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Carb questions from another new guy! - New (to me) 78 cs650

Discussion in 'The Garage' started by Kubes42, Jun 8, 2020.

  1. Kubes42

    Kubes42 XS650 Member

    Hey there, another new guy with more carb questions for those of you who aren't sick of them yet!

    Heres the story.

    Purchased a 78 xs650 with about 9000 miles that was kept just outside of the D.C. area, and brought it down to Mississippi. Bike is super clean, new gaskets just about everywhere, general tune up, new tires, carbs were cleaned, new spark plugs, updated rear suspension, the list goes on... Previous owner bought it, spent a lot of money for a custom bike shop to make the repairs and light modern mods before realizing he wanted a more modern bike as he didn't know how to do any work himself and didn't want to spend so much money at the shop haha. The previous owner has the receipts, and I also called the shop before buying just to get their opinion on the bike as a 3rd party. They said it was in great shape, only thing left to do was potentially re-jet if you really wanted it to be perfect, but that it ran great . I was anticipating some minor changes to the carbs, as it was last tuned for Washington D.C. winter weather...not exactly 95 degrees with 95% humidity currently here.... So I was sold knowing a little work would have to be done!

    Got the bike down to hot and humid Mississippi and got her idling, but just barely. Requires choke and prime if it's been sitting cold. Lots of pops from both the exhaust and the carbs. Sometimes pops and sputters itself dead. Sometimes revs itself over 3k and gets stuck there. Also if I rev it, it will sometimes hang at 3k (sign of running lean?). Cannot get a consistent idle RPM to settle to, it goes between those two with no rhyme or reason. Fresh gas. New spark plugs (that are coated pretty black after even short idle sessions...sign of running rich?). Previous owner had the fuel mixture screw turned waayyyy out. like 6-7 turns. Practically falling out haha. I turned it back to about 2, and the headers got red hot within 3-5 min of idle (due to leaning it out?). Backed it back out to about 4 turns and they still seem to run hot, but not red hot in 5 min...

    figured ok, well this bike has cheapo air filter pods (new uni ones on the way) and a 2-1 delkevic exhaust on the right side, I should go ahead and re-jet it for the change in airflow and climate, thinking its probably running lean based on the super hot pipes, increased aftermarket air flow, hanging idle, fuel mixture being way open...but kind of confused about the spark plugs showing a rich condition, sometimes bogging down and dying at idle, and climate (hot and humid would mean less dense air compared to DC winter = actually helping run less lean than before?) all showing maybe a rich condition.

    I opened up the bs38 carbs expecting to see stock jets. They were as clean as new which was comforting at least. But...rather than stock, there was a pilot of 35, and a main of 155! I was planning on trying a pilot of something like 30/32.5 and main of 140-145...So I was shocked to see jets much larger than what most people are running/recommending (from what i can see anyways, again im pretty new here). I have not been able to get the bike past my driveway since the idle has been so inconsistent, so I cannot speak to how it runs when operating on the mid and upper ranges of the carbs. The 35 pilot jet seems too big, but not crazy. But would running a 155 main jet cause such issues at idle? I know the phases blend together a bit, but seems like I haven't even gotten to run the range where the main would come into play.

    I guess my question is, am I just miss diagnosing the lean condition, and its actually super rich? the potential indicators for both conditions is throwing me off a bit. Ive read the carb guide and lots of other posts, and found it super helpful. I still plan on trying my planned jets listed above either way, unless there are some suggestions out there! Please let me know if I have a critical misunderstanding of whats going on, this is my first real attempt at this kind of thing. So far Ive learned a good amount just by reading and watching, but I have a long way to go in real world application.

    Thanks for your help!
    Last edited: Jul 3, 2020
  2. grizld1

    grizld1 Grumpy old man Top Contributor

    Once again: troubleshoot ignition first.
    lakeview likes this.
  3. stinky78

    stinky78 XS650 Addict

    welcome to the forum! like the grizld one said check your ignition is all good first, there is no point pulling your carbs apart and trying to get them right if they aren’t the issue, start with the easy things first, you need to know that your bike is otherwise in tune before you tune your carbs or you’ll never get it right, so adjust your cam chain, check the condition of your plugs, make sure you have a spark on both sides, check your ignition timing, then read the carb through the tech section of the forum and find the the excellent write up that a generous and knowledgeable member did, then read it again! then get stuck in to your carbs,. but I’d guess the “custom bike shop” didn’t re-jet after adding the pods and exhaust, or they tried to re-jet it and just couldn’t get it to run right.

    aside from all that you might still find it’s an uphill battle tuning your CV carbs with your 2into1 exhaust, I’d be inclined to either fit a 2into2 exhaust, or if I was super attached to the Delkovic update to some more user friendly carbs like VM34 or 36s

    oh and don’t believe anything previous owners or bike shops tell you, most “custom bike shops “ know Harleys and not much else, so unless they specialise in old Yamahas or something they probably don’t have any specific knowledge of your bike.
    lakeview likes this.
  4. Kubes42

    Kubes42 XS650 Member

    Thanks, So far I have adjusted the cam chain (was just a tiny bit loose), plugs are brand new, solid spark on both sides. I'll be honest, I gotta do some research on checking the timing myself, I have never done that! But before moving the bike down here to Mississippi, it did not have these issues in any sense, so im guessing the timing is fine? But better to know than assume, so I'll get on that while waiting for some other parts to come in. After the carb guide...again haha.

