Mixture Screw Question

[Ganboy70]

New owner, 84 stock...so sync my carbs last night. I set all of my mixture screws as well and noticed that # 1 screw feels loose and doesn't have the notch feel of the others.  Plugs look fine but #1 does look a bit sooty compared to all the others.  My question is, is there an o-ring possibly missing from # 1 screw?  PO definitely was messing with these carbs so wondering if there may be lots more to find!

[andyb]

Unscrew the mixture screw fully, and pull it out.  You're going to find (hopefully!) a few things under it.

(And for the life of me I can't find a decent picture today or I'd show you:)

-The mix screw itself
-A spring that the screw goes through
-A tiny washer that acts as a seat so the spring doesn't chew up the soft body of the carb
-A tiny oring that acts as a gasket

The oring needs to be not all chewed up to seal well.  The screw itself needs to have a nice even taper to it with no big wear spots and not bent at the tip.  If you screw it fully in until it seats, you should be able to feel the tip poking through into the outlet of the carb (between the throttle blade and the head).  With the carbs on, it may be possible to see it poking through if you hold WOT, lift the slide up, have a flashlight, and a mirror, but it'd be tricky.

If this doesn't fix things for you, there's a couple things to look at that can cause one plug to get ickier than the others.  In order of things to check, least work to most work:

-You sure it's soot, not oil?  Leaking valve stem seals or rings can get things ugly on a single cylinder.  Soot will be dry, powdery (almost like super fine, super black dust).  Sometimes you'll see one exhaust pipe discolored more/less than the rest from the different mixture burning at a different temperature (if your pipes are shiny, can't see it otherwise).
-Check to see that the choke plunger is moving like all the rest of them are.  There's an oring in that assembly that can leak too, but that takes more surgery to see.
-Pull the airbox/filters off and see if that slide isn't moving freely, I've seen them stick in an up position.. just give them a push up and they should all drop at about the same rate.
-Pull (all) of the tops off the carbs and take the needles out, is that one different?  
-Pull the carbs off (sorry!) and check float height.  You can check fuel height on the bike, but the drain screws in the bowls often freeze solid, so don't fight them too hard, you'll end up with more problems than you started.
-With the carbs off and the float heights matched to the right spec, there's still a possibility of leaking oring(s) at the float needle seat.  To replace those, the float pin (the thing it hinges on) has to come out, the float and needle has to come out (check the condition of the needle tip when you're there, incidentally), and the brass seat also has to come out (it's a slight press fit, but can be a bastard to get out)... then replace the orings on the seats.
-If the carbs are off, you can look into the orings on the choke portion as well.
-With the carbs off you can also check to ensure the pilot jets are all the same, and someone didn't drill one out or something.
-You can also check to see if perhaps the emulsion tubes (needle jets) have one being out of round from wear--you may have seen earlier that the #1 needle had wear on it worse than the others, or was bent a bit.

A mix screw being set too far out can cause black plugs.  

If you get to the point of pulling the carbs off, you're money and time ahead to simply replace all the rubber in them and give them a good cleaning.  

[Ganboy70]

Andy, thank you so much...going back out to the garage to do more inspection.  Keep you posted.

[Ganboy70]

So fast-forward ahead here (I already have it apart)    Doesn't look there is anything really holding the screw in there except an o-ring/washer perhaps but I may be wrong - there may be nothing except the screw in there.  Plug looks fine, no oil deposits, just carbon fouling from probably the obvious.  Is it possible to replace these parts needed without removing the carbs?  Hopefully?

[andyb]

If you can get the mixture screws out, you're apart far enough to replace everything associated with them.  Problem is, there's a chance that it's been screwed up for awhile, rattling around, etc, which means there's likely filings of brass/aluminum in there, and that tiny hole at the bottom leads directly into your motor.  Inspect it really carefully to make sure that the hole is still all in good shape (i use a camera, good lighting, and a macro setting to take detailed pictures that I can zoom in on the computer and inspect super closely), and if you're happy that it's in decent shape, putting the new bits in is quite easy.

[Ganboy70]

I just hope to God that the PO may have just forgot to put everything back together properly after the "so-called" carb cleaning that was performed.  She's in good hands now...  Thanks again Andy, time to get things back right...

Cheers