1. Dismiss Notice
  2. Hey Facebook people... We've created a group for XS650.com members to connect. Check it out!
    Dismiss Notice

Hovering/ high idle

Discussion in 'The Garage' started by Bufoalvarious, Jul 20, 2019.

  1. Hello everyone. I've made a couple posts on here but I'm stuck again! I have a 79 special with b38 carbs and I was having issues with the engine breaking up between 2k and 3k (pods and no baffles) which was solved by adjusting my needle level to give me a bit more fuel (already replaced MJ and PJ) and now the bike is not having any issues with that. BUT AFTER warming up and riding around a bit it will hover at 2k when in neutral. I ease the clutch out a bit and the rpms will drop below that point then begins to idle fine again. If I am riding, while decelerating it will not hover around that point. I sprayed carb cleaner on my boots and nothing special happened. Let me know if you guys can think of anything.
    Stay safe.
     
  2. Note that it has "stock" spark plugs. They are new but they are the blah blah 7e something or another
     
  3. 5twins

    5twins XS650 Guru Top Contributor

    18,777
    9,542
    688
    The bike is a '79 but are the BS38 carbs on it a '79 set as well? You say you changed the main and pilots, but from what to what? Normally with a '79 carb set and mods similar to yours, you would go up one or two sizes on the pilots, two or three sizes on the mains, and lean the needles a step. If you've only gone one up on the pilots (27.5 stock to 30), you may need to go another to a 32.5. This size is a recent offering from Mikuni so may not be listed everywhere. The sizes used to jump from a 30 to a 35. A 35 would probably be too much so I wouldn't go there.

    You'll also want to make sure your mix screws are dialed in properly. Stock spec for the '79 carbs is 2.25 turns out. Re-jetted, you'll probably still end up near that, somewhere in the 2 to 2.5 turns out range.
     
    lakeview and timbeck like this.
  4. Yes. The carbs are 79 b38 carbs. Both jets have the double square Mikuni label next to the number MJ is 142 and my pj is 45.and my needle clips have been moved down one fixing my rpm breakup between 2k and 3k which work wonders until the bike it warmed up then it will "hang" at 2k before dropping. I tried adjusting my mixture screws WHILE it was stuck in the 2k area. And turning them in causes rpms to rise but I can almost back the mixture screws all the way out with no change. Maybe a smaller Pj? Ive tried the carb clean on the boots and nothing. I'm going to bench sync my barbs later today. I see that you're pretty much the guys to talk to on this forum 5twins so I appreciate all the help you've given me. I've searched keywords and looking at very similar threads and cant seem to find my issue as easy as others.
     
  5. I also live at 5k feet above sea level. I've read it matters but I dont know.
     
  6. Waaait. So is it "hanging up" because I have too much fuel now? Or is it lack there of.
     
  7. 5twins

    5twins XS650 Guru Top Contributor

    18,777
    9,542
    688
    Yes, a 45 pilot jet would be way too big. You may also have gotten the wrong type. Two types of pilots were used in these carbs over the years, the VM22/210 and the BS30/96. Externally, they are very similar and will actually interchange, but internally, they are different. They flow differently. The various carb sets used over the years of 650 production were designed to use one style or the other. Your '79 carb set was designed to use the VM22/210 style.

    [​IMG]
     
  8. It is the vm 22 type. And I'll pick some smaller ones up and give them a try I guess. The bike runs amazing and will always run through the gears with no issue. Its just when I pull up to a light the bike will try to hang at 2k. I trust you when you say that my PJ is too big but would that make it "hang" momentarily or do I have more issue than I think?
     
  9. 5twins

    5twins XS650 Guru Top Contributor

    18,777
    9,542
    688
    It could be that way too big pilot. Like I said, that's way, way bigger than normally used. Usually you only go up 1 or 2 sizes from stock, from a 27.5 to a 30 or 32.5. 35 usually proves too big so that 45 has got to be way off.

    Yes, there is another possible issue, your advance assembly. It may be hanging up or sticking and not allowing the timing to return to the retarded position. That would make the revs hang. Have you serviced (lubed) the advance rod that runs through the cam in the head? You have to keep the ends greased so it turns easily.
     
    lakeview likes this.
  10. Thanks for all the help! I'll order some new jets and research on my advance assembly
     
  11. 5twins

    5twins XS650 Guru Top Contributor

    18,777
    9,542
    688
    Looking at the pics in your other thread, I see a couple things off with your left carb .....