    Yeah the bike already had the exhaust and air pods on it and what seem to be overkill re-jetting when the previous guy bought it. The shop said they just cleaned the carbs, did not make any adjustments to the jets for him. It ran a little on the rich end, but the previous owner didn't have any issues big enough for him to want to pay them to adjust it.
    (he bought with all the mods done on it, had it for about 6 months and realized he didnt have the time/knowledge to work on it, and didnt want to keep paying to always tinker with an older bike, so I bought it from him to learn how to work on it, and he got a more modern bike).

    Have a lot of people run into issues with 2-1 exhaust? Im not dead set on that style, other than its what the bike has on it, and not spending more money buying new ones would be cool haha. It does sound really nice though!

    Good point on the shops, especially cause i didn't work directly with them, it was all relayed over the phone.

    Id be curious to know if anyone else is running 35 pilot and 155 mains? most people seem to be in the 30 and 140 ish range from what I can tell?
    that just seems excessive to me in my limited reading as im just getting into this bike!
  5. 5twins

    5twins XS650 Guru Top Contributor

    Yes, the ignition needs to be right but I'm going to say your carbs are way over-jetted too. I remember trying a 150 main in my '78 carbs when I first got it. I got to the end of my street and turned around because the bike was running so bad. Checked the plugs and they were blacker than a moonless night, lol. 155's may be worse. 35 pilots are probably too big as well. I would suggest 30 pilots, or 32.5 at most, and 140 mains to start. You'll also need to lean the needles a step to the #2 slot (from the top). It's very easy to over-jet CV carbs and still have the bike run. These carbs work on engine demand so will still operate with jets that are too large. The slide simply won't lift all the way so the large main won't flow at it's max rate.

    Initial mix screw setting for that carb set is 2.25 turns out. It should dial in pretty near that even with slightly larger pilot jets.
  6. Kubes42

    Kubes42 XS650 Member

    5twins, good to hear. Those are the sizes I’m waiting on in the mail (plus a few sizes close to that) after reading a lot of other people’s adjustments. A lot of which were based on your inputs, so thanks for chiming in so fast!

    Hopefully I’ll have it sorted out by this weekend if the parts get in on time. The more info you guys have on this stuff the better, I’m just trying to soak as much of it up as I can.
  7. nj1639

    nj1639 Paleo-simplistic Top Contributor

    No fan of 2 into 1 here. 2 carbs and 2 cylinders should have 2 exhausts......plus the symmetry.
    I like to be able to feel the individual cylinders pulses when tuning and troubleshooting.
    Machine and Kubes42 like this.
  8. stinky78

    stinky78 XS650 Addict

    agree with al of the above with the added comment that 2into1 headers tend to mess with CV carbs, the best I can explain it is that you get weird out of time pulses coming back through the inlets, making them hard to tune, due to the simple fact that the V in CV stands for vacuum, maybe someone else will put it more eloquently than me.
    gggGary and Kubes42 like this.
  9. GLJ

    GLJ Never go faster than your guardian angle can fly. Top Contributor

    Starting with the jet sizes 5t suggested is a good place to start. As grizled1 said check the ignition. If the advance is sticking and/or over advancing that will cause a lot of seemingly carb related problems.
    gggGary and lakeview like this.
  10. Bushyeyed1

    Bushyeyed1 Cafe Racer Top Contributor

    If you had a cdi and BS34s I could probably help you get your 2-1 dialed in pretty close . There is a benefit to a 2-1 but it is very hard to tune for if you don’t know what your doing. On my bike with BS34s it Wouldn’t run right without the Heiden needle / Heiden mix screw and figuring out the right jets. Your lean type symptoms could be your carbs incorrectly sync’d and with a 2-1 you will need a sync Vacuum guage to get it set correctly. Once you get your carbs settled down check out this thread. http://www.xs650.com/threads/heiden-dyno-tune-needle-jet-kit-from-mikes-xs.17263/
    Last edited: Jun 9, 2020
    gggGary likes this.
  11. lakeview

