Strange Carburation Issues... need ideas

[81xsproject]

I am working on a members carbs who had thrown in the towel and asked me for my assistance. So, heres the carbs as they stand:

-ultrasonic cleaned
-passages blown through with spray cleaner and compressed air
-jets soaked in chem dip and blown out
-floats set to 23mm (80's bike and carbs)
-carb kit jets and float valves
-good idle screws
-bench synched

Here's the weird part, the bike is running very rich throughout the rpm range. It is so rich, it is bottoming out the range of my O2 sensor at 10.0:1 AFR and it doesn't even start to come up until around 6k. WOT at around 7 will start to normalize into the 12's. Because of this overall richness, after revving or riding, the rpm's hang to the point that while on a test ride, I was having to brake to force the rpm down. It is worse than riding with the choke on. The carbs are getting an excess of fuel from somewhere...?

Things I know it is NOT;

-Throttle cable adjustment
-SYNCHRONIZATION
-Idle screws or postition
-Float height

My current untested theories are

1. Choke/Enricher plungers not sealing
2. Kit jets are garbage and not properly sized

The only other info I can give is that the kits were pilot and main jets, float valves, and bowl gaskets. Air jets, needle jets, and jet needles are all stock.
Any help is welcome.
ThanXS

[bikerphil]

the kits were pilot and main jets

Genuine Mikuni jets? Off brand jets have given me rich mixture problems before.

[DGXSER]

Alot more knowledgable people here, but I will ask the "If I were a dumb rookie" questions, cause I r one.

What size main and pilots were in the kits? My 81 takes 110 mains all the way across and 42.5 pilots. I know the earlier carbs with the covered pilots take larger jets, so if a rookie was used to working on earlier carbs, might put the larger jets in by mistake? Leave it rich all the way across the RPM range?

Not sure if this would effect or not, but if you pulled the needles at all and put them back in, did you leave the screws on the cover plate loose until you got the needle lined up with the emulsion tube? If not, is the slide staying open from a misaligned needle? DAHIK I am assuming (yes I knwo how that breaks down) that the 80 carbs use the same non adjusting needles as the 81 that have a small disk held down with two small screws over the needles.

Like I said, the dumb rookie questions you probably already looked into or know.

[Ken Talbot]

The carbs can be getting excess fuel from the floats allowing too much fuel depth in the bowls. Take the floats up to 25mm, which will reduce the depth in the bowls by 2mm. This will significantly change the amount of fuel drawn up into the venturi.

When I was working on Tsunami's carbs years ago, that 2mm change gave me an immediate increase of 10 mpg. Trey it, you'll like it!

[petejw]

hey 81,
Like Ken said, try raising the floats,
i was running 24mm float heights with the airbox,
and the needle set 1 lean from the middle,
each mm i raised the floats i would get an xtra 10km out of a tank of fuel.
have u run the bike without the airbox?

[red bandit]

Some 80 carbs have the crossover hole between the main jet tower and the pilot jet tower. If yours does do you have a rubber plug in the pilot jet tower? Just a thought.
I have had a few carbs of variuos years that after a thourough cleaning as you have done would idle and run fine until WOT at upper rpm then they would nose over. They did this with stock/drilled air box or pods. With no air cleaner would run great. Never did figure it out. All carbs parts were stock. I tried diff. float height. I even swaped all parts from a good running carb, it didn't change anything. I don't have an O2 sensor.

[TADracer]

Get a factory baseline

If you truly have 80 or 81 carbs then the pilot jet hole should be open to the bowl and the main jet should be smaller than the 78/79 carbs. But it sounds like you might have some mixed and matched parts in there. I would verify that everything is back to the stock settings and go from there. Here is what I would do.

1. Put in Mikuni 42.5 pilot jets.
2. Put in Mikuni main jets. If carbs are from an 1100G or H use 115 on the 1&4 cylinders and 120 on the 2&3. If carbs are from an 1100LG or LH use 110's on the 1 & 3 Carbs. Or you could probably start with 110 or 112.5 across the board.
3. Check that the main air jet is a 140 and the pilot air jet is a 185.
4. Check the needles for the correct ones. G&H should have 51Z7 needles and LG&LH should have 5GL16 needles. Probably one is a quicker taper than the other and will affect your midrange.
5. Set float level to 23mm - 25mm. 23 is stock but going up to 25 should still be OK. Measure from carb body gasket surface (without gasket) or you can do the level tube thing if you have 81 carbs.
6. Check around for anything else that is out of order then reinstall the carbs.
7. Do a tuneup which is check/gap spark plugs, check ignition timing, set carb idle mixture screws, sync carbs then adjust idle speed, in that order. You must syncronize the carbs any time you make an adjustment or remove them from the bike.

