Johnson J8REEM Idle adjustment

Hi my son has a 1999Johnson 8hp which has a knob at the end of the handle for adjusting the idle. It also has an idle screw at the top front of the carburetor. I can't figure out how to properly adjust the idle, is it a combination of both. When I loosen the screw on the carburetor by approx 1 turn it appears to be very loose and doesn't seem to make any difference to the running of the engine. Any advice would be much appreciated.

The adjustment on the end of the tiller handle is simply a mechanical rpm adjustment... increases or decreases the mechanical stop range setting.

The adjustable idle screw at the top front portion of the carburetor adjusts the fuel flow in comparison to the air flow (a mixture adjustment)... see the following.

(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.

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.

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Hi joereeves thanks for reply. Looking at the schematic diagram for the carbureter can see an idle adjustment screw (part 30) and fuel mixture spring (part 29). I think I might have this incorrectly adjusted, any idea of how many turns to tighten. I can't see how this affects the fuel mixture as it seems to sit on a lug and doesn't appear to affect the air flow to the carbureter.

You are running on a few misconceptions.
Number 17 on the drawing is a plain old plug. It is tightened for a seal, and is not an adjustment.
Numbers 29 and 30 are your idle stop screw assembly. The screw is adjusted to provide proper idle speed AFTER the idle timing is verified to be in spec.
Don't know what the spec is, but it will be somewhere around TDC.

Look on the stbd side of the top plastic plate, and notice number 15. That is your idle mixture screw. Under that plastic plate are three tiny holes. One is larger, but there are two very tiny holes that must be clear. All your idle fuel flows thru those holes.

Thanks, I checked these holes are clear, when you say to lightly seat the s/s needle valve in is this to touch or begin to compress the spring. I can start the engine but then can't start it again when warm. I am going to ask a mechanic to check the compression.