The air "bleeds" are what I have labeled as the air feeds in my pic. They come from the two air jets on the outer edge of the intake bell, shown at 4 and 8 o'clock in your 1st pic a few posts up. Note in your pic the air jet on the left labeled "M". That feeds the main and needle jet. The unlabeled jet on the right feeds the pilot circuit.
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Bike runs good until it's warmed up, then terrible
- Thread starter Rexxis
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- carburetor engine
Rexxis
Almost there...
Z-8 needle jets and the needle says 4m1.
It also appears you may have some of your carb top screws in the wrong locations. The longer screws are used in the inside holes through the butterfly shaped bracket. Yamaha cheaped out here. They should have given you 5 longer screws because the throttle cable bracket requires one too. They only used four. I swap that incorrect screw out for a longer one so I get full use of the limited amount of threads offered. Tightening a too short screw into 2 threads of aluminum is just trouble waiting to happen.
Rexxis
Almost there...
Plungers look good and float needles check out good.
Slides(JBM diaphragms)
Slides(JBM diaphragms)
I have to ask - were you running these carbs as pictured in your 1st pic in post #49? If so then therein lies the problem I think. The cutaways in the slides aren't aligned properly, in fact one looks as if it's in backwards. Note the small bleed hole through the flat part of the bottom of the slide in your pics above. That should face straight ahead towards the motor and the angled cutaway should face straight back toward the air filter.
Rexxis
Almost there...
Yep, it was but i don't believe it ever made it in the bike like that. I just realized that when I pulled my needles. The bike had the same issues before and I know they were in properly then.
I think I need more workspace.
I think I need more workspace.
Just looked at slides in post #49. Haha, good catch 5twins.
I sure hope you can help sort out his carb parts, mix/match here is beyond me...
I sure hope you can help sort out his carb parts, mix/match here is beyond me...
Rexxis
Almost there...
As far as I can tell(read), everything seems correct. Even checked needle jet and needle to carb spec sheet and they are correct as well
I went ahead and printed out the Amckay guide bc I got tired of trying to look at it on my phone out in the shop.
I went ahead and printed out the Amckay guide bc I got tired of trying to look at it on my phone out in the shop.
Yes, the needle and needle jet are correct for the '76-'77 carb set but what I was concerned with was if the needles are fitted into '78-'79 slides. I really don't thing that would work right. Do your needles mount as illustrated above or like this ? .....
The 4M1 needles are 5mm shorter than the 5O2's used in the '78-'79 slides. Mounting 4M1 needles in these later slides would have them riding 5mm higher and be very, very rich.
The 4M1 needles are 5mm shorter than the 5O2's used in the '78-'79 slides. Mounting 4M1 needles in these later slides would have them riding 5mm higher and be very, very rich.
Well, looks like you've got the `76-79 bowl, `76-78 needle/jet combo, what about carb body?
Rexxis
Almost there...
Mechanic at the local shop put those on there. I'd ask if they have any at a shop. Take that picture with you or they may try to act like your crazy. That's how most of the shops I've been to like to act, as if you're an idiot.
Twins, My needles mount like shown in the second picture.
Twomany, '76-'77 body. See post #6 here: http://www.xs650.com/forum/showthread.php?t=23881
Bowls are '76-'77 bowls bc they have the nipples on the bottom. See, I'm learnin!
Bedtime guys, will resume in the morning.
I can't say thank you enough, very much appreciated!!
Whew! My head's a-spinning. Reread 5twins carb booklet. Suddenly it hit me like a ton of bricks.
In late `74-75 H*nda cut over to 'epa' carbs. That was a nightmare, and all those memories swept over me.
We were introduced to new terminology, new procedures, including a fixed jet 'no touchee' policy.
Bikes idled like crap. Upset customers/salesmen/mechanics, whotta nightmare...
Had no choice, had to crack open some carbs, pry-off sealed covers, drill-out jets, modify bleeds.
And ...and ...and (stop it, you're digressing, or regressing)
Rex, 5twins - You guys are doing a great job nailing this down. I'll watch as you sort this out...
In late `74-75 H*nda cut over to 'epa' carbs. That was a nightmare, and all those memories swept over me.
We were introduced to new terminology, new procedures, including a fixed jet 'no touchee' policy.
Bikes idled like crap. Upset customers/salesmen/mechanics, whotta nightmare...
Had no choice, had to crack open some carbs, pry-off sealed covers, drill-out jets, modify bleeds.
And ...and ...and (stop it, you're digressing, or regressing)
Rex, 5twins - You guys are doing a great job nailing this down. I'll watch as you sort this out...
Thanks 5twins sure glad you stepped in.
When I first saw rexxis carb bodies I could not quickly find a good write up on matching up the components. I know 5T has posted a bunch of good pics showing difs several times, but a carbs through the years illustrated guide is not in tech yet. As more and more of the OEM carbs get taken apart boxed and shuffled this will be a recurring issue. I have it myself I have an (um) collection of carbs of all years mostly complete sets but boxes of random parts also. It is very easy to mix and match parts that won't play nicely.
