carb woes

[graybird78]

not sure how to start this thread. but have been experiencing carb problems since last fall. all started with carb flooding over. took carbs off and found 1 float sticking.fixed that and started having backfire on decel. found out that turning out mixture screws helped . so now it is fall, so parked bike for the winter.now with weather getting nice decided to look at carbs again. got carbs off and disassembled. what a mess.so much crap in carbs. 1 float needle was wrong for this application.2 out of 4 floats hanging up bad on pins.2 floats not even usable. had another set of carbs to use for parts. took floats and needles out of spare carbs.both sets of carbs are off of 80s. completely cleaned carbs with cleaner and lots of air. used new floats in carbs and couldn't get float height right .found out floats were not even from side to side.after much adjusting i think i finally got them right . went by book specs of.906 or 23mm. are these right .bike is stock. did notice tho that my original set of carbs had 110 mains all the way across.the other set had 110 and 120 mains.whats up with that. should i use the latter of the 2 sets as this is what clymers says should be in carbs. bike never really ran smooth. i'm mechanically inclined.so any advice. just really want to get bike running its best.i don't exspect a new bike ,just one that runs good. any help would be great.thanks to all.

[chevy45412001]

jets

I'm not a mechanic nor do i claim too be 1,they told me at the bike shop i visit the reason for that was the middle two cylinders dont recieve the same amount of air ,as the outside carbs.I have an xj and run the same jets all across,seems to run just fine.Just my 2 paso's.

[rneal55555]

I think they have so that the two cyl that run hotter get a riched mixture to help them run cooler. Pretty sure there's a thread on here that talks about it. It's the inside cylinders that should have the larger jets if I remember right. But I could be wrong. (I won't go it which part of my anatomy my memory is shorter than) Resn is supposed to be that in 1980 epa made them build them to run leaner for air quality. And running lean causes them to run hotter.

[bkr]

Carb Main Jets

Hey Greybird Have 115 M J in outside carbs 117.5 in center ,came with 115M J . Center plugs run a better colour ( tan) ,better idle. Bike is an 84 XJ. My parts bike is an 80 SG with 110 M J. Worked ok when together. bkr

[nashville_bill]

My '81 has 110s in all four carbs and runs fine. I tried to richen it up with bigger mains but it was too rich. I think most of the carb problems you read about here are float or intermediate/low speed problems.

[TopCatGr58]

Hey there Greybird78,

I can't find my reply to another Xsive about his 81carbs, but the 80-81's are the same. And your's is a special as well. Have you thrown away your Octopus yet?? My 81 also had stock 110's across all 4! Unless you've altered your breathing, ie. Indy filters, and/or 4-1 pipes or better 4-2 pipes/headers, then you probably won't need to go up any in size of the main jets, and you can just run them all 110 across!

The other thing I wanted to mention is the idle circuit. The 80-81 carbs had brass caps over the idle/pilot jet screws on the top of the carbs at the neck where they attach to the intakes! If they are still there, then your idle/pilot circuit is probably still quite gummed up. You'll need to drill them gently and not very far down, they are about 1/8" thick and the screw heads are not far below that. I used a sheet metal screw to put into the caps after drilling a modest hole, then locking pliers to clamp on the screw, then tapped against the pliers to pop them out! Then you can have access to the pilot screws, remove them, careful, lots of little rubber/metal washers and spring there, and the tips are delicate.

Then clean out the carbs again thru that circuit, then put the screws back in, "gently" seat them, then back out 1 & 1/4 turns. Then fresh plugs, and run for a while and check color. If too white, you can back out the screws to richen. See tech tips for rejetting guide if you have modified your intake/exhaust! Also check for Bread Stick tie bench synch! HTH.

[Ken Talbot]

Just for reference - when you do a bread tie sync, you can expect your bike to idle at something like 3500 to 4000 rpms the first time you start it. The technique works okay for getting all four butterflies to about the same setting, but they will then be way too far open for a correct idle speed. Be prepared to bring the idle back down with the idle adjustment screw. And, unless you are way better than I am with the bread tie method, you will still need to do a proper vacuum sync to get things right on.
BTDT

[graybird78]

re-carbs

hello topcat ken and others. my bike is completely stock cept for foam air filter.no exhaust mods or any other mods. i like my bike stock.just seems to me that these carbs are very tempermental.my original carbs have 110 mains in all 4.I did remove the caps covering the idle circuit.when i disasembled the carbs i took out all the jets and idle screws even the emulsion tubes to clean everything out. i think i was pretty thorough in cleaning.got some gunk out. blew lots of air in all the passages i could find.blew air one way then back the other way. seem to have good air flow from what i could tell. my floats were messed up and one needle vavle was not correct.the brass insert in float pin hole were broken.my spare set of carbs had the mains as described in clymers manuel.so not sure which is correct for my bike?. I set the floats at book specs. but have read on here that may be incorrect? .906 or 23mm?haven't had a chance yet to run bike after work.no time.will get to it this week. my biggest problem with carb cleaning and adjustments was the floats were not balanced from side to side. measure one side and the other side was either to high or to low. a little patience on my part and i think i got them to read the same from side to side. sorry for such long posts but this is nerve racking to get it right .never had this kind of problems with my kz. I know bad word here . thanks again for the help and words of encouragement.

[nashville_bill]

You can check the real float adjustment by attaching clear 1/4" tubing to the bottom of the float bowl and opening the drain screw. The Yamaha workshop manual ('81 supplement page 12-4) stated correct adjustment puts the gas 1/8" below the place where the float bowls meet the attaching screws. The Clymer manual describes the procedure on page 256 and says that the gas should be 1/8" below the top of the float bowl. I don't know which is the correct adjustment but think that the important thing is that they are all the same.

Good Luck!

[graybird78]

carbs

Yee-haw it runs .and not to bad.did have slight flooding at first but well placed hit on offending carb solved that. as far as checking floats with clear tubing, what do i screw in place of bowl cap. did have to adjust idle speed.i'm glad it runs somewhat decent. now at least i have a starting point.left 110 mains in all 4 jugs. no black smoke or backfiring.

[bkr]

carb woes

Hey Greybird The XJ has a outlet on the bottom of the float bowl to use a clear plastic hose to check fuel level. The XS needs a special fitting to get a reading. I am not sure if this will be accurate or not , worth a try. bkr

[randy]

A good rule of thumb to follow with this is:

If you have a brass plug at the bottom of the fuel bowl, take the carbs off to set the float hieght, there is no established method of checking these with a sight tube setup.

If you have a phillps head screw at the base of the bowl with a nipple right next to it, that is your sight tube connection. Attach a clear hose to the nipple, curve it upwards and loosen the screw until fuel flows out. The fuel will stop at the hieght of the floats.

Hope this helps.

Randy

[graybird78]

my carbs have the brass plug in bottom of float bowls.

[randy]

Then you have a '78 or '79. Or, at least that is the year(s) of your carbs.

Randy