SeaFoam for older Mercruiser 120 4cyl--worthwhile or worthless?

[redgoat]

My I/O is over 40 years old but still runs well except for some occasional rough idle especially when attempting to dock. Could my engine need a carbon cleaning to make it run better. New plugs, plug wires, points, condenser, timing, carb rebuilt and everything is up to specs. SeaFoam has been suggested by some but I need some feedback from boaters who have actually used it or from those who think it's nothing but snake oil.

 

[dubs283]

Re: SeaFoam for older Mercruiser 120 4cyl--worthwhile or worthless?

seafoam isn't gonna hurt anything but its benefits are probably in your head

the best de-carbon product is to run your engine hard for a bit, and keep doing it every now and then

how many hours are on it??

 

[achris]

Re: SeaFoam for older Mercruiser 120 4cyl--worthwhile or worthless?

My I/O is over 40 years old but still runs well except for some occasional rough idle especially when attempting to dock. Could my engine need a carbon cleaning to make it run better. New plugs, plug wires, points, condenser, timing, carb rebuilt and everything is up to specs. SeaFoam has been suggested by some but I need some feedback from boaters who have actually used it or from those who think it's nothing but snake oil.

Here's an old race/rally driver trick worth knowing....

To de-carbonize piston crowns...
Run the engine until it's good and warm. Remove the air cleaner (flame arrestor in our case). Open the throttle to about 2000rpm. Start pouring DISTILLED water very slowly down the carb throat. Run about a pint of water through. If the engine speed drops too far, slow the water, or open the throttle as little more. I disconnect the cable and operate the throttle by hand as I'm pouring... Works a treat.. It very effectively steam cleans the piston crowns, combustion chamber in the cylinder head and the first part of the exhaust port....

Chris...........

 

[Silvertip]

Re: SeaFoam for older Mercruiser 120 4cyl--worthwhile or worthless?

Chances are carbon is not the culprit. You said you rebuilt the carb. Did you adjust the idle mixture properly after the carb was reinstalled. Did you rebuild the carb or did a shop do it? If you did the rebuild did you fully disassemble the carb, soak it, ensure every passage and jet were squeaky clean and then reassemble with a new kit? Float level and float drop adjusted correctly? Idle speed set correctly? Any vacuum leaks? Leaky intake/exhaust valve perhaps?

 

[Bondo]

Re: SeaFoam for older Mercruiser 120 4cyl--worthwhile or worthless?

Here's an old race/rally driver trick worth knowing....

To de-carbonize piston crowns...
Run the engine until it's good and warm. Remove the air cleaner (flame arrestor in our case). Open the throttle to about 2000rpm. Start pouring DISTILLED water very slowly down the carb throat. Run about a pint of water through. If the engine speed drops too far, slow the water, or open the throttle as little more. I disconnect the cable and operate the throttle by hand as I'm pouring... Works a treat.. It very effectively steam cleans the piston crowns, combustion chamber in the cylinder head and the first part of the exhaust port....

Chris...........

Ayuh,.... I think that's written in the ole British Leland factory manuals for the ole Land Rovers I've had,...
Learned it back when I had a '67 Mini....

If I gotta tear down a Runnin' motor, 'n go deep,...
I still do that trick before I start rippin', 'n tearin'...
Makes for less clean up, before reassembly...

 

[jerryjerry05]

Re: SeaFoam for older Mercruiser 120 4cyl--worthwhile or worthless?

Low speed performance??
Carb? Water in the fuel?
Low idle?
Shift assist not set up right?
New shift cable?
Seafoam in a 4stroke,I don't think it's necessary.
Pull the plugs,how they burning?
Adjust the air.