1968 18 hp Evinrude Low Idle Screw Problem

I have been having problems with my 1968 Evinrude carb. The boat ran so well most of the summer and than died. While checking the carb I noticed that the nut holding the low idle adjusting screw in had backed out. I went through the carb and put it back on. I adjusted the carb per the detailed instructions on this site. I ran it in a rain barrel and it ran great. It did have a little sputter or cough when idling.
I took the boat out today and first off it didn't want to crank. Guess it didn't like the 40 deg weather. Once it started, it didn't want to idle again. I got it running and took it out to heat up the engine. Once it warmed up it would run but kept coughing or sputtering. Finally it died and I noticed that the Low Idle screw nut had backed out again.

Has anyone had this problem or know a fix. I love this little boat, but this motor is killing my back. When I bought it in the spring it would bush my john boat 28mph and started on the first pull.......ugh Help

The fix is to actually get a kit for the carburetor. All you did was disassemble and reassemble.
If you get an OEM kit you will notice there are small fiber washers and at least one small nylon washer. These are "packings" for that nut.
The reason you are having that issue is that the packings both seal out the air and they put resistance on the idle mixture screw so it will hold a reliable
idle mixture. Without them the mixture screw will be able to move freely.
The OEM kit is the only full kit out there. Comes with everything needed to properly rebuild a carburetor once cleaned. Aftermarket kits are not complete.

I have gotten non-oem kits that include the packing washers, for what that's worth. :?:

Anyway, if the shaft that holds the needle (usually referenced as "nut" in the drawings) is the culprit then throw something on the threads and tighten it down. I would use pipe tape just cause that's what I got. Use something that will provide friction, but will be "breakable" when time to disassemble.

Several of the aftermarket kits do not include such basics as the float assembly. Replacing the old fuel logged cork float with the new style is always a good way to go in my book.
I will only recommend proper shop service techniques. I do not encourage shade-tree repairs. If needed to get you home, fine. But not when there is a proper way to do it and you have the time to do it right.
As it is you already have to do the job a second time.

You want to invent your own packing....go right ahead.... If that is your route then you are on your own.

Easiest thing would be to go here: https://www.marineengine.com/parts/johnson-evinrude-parts.php?year=1968&hp=18.

Pick your model and goto the carb group. You'll notice they list a kit for rebuild. In this kit you can see that packing washers are included (packing washers are part of a basic kit). It should be noted that a float is not included in the basic kit. This is due to the float not being replaced at every carb re-build.
Once you get the kit number you can shop around for price.

If however, your issue is not the packing washers, but indeed the nut being somewhat loose (this happens with things as they age). Then you need to either replace the nut or the carb body (whichever is out of spec). However, you can also put something on the nut, gland that will allow it to remain in place and sealed.



Then again, if you have not done a rebuild in some time it would be good to do that and then seat the nut.
Carb kits can be bought that have the float as part of the kit or do not have the float. Sometimes you just have to get the float as an aside (if needed).

Pappy is right though. The carb should be properly rebuilt.
If the needle/nut has new packing washers it should work fine. Typically the only issue you'll run into with new stuff is the needle will be somewhat difficult to turn (which is good 'cause it has a good fit with the washers and thus a good seal - and the nut should not back out).