idle mixture screws

[COxs11newbie]

Well, in my endless quest to get my midnight special running correctly I pulled the carbs for a more complete cleaning. Got to the idle mixture screws and two of them are completely stripped at the head. Previous owner must have tried to adjust them and done some serious damage.

So, anyone know the best way to get these out? I'm not sure if an easy out will work since there's not much screw body to lodge in to. Also, is there anywhere to get replacements? I did some searching and all I could find was a post saying yamaha discontinued them.

I swear if I can't get this thing running right soon or keep running in to problems like this, this old bikes gonna turn in to one heck of a firework show!

[Ken Talbot]

See if you can get in there with a fine round diamond burr in a Dremel tool and cut yourself a new slot. Look for something aroud 1mm in diameter. Just be careful not to grind too close to the sides of the bore so you don't damage the threads in the body of the carb. Once you get the scrws out, you can use an abrasive wheel in the Dremel to rework the slot before you put the screw back in.

[COxs11newbie]

Good idea, but both of the screws are in the seated position which has to be about 3/4" down the hole. Do you think I'll be able to get the tool down inside it that far and still be able to cut accurately?

[TopCatGr58]

I remember a suggestion a while back, about getting a reverse cutting drill bit, one that cuts turning CCW instead of CW, and be small enough to drill into the top of the adjusting screw, start drilling it, and use a slow totally variable speed drill, after a short distance into the screw, the bit may bite enough to start turning the screw out under VERY slow speed or even by hand!?

I'm thinking they are still available, possibly from motorcyclecarbs.com, rob reil is very helpful and may be able to provide help in this, he's been the sponsor for the Yamaha Classic bike rallies in NC and Ga. past couple of years, he rides a 850 triple, knows carbs.....it's his business!!!!!
T.C.

[Ken Talbot]

A diamond burr like this one will get in there to do the job:

You are only working in brass so the cutting will be pretty easy. Use a good task light and maybe a set of binocular magnifiers and you should be okay. TopCat's idea of drilling out with a let handed bit would be good it you can find one. Another option would be to use the dremel just to drill enough of a hole to get a regular drill bit into the brass, drill it out some more, and use a small conventional extractor. If you can do it the way I suggest, you will be able to reuse the pilot screw.

[COxs11newbie]

OK, I think I'll try to cut a slot in it first and get it out that way. I'd like to be able to reuse the screws. Even if that doesn't work I suppose I'll be still able to use a screw extractor to get it out. Do I need to worry about metal shavings getting into the carbs after I pull the screws out? Is there anything else I should do to ease getting these out? I've been soaking them in penetrating lube, so hopefully that loosens them up some.

Thanks for the suggestions....

[Czekus21]

You have the carbs pulled to do this job. It's a good idea to pull them apart and give the insides a good cleaning and to make sure everything on the inside is adjusted properly. (ie. floats.) also would be a good idea to pull your jets and make sure that they're good and clean. Don't forget your compressed air.

[COxs11newbie]

Yeah I just gave them a full cleaning, that's when I discovered the stripped screws. The carbs are still off the bike, so it's no big deal to pull them apart again. I'm gonna try this tonight or tomorrow, so I'll let you guys know if I have any luck...

Thanks again....

[Startrekfanatic]

Speaking of those screws...

Thanks to my son in law whom claims to know everything about carberators, he screwed the screws all the way in and backed them off one & a half turns, which (he said) is "Just where they should be set." Now, can anyone tell me how they should really be set? My '82 XJ 1100 won't start without priming the carbs (squish gas fumes into the intakes).

[TopCatGr58]

Hey there STF,

Well, the Xj's are a bit different with their YICS system. They essentially have the same carbs as the 81's. Are you talking about starting anytime, even after it's warmed up, or just when it's cold? You do know about the choke, don't you??

How are you able to swish gas fumes into the intake without having the airbox off? If you are referring to putting the petcocks in PRIME position, that is only for directly allowing fuel to flow into the carbs bowls, but won't actually put it into the inlets!?

You can try turning the 1/2 turn further out and try them, then another 1/2 turn out until they behave like you "think" they should, but am curious about the situation?
T.C. Live long and Prosper!

[Startrekfanatic]

Top Cat said:

Well, the Xj's are a bit different with their YICS system. They essentially have the same carbs as the 81's. Are you talking about starting anytime, even after it's warmed up, or just when it's cold? You do know about the choke, don't you??

How are you able to swish gas fumes into the intake without having the airbox off? If you are referring to putting the petcocks in PRIME position, that is only for directly allowing fuel to flow into the carbs bowls, but won't actually put it into the inlets!?

You can try turning the 1/2 turn further out and try them, then another 1/2 turn out until they behave like you "think" they should, but am curious about the situation?
T.C. Live long and Prosper!
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This is when it is cold after sitting overnight (or longer).

I ripped out the airbox and put those wire screen type air cleaners, so It is real easy to squeeze plastic gas can fumes directly onto the intakes. Plus it gave me a great big storage space where it used to be.

When I use the choke, it will try to fire, but takes so long the battery starts to get weak, with the gas fumes it fires up after two or three tries.

Before my "expert" stepson messed with the set screws I almost never even needed the choke at all.

After it is started, my engine starts with only a slight push of the starter button and runs just fine all day.

BTW, I meant to say, that was my very first post in this forum.
Great place to hang out.
I suppose I should introduce myself in another area.

[newmaac]

COxs1100newbie,
the screws should not have much resistance to turn. They are held in place with a spring, so that they will not vibrate and change the mixture setting without you doing-so intentionally.

The heads were most likely messed-up when the cover caps were drilled-out, to get at those screws. (don't ask how I know that) lol
It woun't take much of a slot cut into the head to get them backed-out.
I would recomend blowing-out those openings, after cutting the slot, but before trying to back the screw out.
Any small brass shavings might catch in the threads and slow the process.
The screws are still around. I recently bought some on e-bay. I have some decent used ones, if you can not find new ones.

good luck

[newmaac]

STF
Since you are pretty sure that your mixture screws have been adjusted incorrectly, you might take a little extra time and make absolutely certain that he did not break any of the tips-off in the carb bodies.
It is VERY easy to break off a tip when "bottoming them out" before turning them backwards.
The key is to use a screw driver that you can get VERY little leverage with, that fits the head well.
I took an old screw driver to the grinder, and made something that fits the slot well, but has a handle that can only be twisted with a thumb and ONE finger.
I don't know about the XJ, but if memory serves, I think that I started at 2-1/2 turns out on the 80 SG.

good luck

[strom]

BTW: Those srews are still avaliable from yamaha... at least I got em bout a year ago... not cheap tho.

LP

[TopCatGr58]

Hey there again STF,

There is a lengthy thread that Mike Hart posted about a year ago when he went to INDY filters on his XJ, and all the fun he had rejetting it to get it to work right, and for the plugs to be right.
Replumbing/rejetting thread on XJ

Sounds like you are quite lean on the fuel settings with those pilot screws turned in so far. Also, with the INDY filters, you may also be a bit lean overall even though the bike may "act" like it is normal, have you checked your plugs lately??

When I did my topend rebuild with 4-1 pipes and Indy filters, I kept the OEM jets, it seemed to run fine with power thru entire band and no hesitations, but the plugs were BLEACH white, way too lean, was concerned about burning up my new pistons! I put in 3 sizes larger mains, and have nice color now and still behaves well, with same mileage!

BTW, welcome to the FORUM. I lived in Angleton for a few months back in the mid 70's before we finally moved up to San Angelo. The thickest fog I had ever driven in there!!! Had to stick my head out the window to see the edge of the road and center line marker!!PHEW.
T.C.