1. Hello Guest. You have limited privileges and you can't "SEARCH" the forums. Please "Log In" or "Sign Up" for additional functionality. Click HERE to proceed.

82 XJ Maxim Vacuum Hose

Discussion in 'XJ Technical Chat' started by Xjnick, Mar 23, 2019.

  1. Xjnick

    Xjnick Member

    Messages:
    30
    Likes Received:
    4
    Trophy Points:
    8
    Location:
    Arizona
    Need some help.
    With the vacuum hose hooked from the petcock to carb #3 port, I didn’t get anything with the petcock on “on” or “prime” position. It would sputter and try to start and backfire when the vacuum line was pulled from the petcock and my thumb covered one end. Also wasn’t getting any fuel with the petcock set to “on” but was when the petcock was on “prime.”
     
  2. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

    Messages:
    14,626
    Likes Received:
    5,008
    Trophy Points:
    113
    Location:
    near utica, new york
    Time for a petcock rebuild, but verify that your vacuum tube isn't plugged or collapsed
     
  3. Xjnick

    Xjnick Member

    Messages:
    30
    Likes Received:
    4
    Trophy Points:
    8
    Location:
    Arizona
    I'll check out a petcock rebuild kit... I know the vacuum tube isn't plugged. Is it pretty noticeable when it's collapsed?

    Shouldn't it at least start up since i'm getting fuel when petcock is on "prime" ?
     
  4. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

    Messages:
    14,626
    Likes Received:
    5,008
    Trophy Points:
    113
    Location:
    near utica, new york
    Well when you said ' it was when it was on PRI' I thought you meant it would start then.... my bad.

    Either way, if you get fuel on PRI (since it is free-flow at that setting) and you don't get any when you are on RUN or RES (where there is vacuum needed to open the petcock), and the vacuum does not seem to open the petcock, it would point to a petcock issue
     
  5. Xjnick

    Xjnick Member

    Messages:
    30
    Likes Received:
    4
    Trophy Points:
    8
    Location:
    Arizona
    Got it. Do I need a whole new petcock or just new seals that come with a rebuild kit? And just to double check... the vacuum hose hooks in to the carb #3 intake boot, correct? Would it be worthwhile to try joining it to one of the other carb intake manifolds?

    It was sputtering when I had it set to prime and it seemed like it wanted to start but I couldn’t get it. Is the vacuum line needed for it to start even when petcock is set to prime?
     
  6. XJ550H

    XJ550H Well-Known Member Premium Member

    Messages:
    13,199
    Likes Received:
    3,854
    Trophy Points:
    113
    Location:
    Great North Woods
    some petcocks are to far gone to rebuild but yes just the rebuild kit.

    Rebuilding the Yamaha Vacuum Fuel Valve w/pics

    If #3 is the open port then yes. Any port you want can be used. use caution with hose routing so you do not end up with a kink.

    vacuum line runs on/run and reserve. prime is a gravity feed

    How much gas do you have in your tank?


    vacuum line is something you would want to replace when you rebuild your petcock. 4mm ID is the size
     
    Last edited: Apr 21, 2019
  7. Xjnick

    Xjnick Member

    Messages:
    30
    Likes Received:
    4
    Trophy Points:
    8
    Location:
    Arizona
    Plenty of gas. I guess my next step is getting that rebuild kit. Thanks guys
     
  8. XJ550H

    XJ550H Well-Known Member Premium Member

    Messages:
    13,199
    Likes Received:
    3,854
    Trophy Points:
    113
    Location:
    Great North Woods
    do you have a vacuum pump brake bleeder? hook a vacuum hose to petcock and fuel line into a container set to reserve apply vacuum and see if you get flow.

    no pump? you can just suck on the hose for the petcock test
     
  9. Xjnick

    Xjnick Member

    Messages:
    30
    Likes Received:
    4
    Trophy Points:
    8
    Location:
    Arizona
    No pump, but that is a handy trick. I'll give it a shot.

    Fuel should also come out when you do the petcock test with the petcock set to "ON" correct? And just to be sure I'm doing this right... the vacuum hose IS hooked up on both ends when I do the petcock test?