    lakeview XS650 Guru XS650.com Supporter Top Contributor

    Welcome! Some pictures of your bike will please those of us who can only offer moral support...
    Mailman and gggGary like this.
  12. grizld1

    grizld1 Grumpy old man Top Contributor

    Kubes, the shop said it ran fine, but did you ride it? If not, most won't admit that they charged a bunch of money and put the bike out the door running badly! Your E-model (1978) left the factory with breaker point ignition and mechanical advance governor (AKA "automatic timing unit," AKA "ATU"), and both points and ATU are wear items. If that's what you have I'd recommend that you unplug the points wires, inspect the points for pits and corrosion and remove same with a points file or 320 to 400 grit abrasive paper, clean the points with a bit of alcohol on a dollar bill, set points gaps, and inspect timing with an ohm meter. Ground one ohm meter probe and clip the other to the points wire connector. Ignition fires when the points open, so you watch for the meter to show no continuity as you turn the engine by hand and watch the timing marks. Inspect at both idle and full advance. If you can't set the full advance timing without excessive retard in the idle mode, the ATU needs attention: a few searches will turn up a few fixes, but be sure that you don't try to recurve the ignition by bending in the tabs on the ATU rotor. You might go 100 miles before it happens, but you'll find yourself on the side of the road with a dead motor and a rotor tab lying loose in the ATU housing.

    Static timing should get you close enough to start on jetting. When you have a clean idle, finish timing adjustment with a strobe. Good luck, and keep us informed!
    Last edited: Jun 9, 2020
    Kubes42, Team Junk, nj1639 and 2 others like this.
  13. Kubes42

    Kubes42 XS650 Member

    Alright guys thanks for all the help so far on my first bike, it has been super helpful! Significant progress has been made, but it's not there just yet.
    Here is where we are after a few days waiting on parts, and a whole lot of learning!

    -cam chain adjusted to be flush
    -Points cleaned and set to .012 (on the smaller gap size because they are not new, but were in great shape)
    - Advance clean and functioning correctly
    - timing set with an induction light. Right side is about 1 degree "retarded" from the "F" mark. Left is about 1 "advanced" from the F, both inside the limit marks. Spent a couple hours micro adjusting and thats the best I could get haha. Both hit right on the advanced mark at about 28-3000 rpm.
    - carbs are super clean (previously cleaned by shop from the previous owner, verified when I took it all apart myself)
    - Floats set to 24mm (measured from where the base of the gasket would sit, can someone correct me on this if its wrong?)
    - Pilot jet from a 35 down to 30
    - Main jet from a 155 to a 140
    - Needle leaned from the 3rd spot to the 2nd.
    - fuel control screw turned to 2 1/4 turn
    - Sprayed carb cleaner on carb connections looking for leaks, nothing stood out to my untrained ear.
    - Spark plugs are not coated black after running them anymore
    - Still waiting on the Uni pods to replace cheapo knockoff pods. Should help with airflow into the carbs from my understanding
    - still the 2-1 exhaust
    - Have not balanced the carbs myself yet (but they seem pretty close?), planning on doing that once I go pick up a gauge.

    The bike starts right up using either the kick start or electric, a quick choke helps on the first start of the day, but after that no choke needed in this summer heat. It will hold an idle without dying, and without 90% of the backfire that it had previously, although still maybe one or two pops every couple minutes. Will die if I push the choke lever down after engine runs more than a minute or two.

    With a warm engine, the bike seems to surge +/- 800rpm at idle, sometimes peaking at 2k. Took it around the block and 50% of the time it pulls smooth to 4k rpm, other 50% of the time it coughs and lunges 2-3 times between 1500-4k rpm, but continues to run. only tried 1st-3rd gear and only up to about 4k rpm. Headers still seem to run a bit hot, just ever so slightly red after about 15 min at idle and 30 min of testing at 10-40mph.

    Assuming the carbs are balanced correctly, and the same conditions still exist, where would you turn to help settle the idle and address the lunging issue? I have a few other jet sizes I could try, but before just going for it, I wanted to get a better feel for the bike, and ask the wise internet world...since I don't have a great reference on what a "perfect" (or close to it), running xs650 should feel like. I just know it shouldn't lunge while riding. Id expect some idle variations but not sure what is considered a "normal" range when set for a 1200rpm idle. Worth trying a step up on the jets? Is that a symptom of imbalanced carbs? are there a few other things I could try first if I find that verifying the carbs are balanced doesn't help?

    Last edited: Jul 3, 2020
    gggGary likes this.
  14. 5twins

    5twins XS650 Guru Top Contributor

    Yes, you could try 32.5 pilots. They worked well for me before I went through my topend and did some minor porting. After that, I had to go back down to 30's. I had heard that improved flow sometimes required downsizing the jetting slightly and I guess that's what happened, at least for the idle circuit. I had to go up one more on the mains.

