Inconsistent Idle RPM

[DangerMouse1]

I've got a mercruiser 5.7 carbureted engine.

I replaced the carb and am getting a steady idle of 700, good vacuum 20hg, and tested for vacuum leaks, and found none.

My problem is that sometimes when I have throttled up and then come down, I get a lower or higher idle rpm. The only thing I can think of, is that it is the throttle cable coming into the carb, maybe it is sticking or I have to adjusted it correctly?

Anyone have any suggestions, thoughts on why this might be? Any 'quick' fixes?

 

[achris]

Disconnect the throttle cable from the carb. Set the idle speed with the idle speed screw. Them adjust the cable (by moving the brass barrel) so that there is a very little closing pressure on the throttle arm. (I suspect you didn't adjust the cable when you put the new carb on)

Chris...

 

[DangerMouse1]

Disconnect the throttle cable from the carb. Set the idle speed with the idle speed screw. Them adjust the cable (by moving the brass barrel) so that there is a very little closing pressure on the throttle arm. (I suspect you didn't adjust the cable when you put the new carb on)

Chris...

Thanks will try that. I had done it, but probably readjusted and didnt swivel it again. Will see what happens.

 

[Bondo]

Thanks will try that. I had done it, but probably readjusted and didnt swivel it again. Will see what happens.

Ayuh,.... Boats don't have a throttle return spring, so the cable has to push the throttle linkage up against the idle adjustin' screw,....

 

[QBhoy]

How are your manifolds and risers? Any sign of water on the plugs ?