    I'd hate to get a good mouthful of 'ol 87 and not have even done the test the right way ;)
     
  10. XJ550H

    XJ550H Well-Known Member Premium Member

    Messages:
    13,199
    Likes Received:
    3,854
    Trophy Points:
    113
    Location:
    Great North Woods
    yes to on as well will work test both

    vac hose goes to the vacuum nipple on petcock
    the fuel nipple goes to a hose to drain into a container do not suck on this fuel hose
     
  11. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

    Messages:
    14,626
    Likes Received:
    5,008
    Trophy Points:
    113
    Location:
    near utica, new york
    Well, yes--- BUT the one end is hooked up to the vacuum port on the petcock and the other end will be hooked up to the s0urce of vacuum.....'whether it is your m0uth, or a one-person bleeder, or the engine intake vacuum port. Either way you should not get any gas in your mouth. If you DO, then the diaphragm is ruptured. The vacuum is on one side of the diaphragm, the fuel is on the other. T he vacuum pulls the diaphragm back to allow the fuel to flow PAST it, not thr0ugh it.
     
  12. Xjnick

    Xjnick Member

    Messages:
    30
    Likes Received:
    4
    Trophy Points:
    8
    Location:
    Arizona
    Gotcha, I had just misunderstood what XJ550H had said earlier. I’ll give it a shot tonight!
     
  13. Xjnick

    Xjnick Member

    Messages:
    30
    Likes Received:
    4
    Trophy Points:
    8
    Location:
    Arizona
    I’m getting fuel in on position. This was confirmed when I did the petcock test you guys mentioned. Got it started, no choke, no gas. Idling Very high. I almost can’t let it idle because it’s as if the throttle is pinned. There is slack in the choke and throttle cable. None of the arms on the throttle linkage are engaged when this was happening (see pic). My only thought is maybe carbs need to be re synced but not sure why it would start that high when the carbs aren’t very out of sync.
    Maybe I should play around with the idle screw, but I don’t think it was tightened very high. At least not enough for it to start that aggressively.
     

    Attached Files:

  14. Xjnick

    Xjnick Member

    Messages:
    30
    Likes Received:
    4
    Trophy Points:
    8
    Location:
    Arizona
    Is there a standard amount of turns the idle screw should be off of a light seat?? Ex: 6 turns off of a slight tight fit, etc.
     
  15. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

    Messages:
    14,626
    Likes Received:
    5,008
    Trophy Points:
    113
    Location:
    near utica, new york
    Idle speed screw gets adjusted to where you want it.

    My first question now is: "can check to make sure the throttle cable and enricher cable have not inadvertently been switched...... throttle to center so it opens butterflies, enricher cable to top rail so it opens enricher plungers"
     
  16. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

    Messages:
    19,613
    Likes Received:
    6,703
    Trophy Points:
    113
    Location:
    The City of Seven Hills
    And push down on the enrichment plungers to see if that drops the idle.

    Baseline for the idle mixture screws is 2 1/2 turns off a soft-seat.

    Baseline for the idle speed screw is done when you complete the bench synch, but may need to be backed off as the bike warms up, and as you complete the running synch.
     
    Chitwood likes this.
  17. XJ550H

    XJ550H Well-Known Member Premium Member

    Messages:
    13,199
    Likes Received:
    3,854
    Trophy Points:
    113
    Location:
    Great North Woods
    idle adjustment screw is the knob that is in the back of carbs between carb 2 and 3. it should be touching and moving throttle linkage to set your idle no soft seat.

    the idle mixture screws are set as k-mow stated . there are 4 of these at front top of carbs


    I am just clarifying the t different items
     
  18. Xjnick

    Xjnick Member

    Messages:
    30
    Likes Received:
    4
    Trophy Points:
    8
    Location:
    Arizona
    Idle mixture screws set properly. The throttle cable and enrichment cable WERE switched. That explained quite a lot. To be fair to me, they were switched from the time I got the bike until about 30 minutes ago. But I should have used common sense and caught that they were hooked incorrectly.

    But, I have some good news for once on this thread! Cold start with the choke on a bit, it fires up! Not having that insane idle issue anymore, which was obviously due to the cable mixup. The carbs 100% need to be synced, I can tell just by hearing it. So that is going to be my next thing.

    Thank you guys for the incredible help. I’ll keep the thread updated on the sync etc
     
    k-moe and hogfiddles like this.
  19. Xjnick

    Xjnick Member

    Messages:
    30
    Likes Received:
    4
    Trophy Points:
    8
    Location:
    Arizona
    Bike now starts without any starter, idles fine. Only now, when I give it some gas, one or two of the carbs seems to make a “puff puff puff” type of noise before it starts making a decent revving noise. And then when I put it in to gear and try to go, it sorta just puffs out and dies. Any thoughts?
     
  20. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

    Messages:
    14,626
    Likes Received:
    5,008
    Trophy Points:
    113
    Location:
    near utica, new york
    -Verify that you are getting spark on all 4 plugs
    - have you running-synced the bike yet
     
    Eddieo123 likes this.

Share This Page