I have a set of non CV CB650 carbs on the bench now and I hate messing with carbs I don't "know" like XS650 carbs. I cannot quickly ID where carb cleaner should and shouldn't go when blowing passages so am left wondering if I have blockages or it is "as designed"
When I first saw rexxis carb bodies I could not quickly find a good write up on matching up the components. I know 5T has posted a bunch of good pics showing difs several times, but a carbs through the years illustrated guide is not in tech yet. As more and more of the OEM carbs get taken apart boxed and shuffled this will be a recurring issue. I have it myself I have an (um) collection of carbs of all years mostly complete sets but boxes of random parts also. It is very easy to mix and match parts that won't play nicely.
I have a set of non CV CB650 carbs on the bench now and I hate messing with carbs I don't "know" like XS650 carbs. I cannot quickly ID where carb cleaner should and shouldn't go when blowing passages so am left wondering if I have blockages or it is "as designed"
I don't quite have all the info I need for a complete carb I.D. write-up yet. There are a couple of the carb sets I've never actually even seen and my knowledge of them comes from what I've been able to gather off the net and from manuals. Some day though, I'll lay hands on these.
OK, so it's official - you have complete '76-'77 carbs, including the slides. That rules out the slide/needle mismatch factor. The only couple things I have left to suggest are a bad (worn) needle jet in that left (rich running) carb or maybe the mains are too large. You could try switching the needle jets from carb to carb and see if the rich condition follows. You could also try 132.5 and 130 mains to see if that helps. Although that doesn't explain why one carb is rich, the other lean. They shouldn't be that way with the same jetting. Which leads me back to what I mentioned earlier - maybe one carb is just plain bad, buggered up internally somehow.
OK, so it's official - you have complete '76-'77 carbs, including the slides. That rules out the slide/needle mismatch factor. The only couple things I have left to suggest are a bad (worn) needle jet in that left (rich running) carb or maybe the mains are too large. You could try switching the needle jets from carb to carb and see if the rich condition follows. You could also try 132.5 and 130 mains to see if that helps. Although that doesn't explain why one carb is rich, the other lean. They shouldn't be that way with the same jetting. Which leads me back to what I mentioned earlier - maybe one carb is just plain bad, buggered up internally somehow.
Like gggGary said about blocked passages, we had a set of 'epa' carbs that, without warning, started appearing with a new passage plug. Pharmacy ran outta aspirins that day.
Although they don't clog up that often, I suppose it's worth checking those air jets on the bellmouth. That one marked with the "M" feeds the needle/main jet. With the needle jet removed, spray carb cleaner in the air jet and blow it through using compressed air. It should come out through the side of the bored hole through the body that the needle jet sticks into and out one of those air feeds on either side of the needle jet on the carb body bottom. The pilot air jet will come out the other one.
Essentially, as it was explained to us at H*nda, there were the 'pre-epa' carbs and then the 'epa' carbs, with 2 different idle circuit methodologies.
The older/original 'pre-epa' carbs premixed bleed air at the pilot jet, which then went to the 'idle' screw. That screw controlled total idle fuel flow.
The later 'epa' setup changed that, so that the screw now controlled how much bleed air went to the pilot 'percolator' or 'aerator' (part of pilot jet with lateral holes), hence was now called the 'mix' screw.
These new 'mix' screws had rotation-restriction caps on them, to maintain compliance.
It never dawned on me that the other brands were going thru similar nightmares, now with 5twins docs/diagrams I can see Yamaha had similar design changes. The H*nda changes were primarily in the carb body, bowl swap was often not a problem. The Yamaha BS carbs, with the critical jet/mix zone in the bowl, have to have proper body/bowl match. Then, as 5twins shows, a different slide arrangement appears in this timeframe. I believe GggGary's spot on with his 'recurring issue' prediction.
The older/original 'pre-epa' carbs premixed bleed air at the pilot jet, which then went to the 'idle' screw. That screw controlled total idle fuel flow.
The later 'epa' setup changed that, so that the screw now controlled how much bleed air went to the pilot 'percolator' or 'aerator' (part of pilot jet with lateral holes), hence was now called the 'mix' screw.
These new 'mix' screws had rotation-restriction caps on them, to maintain compliance.
It never dawned on me that the other brands were going thru similar nightmares, now with 5twins docs/diagrams I can see Yamaha had similar design changes. The H*nda changes were primarily in the carb body, bowl swap was often not a problem. The Yamaha BS carbs, with the critical jet/mix zone in the bowl, have to have proper body/bowl match. Then, as 5twins shows, a different slide arrangement appears in this timeframe. I believe GggGary's spot on with his 'recurring issue' prediction.
Rexxis
Almost there...
My feelings exactly.
I blew carb cleaner through the needles on the bell face and everything came out its respective holes. I'm gonna be buttoning the engine back up today. Hopefully I can get to carbs tomorrow and give them a seriously good "once over."
