xs650-C carb ?

tms325i

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I know carb ?'s are asked quite a bit however, i am stumped....

I have done everything in the carb guide (read at least 5-10 times). The problem is the bike will only run on choke and it runs to 4500 rpm once it is warm. When you turn the choke off it sputters and will eventually choke itself out.

Here is my quick list of what has been done:

The carb has been completely cleaned, all jets, ports, needles both in choke system, main, etc. All stock jets, etc. in great condition.

Floats are working, correct height, nice seals.

Diaphragm are complete slides go up and down smoothly. Verified the speed by closing off the top portion (go down nice and slow).

I just changed the butterfly throttle seals (all 4).

I have a 78 carb that works great and runs perfectly on the bike with the same carb holders, no leaks, good seal. I disasembled both of them at the same time and did exactly the same process on both.

There are no air leaks on the intake side. Sprayed everything with carb cleaner,etc.
Also, verified with the 78 carb running perfectly (carb holder verified).


Any help would be appreciated.... I need to send this off to someone as I have spent way too much time with "0" results.
 
Did you rebuild anything other than the butterfly seals? Maybe used the same jets/needles on the non-working carbs as you did on the working carbs? They're different.
 
Everything is stock. The 78 carb has 140 mains (originally jetted for an exhaust and filters) and the 76 (problem carb) has the stock 122.5 main jets. The jet, needle and pilot are all stock.
 
Yes, I matched them all. They are all stock and in good shape and clean. The goofy thing its not like its just a little issue sometimes. It runs up to 4500 and stays there. With the choke off it pops and dies.
 
Okay. Hm. I'm going to assume that your carbs are fairly close to balanced, and that you've actually visually ensured that the butterflies are totally closed. Because if they're off balance, that would explain that behaviour totally.

Running high like that indicates too much air. With the enrichment circuit (choke) on, extra air/fuel is delivered. But i'd almost suspect a leak in the body somewhere... Hmmmmmmmmmmm.

I'm going to have to go think about it.

By the by, the reason i'm asking about the needle jets is that they're almost identical visually. You haven't really specifically said "yes, i read z-x off the side of the needle", you've only given descriptions that could apply to new jets, or cleaned old jets, or whatever, and you could call "taking it apart, USC'ing the brass, cleaning the bodiess, putting it all back together" a rebuild.

Sorry for being/seeming pedantic. But it's the little things that are going to nail you.
 
Okay. Hm. I'm going to assume that your carbs are fairly close to balanced, and that you've actually visually ensured that the butterflies are totally closed. Because if they're off balance, that would explain that behaviour totally.

Yes, visually they are balanced and close completely. Same way I did the other carb. I have done about 4 other 76-79 carbs.


Running high like that indicates too much air. With the enrichment circuit (choke) on, extra air/fuel is delivered. But i'd almost suspect a leak in the body somewhere... Hmmmmmmmmmmm.

Yes, agreed, however I am at a loss.

I'm going to have to go think about it.

By the by, the reason i'm asking about the needle jets is that they're almost identical visually. You haven't really specifically said "yes, i read z-x off the side of the needle", you've only given descriptions that could apply to new jets, or cleaned old jets, or whatever, and you could call "taking it apart, USC'ing the brass, cleaning the bodiess, putting it all back together" a rebuild.

The numbers all match the stock xs650c carb (I verified them). I took everything off and cleaned them. Yes to the Z-8 needle.

Not a true rebuild as you have stated as I have not replaced the parts in a rebuild kit. The bike is in amazing shape with only 5800 miles. All of the replaceable parts looked to be in fine shape, thats why I did not replace them.
 
On your pilot jets The 78-79 carbs are set up different. The 76 carbs draw air from below the jet , the 78-79 carbs draw air at the top of the jet. If any mix up the pilot circuits won't work right.
Some of pilot jets have large holes in the sides of the jet, these aren't as important as the actual jet hole that goes the long way of the jet.
One jet the orifice that meters the fuel is next to the threaded area, the other is at the tip opposite the threads, If the orifice isn't clear the idle circuits won't function.
I know this may seem to be a simple matter but often overlooked.
Another thing to check for on a hanging idle is your ATU, advance timing unit.
If it is sticking in the advance position it can cause a high idle.
To check, you gently pull the advance weights apart and quickly release, they should snap shut. If not you need to remove the rod, clean the rod and bushings and seals, regrease the parts and reinstall them and recheck the snap back. If it still won't snap back the rod may need to be polished where it rides in the bushings. Crocus or fine emory cloth will work.
 
xsLeo,

I did them separately so there is no mix-up on the parts (I verified them again). All passages are clean as well.

The ATU seems to be fine as the 78 carb is on the bike now and it runs really good...
 
Have you done a float level check? kind of hard to do an actual gas level with those brass float carbs. Might be no gas into the running circuits is the problem area? One (kind of) simple method would be to drain the float bowls of these and a different set of known good brass float carbs and compare.
just to be clear it sounds like it probably leans it's self out not chokes it self out when you release the (enricher) choke.
 
As some one else said on another thread, "Your carbs are cursed, bury them in consecrated ground and pray over them." or something to that effect. Occasionally you get carbs that just won't work.
Have the 76 carbs ever ran for you? Or is this a recent acquisition? If a recent acquisition maybe they are the reason it's now yours.
I assume the 78 set is from another running bike.
If so, you might want to get another set to try.
 
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