1. Some members were not receiving emails sent from XJbikes.com. For example: "Forgot your password?" function to reset your password would not send email to some members. I believe this has been resolved now. Please use "Contact Us" form (see page footer link) if you still have email issues. SnoSheriff

    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.

XJ750 E-II carb questions

Discussion in 'XJ Technical Chat' started by zemville, Aug 24, 2014.

  1. zemville

    zemville Member

    Messages:
    45
    Likes Received:
    0
    Trophy Points:
    6
    Location:
    Philippines
    I recently replaced the throttle shaft seals on the carbs of the 750. I got the seals from chacal.I assembled the rack back together with new fuel line orings(acquired locally here in Philippines). Did a bench synch using the tiny little holes in the carb body. Also did a wet-set of thr float levels. I installed it back to the bike and it fired up right away even without the airbox(problem with airboxboots). However, I really had trouble making the bike to idle. If raise the idle, it will creep up and will have trouble idling down. If I put it around 1100rpm, It will slowly die/stall. I just backdown the idle speed adjust screw and tried to run the bike. It runs pretty well on low and high rpms even without the airbox. I just can't get it to idle but when I apply choke(fuel enrichment pluger), the bike idles pretty well. I removed the carb rack and inspected the butterfly plates. With the idle speed screw rod backed all the way out and putting a light behind the butterfly plates, I can see the light pass through. I can see the gap between the plate and the carb body. Do I need to adjust the plates so that no light will pass through? Or this is due to my air/fuel mixture screws adjustment? Or am I chasing another vacuum leak maybe from manifold?

    I assume the bike will idle without the airbox installed because my xj650j runs and idle even without the airbox connected before.

    Thanks guys!
     
  2. andrewc

    andrewc Member

    Messages:
    49
    Likes Received:
    0
    Trophy Points:
    6
    Location:
    guelph ontario canada
    It sounds to me like a sync problem.
    I'm not sure what the "little air holes" are.
    Do a sync with the vacuum stems from the carb to engine boots.
    After I rebuild carbs I put a halogen light behind them and like you said close the butterfly until it just shut the light down.
    Do carbs 1 and 2 then do 3 and 4 then bring 1 and 2 together with 3 and 4 using the screw adjustment between them.
    I find when I put them back on the bike and do a sync they are real close.
    Last time I did this I was out by one half inch of mercury on one carb. (not even enough to notice)
    You rev the motor up and the revs hang high. I would think this would have to do with the pilot jets. Screw them all the way in and then back out 2 - 2.5 turns for a start.
    Also if you haven't yet checked, check the o-rings and pilot needles to make sure they are not leaking by.
     
  3. zemville

    zemville Member

    Messages:
    45
    Likes Received:
    0
    Trophy Points:
    6
    Location:
    Philippines
    ^thanks for the input above.

    Im pretty sure that im out of synch because I havent use a synchronizer which I dont also have. As what I've read before, getting a good bench synch will be enough to get the bike to idle so I can do a vacuum synch.

    I think im gonna try to set the butterflies tomorrow. Could the gaps could realy be the culprit?
     
  4. andrewc

    andrewc Member

    Messages:
    49
    Likes Received:
    0
    Trophy Points:
    6
    Location:
    guelph ontario canada
    When I set the butterflys there is no gap.
    If you can't get rid of the gap completely then try loosening the two screws that hold the butterfly plate to the bar. It may with the spring pressure center itself better in the bore and close more completely.
    I really would make sure the pilot air circuit is clean also and adjust the screw to 2 - 2.5 turns for a start position.
    You said it runs better on the choke so I would think there is something up with the pilots.
    Use the straw in a can of cleaner to shoot through the ports. It should squirt out from a hole somewhere in the carb. If not then it's probably dirty.
    You need to get synchronizers to do a perfect tuning.
    I'm lucky enough to have access to a nice set so I don't have to buy some.
     
  5. zemville

    zemville Member

    Messages:
    45
    Likes Received:
    0
    Trophy Points:
    6
    Location:
    Philippines
    Thanks!

    I'll pull the rack tomorrow. I'll try to set the butterfly plates. Back all the way out for the idle speed rod. How about the synch screws? Do I need to back it out also so the plates would close totaly? I'll also inspect the pilot ports.
     
  6. Stumplifter

    Stumplifter Well-Known Member

    Messages:
    2,792
    Likes Received:
    1,051
    Trophy Points:
    113
    Location:
    near Irma, WI
    Here is a great, detailed article from Gamuru on how to bench synch.
    http://xjbikes.com/Forums/viewtopic/t=6366.html

    You can also use business card stock instead of paper clips. Cut the stock into 1/4" wide strips and it will contour to the radius of the bottom of the butter fly valve.
     
  7. andrewc

    andrewc Member

    Messages:
    49
    Likes Received:
    0
    Trophy Points:
    6
    Location:
    guelph ontario canada
    I would back the idle speed rod off.
    The synch screws are what you use to adjust the butterfly opening and closing.
    Adjust them in the order I said.
    Synchronize carbs 1 and 2 together (so that the light just stops showing through both together equally) by turning the synchronizing screw located between those carbs.
    then do the same to 3 and 4.
    Then synchronize carbs 1 - 2 and 3 -4 together with the synchronizing screw located between both sets in the middle of the rack.
    When you are done then adjust the idle speed screw in until it just makes contact. Then once you start it up you can speed it up from there.
     

Share This Page