Problems starting K & B 7.5 inboard

[h20ski]

This is a used motor. I'm at the point where I can start the motor but it does not idle smoothly - it runs rough at idle - almost like surging. Then it leans out and I have to shut the motor off. When the motor leans out the carb is hardly open.

This looks like an old style carb. There is an idle adjustment screw and the high speed needle which is set at 3.5 turns.

Is it time for a new carb as I'm not sure what to do next.

Thanks in advance for any help or suggestion. JIM

 

[Duck899]

This is a used motor. I'm at the point where I can start the motor but it does not idle smoothly - it runs rough at idle - almost like surging. Then it leans out and I have to shut the motor off. When the motor leans out the carb is hardly open.
This looks like an old style carb. There is an idle adjustment screw and the high speed needle which is set at 3.5 turns.

Is it time for a new carb as I'm not sure what to do next.

Thanks in advance for any help or suggestion. JIM

Take a piece of fuel tubing about 12" long and put it on the fuel nipple on the carb and blow through it. Do this as you rotate the barrel of the carb and see what happens as you close the barrel. It should flow air all the way untill it shuts off, even then you should be able to blow through slightly. On the old gray carbs they had a mixture screw that had an o-ring on it and this screw should be flush with the housing. The high speed needle usually runs around 3-1/2 to 4 turns open as you have it.

I suspect the mixture screw is set too lean. Don't concern yourself with getting a nice smooth idle, just blip the throttle to keep it running.....Once its on the water it will run fine....as long as its rich enough....

 

[Foolwitools]

Check the carb mounting o-ring. if the o-ring is bad or is not seated propperly, it will never idle right.

Bob the Fool :blink:

 

[h20ski]

The O ring is something I haven't considered. I'm going to change the hoses today and I'll look at the O ring. Thanks J