View Single Post
Old 10-04-2009, 07:45 AM
Wildkat's Avatar
Wildkat Wildkat is offline
XS Special Gurette
Join Date: Apr 2004
Location: Location, Location
Posts: 3,406
.... moving on....

Turn the carbs around, put a thick cloth under them so the posts don't break or get damaged, and unscrew the screws holding the tops of the carbs/ diaphragm covers and remove them, the diaphragm springs and the brackets between the carbs.

Slide the diaphragm assembly and needle out. These can be delicate, so handle them with care; the rubber can tear easily, and dropping them on a hard surface can damage the slides enough to make them unusable. After you get them out, hold them up to a strong light and look for holes. Minor pinholes, you may be able to repair them. Big holes or rips, you'll need new ones. This used to be major disaster if you needed to replace these, there's now a reasonably-priced replacement available... look here: Upon reassembly, make certain to match up this 'tab' on the diaphram with the matching relief in the carb body. Check the jet needles sticking out of the slides; look for bends and heavy wear or 'roughness'. If they're bent, you may be able to straighten them, but badly worn ones should be replaced. Make sure they move freely in their holes; if not, they'll need to be removed and cleaned.

Here's a pic of the '78-79 type jet needles. They assemble in the order shown into the slides, and are held in by the c-clip on the far right. Note that these are adjustable by moving the c-clip on the needle; the '80-82 ones aren't and only have one position. The 'standard' position of the c-clip for the '78-79 is in the middle. The '80-82 are similar, but are removed by taking out the two screws inside the slide as seen in the pic above.

Turn the carb around again and look in the hole where the main jet came out. You'll see the 'needle jet' also known as the emulsion tube. If it pushes out easily into the slide area, remove it. If not, soak it with penetrating oil and tap it out gently from the bottom of the carb, i.e. the main jet hole, with a thin flat screwdriver (round the sides of the hole so you don't damage the thread for the main jet) or a small wooden dowel or pencil. Don't try to pull it out from the slide hole with pliers, you run too much of a risk of damaging the tube. I usually use a small wooden dowel or a pencil to gently tap it through...

The emulsion tube out...

If you look at the inlet/airbox side of the carb body you'll see at 8 o'clock the air pilot jet to be removed and cleaned. Again, make sure the screwdriver fits firmly in the slot. The small jet at the 4 o'clock position isn't removable. The other hole(s) are vents, the large oval one being for the diaphram/slide, the other one or two for the bowl.

On top of the outlet side of the carb (small mouth which connects to the carb boot/engine) is the idle mixture screw which is the screw you turn to adjust your idle mixture, e.g. when you Colortune. Pictured is the late carb, so this screw is down inside the tower. You may find this hole plugged if the carb hasn't been rebuilt, you need to remove the plug. Drill a small hole in the plug (don't go too deep or you'll damage the screw), then install a small screw in the hole and pull the plug out. After exposing the idle screw, this is the same as all the other jets; the slot is easily stripped, so make sure your screwdriver is sharp and you keep pressure on it while you turn. Some penetrating oil can help. Once you get the screw out, you should find (in order) the screw, a spring, a small washer, and a small o-ring. You'll probably have to pick the washer and/or o-ring out with a paperclip. The o-ring will likely have to be replaced. These parts will come in a rebuild kit, so don't worry about their condition unless you don't plan to buy a kit.

The early carbs are slightly different; the screw is exposed, simply remove it. If the plastic 'anti-tamper' cap is still present, cut that off. All you have is the screw and the spring, no other parts. But these screws are noted for the tips breaking off in the carb body if they're turned in too far, so check for that. The tips can also be damaged, so look for that too. Again, these will be furnished in a rebuild kit. If you have broken tips stuck in the carb bodies, do a forum search for the various methods of removing them. Sometimes they need to be drilled out...

Optional: You can turn each of your idle screws in until they're lightly seated, keeping track of and recording how many turns so when you reinstall you can 'reset' them as they were. This may or may not be helpful, and if you suspect broken tips or they turn very hard, you may want to pass.

Check your choke linkage for operation; if it's frozen or very stiff, you'll probably have to break the rack apart...

... so you can remove the enrichener pistons ('starter plunger') as shown here. Remove these with a socket. These should move freely (except for the slight spring tension) out and snap back in. When disassembling the choke linkage, watch for a small spring and ball in this hole in the number 1 and 4 carbs if you're working with XS carbs; this 'detents' your choke, so try not to lose them. The XJ carbs won't have these holes or the springs/balls. Frozen or stiff linkage is why you find carbs with the choke lever broke off....

If the springs and/or balls get lost or are already missing, you can replace the balls with a common 1/8" diameter ball-bearing. The springs can be ordered new from Yamaha (over $9 each!) but I offer lower-priced alternative replacements. PM me for details... crazy steve
One last thing. There's seals on the throttle shafts, and these do leak on occasion. If you suspect yours are bad, this will require removing the shafts, a rather difficult job. We're not going to cover this here, look in the forum for more specific information. The seals are rather expensive also and won't be included in a rebuild kit.

Ok, the carbs are apart, on to cleaning and reassembly....