MerCruiser 120 1968 2.5 not idling tight

[RMELAN]

Hey All, I have this 1968 I’m restoring and got and issue with a rough idle and when I give it a little it stalls. I’ve changed the plugs, coil condenser, points and rebuilt the carb. After I rebuilt the carb it ran great then a couple weeks ago it started having this issue. It did not have a fuel filter so I installed a spin filter and took off the top of the carb to look for crud it looked clean. I tried to adjust it don’t thing it made a difference. Any help would be appreciated!

 

[RMELAN]

It’s not idling right, rough and when I give give it some gas and it quits.

 

[Scott Danforth]

first, start with the basics. is the motor healthy? what are the compression numbers? a good motor should be 140psi or so, a tired motor will be about 110psi per cylinder

second, what is your fuel pressure (you will need the test adapter) it should be between 4 and 6 psi

third, what is the fuel quality like? is there water or debris in the fuel?

4th, you may need to go back to the carb.

 

[Scott06]

In addition to Scott’s comments Check fir vacuum leaks not only at carb base but if I recall the intake on these older had a split casting top with a gasket on it . May be loose or need new gaskets if not done.

the fact that it ran well after carb rebuild makes me think maybe a bolt loosened up and your sucking air. Symptoms sound similar to a 65 Pontiac I had that I changed everything ... except the intake gaskets last.

 

[RMELAN]

I just pulled out the mechanical fuel peel pump, looks brown and gritty the diagrams look good. I would you recommend I clean the fuel pump? Thanks!

 

[Scott06]

I just pulled out the mechanical fuel peel pump, looks brown and gritty the diagrams look good. I would you recommend I clean the fuel pump? Thanks!

Not sure what you meant as auto correct took over. But yes if there is debris in the fuel system to have to clean it out. You may have a situation where debris was in your tank clogged the carb. You rebuilt the carb which is now plugged as the fuel system keeps feeding debris into it. On a boat of this age likely you will have to empty out the fuel clean it all out replace lines as needed until you can get clean fuel to the carb consistently.

 

[RMELAN]

Thanks, I cleaned the fuel tank first thing when I got the boat. The boat did not have a fuel filter so a few weeks ago I put a fuel water separator on it. I pulled the fuel pump out an cleaned it and now it’s running good again. Hope it stay running good! Thanks for the tips!

 

[Scott06]

Thanks, I cleaned the fuel tank first thing when I got the boat. The boat did not have a fuel filter so a few weeks ago I put a fuel water separator on it. I pulled the fuel pump out an cleaned it and now it’s running good again. Hope it stay running good! Thanks for the tips!

possible if there was grit in there that it was not pumping properly And starving the carb for fuel.

 

[ronc35869]

Not sure what you meant as auto correct took over. But yes if there is debris in the fuel system to have to clean it out. You may have a situation where debris was in your tank clogged the carb. You rebuilt the carb which is now plugged as the fuel system keeps feeding debris into it. On a boat of this age likely you will have to empty out the fuel clean it all out replace lines as needed until you can get clean fuel to the carb consistently.

Do you still have the motor ?

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