Idle problem

[snookguy]

I have a 1990 70 hp Johnson.

It will start up no problem and run at higher rpms, but when I take it to idle it shuts right off.

The fuel filter is new, the gas is new, the plugs are new. I'm pretty sure it has something to do with the adjustment of the carb because as it runs it starts to spit and sputter and smoke as if it is running rich.

The problem is that I have no idea what to adjust or where to start. I fairly mechanical, but I'm just not sure what i'm looking for.

Any help would be a great. I have spent five years building this boat and I am down to this to fix before it hits the water.

Thank you

 

[woodducker]

Re: Idle problem

Try cleaning the carbs, soak them over night, use compressed air to make make all is clear. the smallest trash can cause problems. Get yourself a good repair manual that the best thing lots off info in there. it will give you adjustment settings for your carb. goodluck.

 

[tashasdaddy]

Re: Idle problem

1st it could just be idleing to slow. each carb also has a slow speed mix adjustment screw. they each have to be adjusted independently. top starboard side on carb, screw with spring on it.

(Carburetor Adjustment - Single S/S Adjustable Needle Valve)
(J. Reeves)

Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.

Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.

Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

Note: As a final double check setting of the slow speed valve(s), if the engine has more than one carburetor, do not attempt to gradually adjust all of the valves/carburetors at the same time. Do one at a time until you hit the above response (die out or spit back), then go on to the next valve/carburetor. It may be necessary to back out "all" of the slow speed adjustable needle valves 1/8 turn before doing this final adjustment due to the fact that one of the valves might be initially set ever so slightly lean.

When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.