At least you will know you are at the factory starting point which is always a good baseline to tune from.

[81xsproject]

Thanks for all the tips, but I am looking for something a little more out of the ordinary. I have been rebuilding and tuning carbs for these bikes for quite a while as a way turn some extra cash to fund other projects for my bike. So, I am no stranger to these carbs or their stock specs. I have had probably a dozen sets of 80's carbs tuned on my bike and not once has the stock float height been too rich, especially with my bike running pods and a 4-1. I've had stubborn sets that ran lean because something was still plugged up and had to take them back for a second ultrasonic bath/compressed air treatement. But, there is no normal reason for carbs set up to stock specs to run anywhere near this rich without something very weird happening. I like all the ideas, keep'em coming

[psycoreefer]

Have you verified that the diaphragm springs are the right size and length? Did you clean out the vacuum passage in the slide that causes it to rise? If the holes are plugged or the springs are to stiff it could cause a to rich condition.

[boyat68]

You said that you benched synched them, and that you know that it is not a synch problem. I know that I had to run synch my 80s several times before I finally dialed them in as they were running too rich and fouling the plugs. I had to replace the plugs three or more times as the plugs would load up and misfire before I finally synched them in where all plugs were firing and coloring correctly. I do not know if the problem only exist with 80 carbs stock, but that was what it took to get mine working corectly.

[Ivan]

You got good spark in the cylinder? Not with the plug out side the cylinder, or a screwdriver shoved in teh plug cap, but in the cylinder.

It sounds to me like you have the carbs nailed down, and its time to look elsewhere. Weak coils or gunked up plugs delivering a weak spark can cause incomplete burning and all kinds of trouble. The hanging RPM may be from having the idle set high to get it running and when the cylinders warm up, its too much.

Also look for an air restriction.

Sorry if these are elementary, but it is usually the stupid little things we miss. My theory is that we become vast in our knowledge, our brain fills up and we forget the simple stuff. For some reason HOOCH seems to help access the latent memories.

[Larrym]

Quality Control

Ken,

I'd look again at the jet kit. Sure, it was packaged and sold as the "right" part/size. But I've worked in maunufacturing and there's a SOP for "quality control" where the inspector pulls out 5 parts out of 100 made and inspects them. If these 5 pass inspection then the whole lot is "certified" as good and then shipped. If any customer gets a bad part out of the lot then the "return policy" applies. For the record when I worked for IBM, ALL of the parts were inspected/tested before they made it out the door.

I say you've got a "new" part that is not good. Have you tried swapping out the "new" jets with known good (ran well in another carb/bike) jets? And just the sake of history, once you have it running right with the proven performers, you can swap the new ones back and see if it runs like it did in the beginning.

Also, if the slide needles are "stock" then it wouldn't hurt the process to swap them for another "stock" pair and then see what happens.

Nothing makes a woodpile more interesting than smelling a skunk somewhere inside it.

Good Hunting!!

[devilschld]

ty all for giving him the input. they are my carbs after becoming fustrated with the problem i sent them to him.

[thewiz]

any chance that ...

someone else could have shimmed the slide needles up with a washer? OR swapped in pre-80 diaphrams/slides and set them on the wrong clip?. Don't really know if -II slides will even fit into -III's actually .... but just brain stormin' ....

Is it a uniform richness on all cylinders?

[renegade_xs11g]

[QUOTE=81xsproject;189710]I am working on a members carbs who had thrown in the towel and asked me for my assistance. So, heres the carbs as they stand:

-ultrasonic cleaned
-passages blown through with spray cleaner and compressed air
-jets soaked in chem dip and blown out
-floats set to 23mm (80's bike and carbs)
-carb kit jets and float valves
-good idle screws
-bench synched


Things I know it is NOT;

-Throttle cable adjustment
-SYNCHRONIZATION




You say they are bench synched, but you know its not synchronization

I remember some of your posts, I take you for a very good mechanic, but think you've dismissed the most likely cause,

I too, used to think a benchsync was good enuf, but it's really not,
I've had the same set of carb's off of the same bike, so many times I can't count, and benched them every time, I've had the same symptoms you are probably 3 times

just my two cents, I hope I shot wide enough not to wound any feelings, but close enuf to get your attention,