18HP Johnson mixture screw leaking gas

[White Feather]

Over the weekend I discovered my 1967 18 horse Johnson is seeping fuel from around the WOT mixture adjuster when I prime the carb. The motor hasn't been run since last May when the cowling came off and sank in the lake. (That's another story.) I rebuilt the carb just prior to that using a kit purchased from NAPA. No leaks and ran great the couple of times I had it out.

The packing for the mixture screw in the NAPA kit is nothing more then a loose fitting oring that you stuff in the hole before inserting the needle. It did fine for awhile but like I said, it's leaking now.

Is there a better product to use for packing mixture screws, or did I do something wrong? I didn't like the oring approach to begin with but I followed the directions that came with the kit. Something isn't right. Any suggestions would be appreciated.

 

[Chinewalker]

Re: 18HP Johnson mixture screw leaking gas

Hi White Feather,
Might be able to just tighten up the packing nut a bit and see if that takes care of the leak. It should be quite snug, but don't over-tighten it.
The packing in most of the kits I've seen has been a thick fiber washer. An o-ring would probably work, but it is susceptible to drying out, swelling, etc. due to additives in gasoline.
Also, if it only leaks while choking the carb, you might be overchoking it, where excess gas dribbles back out the mouth of the carb. It would dribble straight down, onto the needle valve shaft...
- Scott

 

[White Feather]

Re: 18HP Johnson mixture screw leaking gas

Thanks Scott - I'll look and see if maybe I'm flooding it out and the gas is dripping down like you said. I think I'll also see if I can find some of those fiber washers. Sounds like that would be a better way to go even if it isn't the oring that's leaking. Like you said, orings are subject to drying out and/or swelling over the long run.

 

[Paul Moir]

Re: 18HP Johnson mixture screw leaking gas

You should have a couple packing rings on that one I believe. Your post seems to only indicate one.
Good idea, forget the o-rings. They're far too "grabby" for packing service anyway. I have used regular packing in a pinch, but do get the right stuff. PN 307583. Any dealer worth his salt should have it, it's used on all sorts of J/E carbs.