    Yes, get the carbs synced exactly if possible. Being out of sync can cause popping and may be contributing to the wandering RPMs.

    These are really nice running bikes once you get everything dialed in correctly. They start easy, idle nice, and should rev freely to red line with no sputters or misfiring. It will take some tinkering. Everything needs to be set right (valves, timing, points gaps, carbs).
    gggGary likes this.
  15. grizld1

    grizld1 Grumpy old man Top Contributor

    "Cheapo knockoff pods" can cause a lot of grief. Some have a stop in the flange that can block the air jets in the intake bell. As 5t notes, synch error can cause hanging idle, but it can also occur if the ignition isn't retarding correctly. I've never seen a shop touch that particular job, so I'd give better than even odds that the advance rod is dry, unless you lubed it yourself.
    lakeview likes this.
  16. Kubes42

    Kubes42 XS650 Member

    Any tricks/advice on lubing the advance rod? or major errors to avoid? I'll add that to my list of things to check!

    5twins: I'll get them balanced this week and the new air filters installed see what happens before trying the 32.5 pilot.

    back with updates as soon as I can!
  17. 5twins

    5twins XS650 Guru Top Contributor

    When servicing the advance rod, what you're mostly lubing is the bushings pressed into the ends of the cam that the rod runs in. That means the rod has to come out. Take the 10mm nut and little disc off the advance end of the rod. The advance unit can stay in place as well as the points cam on the other end of the rod. Pull the rod out from the points side. Once the rod is out, you'll see the bushings in the end of the cam. The I.D. of the bushing has grooves cut into it .....


    Those grooves are there to hold grease and keep the rod lubed, so after cleaning them, pack them full of fresh grease. The factory shop manual recommends a grease with moly in it .....


    There's one little "gotcha" to this service. The hole in the advance rod for the little locating pin goes all the way through. That means it's possible to stick it in either side but only one is correct. The other will throw the timing off 180°. The pin should be aligned with the pin on the other side for the points cam .....


    There are alignment slash marks on the advance unit backing plate and the little disc to help you get it right (yellow arrows) .....


    The slot for the alignment pin (green arrow) usually sticks out a little past the nut and washer so you can check that also to verify it's aligned with the pin on the points cam.
    gggGary likes this.
  18. Kubes42

    Kubes42 XS650 Member

    Alright I haven't been able to do much the last few days due to work, but i was able to get this video (link below) so everyone can see exactly what is happening! any thoughts? Like I said, it fires right up now which is great! And will idle without dying, still a few pops here and there out of the exhaust, but mostly feeling the random revving while at idle, as well as when riding at lower RPMs. Have not gotten to test it out wide open or higher than about 4k rpms.

    Thanks for your inputs so far!
  19. Kubes42

    Kubes42 XS650 Member

    Back with some updates!

    After some frustration dealing with what can be seen in the video above, I decided to go back to the basics. (cause thats about all I know haha)
    Fuel? Check.
    Air? check.
    Spark? visual spark checks on both sides...But figured "let's pull the spark plugs just to see how they look, cant hurt right?" Left now looks to be running pretty optimal, good progress after the rejetting!! the right...well shoot, super rich with the same exact changes made from the left side. Leads me to think the right is acting up. I plug it all back in, and the bikes random revving "pulses" from the video are gone...Could it really be that simple? A loose spark plug cap? Sure enough, I fidget around with it a bit, and get it to sit a little off center, and the revving and backfiring comes right back. Seat it back nice and snug, calms right down. Looks like a new spark plug cap that doesn't bounce around is on the way!

    Now here is where I could again use some help learning!
    I went to play a little with the mixture screws using the "dead cylinder method" and discovered when I pull the spark plug cap off the right side plug (that I had just been fidgeting with), the bikes left cylinder runs just fine. But when I go plug the right side back in and pull the left plug cap, the bike instantly dies. It cannot stay running with just the right cylinder.

    I should be able to run this dead cylinder test on either side correct? the right side should be able to run with the left plug disconnected? Just like the left side ran just fine with the right disconnected...Am I missing something obvious here?

    My instant panic brain combined with lack of knowledge jumps right to a major compression issue on the right side, or something requiring the entire engine to be pulled and rebuilt...something I don't want to do. Hoping you guys can talk me off that ledge... or you can confirm the worst case possibilities and I can deal with the pain at least knowing i having a solid answer haha.

    Lets assume the new spark plug cap arrives and I still have this issue of the bike dying when the left spark plug cap is pulled...Where would you guys recommend I start trouble shooting so I can effectively run the dead cylinder method for setting mixtures on the right cylinder carb without the bike dying?
  20. gggGary

    gggGary When a whole one is just too much. XS650.com Supporter Top Contributor

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