    [​IMG]

    First, I think you have the return spring on the butterfly shaft installed backwards. That large loop should be to the inside and fitted onto a post sticking out from the side of the carb body. There is a much smaller hook that fits on the cable arm .....

    [​IMG]

    [​IMG]

    Next, the detent bracket for your choke lever is bent up pretty badly. It should run pretty much horizontal so the choke lever can ride over the top of it. Your choke lever end is bent too .....

    [​IMG]

    The improperly fitted return spring could be contributing to your hanging idle speeds. Maybe the spring doesn't have enough tension to do it's job like that.
     
    TwoManyXS1Bs likes this.
  12. JESUS SOME PEOPLE! THANK YOU SO MUCH I WOULDVE NEVER NOTICED. As I've said I bought this for $200 in bunch of boxes and it my first bike. And I'm trying to recover from the precious owner. Hense the 45 PILOT JET!?
     
  13. 5twins

    5twins XS650 Guru Top Contributor

    18,777
    9,542
    688
    Well, at least you got it up and running. Now it's just a matter of refining things, making everything right and as it should be. They work and run best like that, lol. This is a very nice bike, easy to work on, and a good "teacher". Yes, it's rather "old school", but that will teach you some of the "dying arts" of motorcycle mechanics, things like adjusting valves and setting points/timing. You'll also be learning about carb tuning.
     
    TwoManyXS1Bs and lakeview like this.
  14. Let's see if this helps at all. Right side was normal. Also removed after photo and gave it a nice clean
     

    Attached Files:

  15. 5twins

    5twins XS650 Guru Top Contributor

    18,777
    9,542
    688
    That's looking better. Keep chipping away at it, you'll get there eventually. Don't forget to inspect your advance unit, I'm sure it needs some T.L.C. Most haven't been touched or serviced since they left the factory 40 some years ago.
     
  16. So the spring wasn't the issue. I tried adjusting my A/F screws and it left me stranded unable to get the bike even running again. I'm going to change the PJ asap. The advancement unit seems very complicated. Any links to a simplified explanation?
     
  17. At 2 1/2 the LEFT side would run WITH choke
     
  18. 5twins

    5twins XS650 Guru Top Contributor

    18,777
    9,542
    688
    With pilots as large as you have, mix screw adjustments may not help much. You may need to close them up quite a bit, like down to 1/2 or 1 turn out, but even that may not help, the pilots may just be too big. The pilot jet flows it's fuel/air mix into the main bore through 4 tiny holes. Three are clustered together at the top of the bore and come directly from the pilot jet. You have no control or means of adjusting how much comes out of them. The fourth hole is off to the side and flows to and by the mix screw. You can adjust how much comes out this hole with the mix screw. But, as you can see, this gives you the ability to adjust only about 25% of the flow from the pilot jet. Also, this doesn't change the strength or mixture ratio of the fuel/air mix, just the amount. To change the mixture ratio, you need to change the pilot jet size.

    [​IMG]

    With 45 pilots, I'm thinking your mixture strength or ratio is just too rich, and turning the amount down by 25% probably isn't enough to compensate for that.
     
  19. Hey 5twins I'm not sure if you'll end up seeing this but my bike won't even try to start 1 turn out. I know that after around 3 nothing is happaning but that is where it starts to cough and splutter (but start) then die. My spark plugs are super black and sooty which mean I have to much fuel but when my af screws are turned down nothing happened at all. I bought the spark plugs last week
     
  20. 5twins

    5twins XS650 Guru Top Contributor

    18,777
    9,542
    688
    I really don't think you're going to get anywhere until you get the right size pilots. You also mentioned raising the needles? That's probably making the situation worse as that is a richer setting. The usual routine is to increase the mains and pilots, but only by a few sizes at most, and LOWER the needles to lean the midrange out. Bigger mains and pilots bleed over into the midrange and make it richer too, usually too rich. You fix that by lowering (leaning) the needles a step.
     

Share This Page