attachment 357252
Once we know exactly which carb you have, our answers can be more accurate.

If it's a MerCarb it should be a 1389-8490, if it's a Rochester it should be a 17043184.

Chris.........

it is a Mercarb it has one mixture screw. I will look for the serial number on the carb when I get home today.

 

[brian3127]

Serial number on the carb

 

[brian3127]

Clicking seems like accelerator pump arm inside float bowl is rubbing. Take bowl top off i think you will see the arm that attaches to the accelerator pump pivot shaft is installed incorrectly. I think if it get flipped around during a rebuild it rubs

the linkages seem ok, except accelerator pump one may be related to whats making the clicking. Pump should be under pressure from spring in it and would take up that slack.

someone was in there during a rebuild and reassembled it wrong

I put my fingers on the butterfly valves. While moving the throttle and they are moving before the click sounds. So you are probably right about the accelerator pump.