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.

Air mixture screw

Discussion in 'XJ Technical Chat' started by Plumper, Jun 21, 2019.

  1. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
  2. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    Is this the air mixture screw?
     
  3. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    It's a tiny flat head in that hole
     
  4. Franz

    Franz Well-Known Member

    Messages:
    4,271
    Likes Received:
    1,212
    Trophy Points:
    113
    Location:
    Scotland UK.
    Which bike do you have?
     
  5. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    82 xj 750 maxim
     
  6. XJ550H

    XJ550H Well-Known Member Premium Member

    Messages:
    13,199
    Likes Received:
    3,861
    Trophy Points:
    113
    Location:
    Great North Woods
    yes that's the mixture screw for the pilot jet circuit

    you want a screw driver that fits tight into the slot .just make sure your screw driver sides also fit into the hole. soak in penetrating oil
    kroil is the best penetrating oil . also called aero kroil comes in an orange can ​
     
    k-moe likes this.
  7. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    Perfect thanx, so that's the one I keep reading about that you seat gently then 2.5 turns out, the factory caps were off so they've been screwed with at some point,
     
  8. XJ550H

    XJ550H Well-Known Member Premium Member

    Messages:
    13,199
    Likes Received:
    3,861
    Trophy Points:
    113
    Location:
    Great North Woods
    caps off could also indicate someone knew how to clean carbs. when you get the set for the last time you can replug them with disc or get rubber plugs to keep the crud out
    you will end up closer to 2-3/4 to 3 turns out when done tuning
     
  9. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    How can you tell when it's set correctly and should they all be the same turns out like all 2.75 or all 3
     
  10. XJ550H

    XJ550H Well-Known Member Premium Member

    Messages:
    13,199
    Likes Received:
    3,861
    Trophy Points:
    113
    Location:
    Great North Woods
    by the plug color or get a color tune .
     
  11. k-moe

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

    Messages:
    19,647
    Likes Received:
    6,756
    Trophy Points:
    113
    Location:
    The City of Seven Hills
    If you have a good ear you can tell, but that takes a lot of practice, and results in a failry coarse setting (in the ballpark, but not "perfect").

    If you can read a sparkplug for color and heat you can tell. Less practice required, but a bit tedious and relatively slow (but cheap).

    If you can do neither then you should invest in a Gunson Colortune. It allows you to see the combustion as it occurs, and adjust the mixture until the burn is correct.

    The will not all be at exactly the same number of turns out (but they should be pretty close). The mixture needs to be adjusted in relation to how much vacuum each cylinder is pulling (affecting airflow volume to that cylinder). A very healthy engine will have all the idle mixture screws very close to one another. A very sick engine will result in the opposite.
     
    XJ550H likes this.
  12. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    i better go the colour tune way, is there a certain way to do the test or just start at one side and work your way over
     
  13. Colin 85 700

    Colin 85 700 Active Member

    Messages:
    487
    Likes Received:
    131
    Trophy Points:
    43
    Location:
    Thunder Bay, ON
    Most say start at 3 then 4 1 2, the readjust, as you adjust eack cylinder it affects RPM and therefore affects vaccuum on each cylinder, run thru 3 times till all are good to go
     
  14. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    Ok thanx, sounds easy enough, looking at the prices of these colortune things I'm probably gonna go with the look at the spark plug method, still gotta buy a front tire soon
     
    k-moe likes this.
  15. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    So would this be a good plan of action, spray the screws with penetrating oil turn the screws clockwise and gently seat with proper size flat blade, back them out to 2.5 turns and start with that, go for a ride and see what the spark plugs look like, then adjust screws if need be.
     
  16. k-moe

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

    Messages:
    19,647
    Likes Received:
    6,756
    Trophy Points:
    113
    Location:
    The City of Seven Hills
    A good plan would be to remove them and make sure the o-rings are in good shape, then soft-seat them and set the baseline. That will give you some clue as to how well, and how long ago, the PO cleaned the carbs.
     
    Chitwood likes this.
  17. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    Ok I'll ad that to my plan I've taken the carbs out a couple times so I'm getting quicker at it
     
  18. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    I bought new spark plugs and when I changed them I noticed the 2 on the clutch side had white ashy tips and the 2 on the brake side had black soot on them, so that's another reason I wanted to play with those screws
     
  19. XJ550H

    XJ550H Well-Known Member Premium Member

    Messages:
    13,199
    Likes Received:
    3,861
    Trophy Points:
    113
    Location:
    Great North Woods
    one side to the other
     
  20. XJ550H

    XJ550H Well-Known Member Premium Member

    Messages:
    13,199
    Likes Received:
    3,861
    Trophy Points:
    113
    Location:
    Great North Woods
    cylinders are numbered 1 2 3 4 from left to right as you sit on bike.

    which bike are we talking about?
     
  21. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    82 xj 750 maxim, so to correct my previous statement 1&2 are white and 3&4 were black,
     
  22. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    So went for a test run tonight, happy to say no leaks and new mufflers work great and didn't fall off haha, but I had the bike ideling good in the driveway then I left drove for about 10 mins pulled over and the bike stayed at about 3000 rpm when stopped so I turned the big idel knob down so I had a good idel again, I should mention when I say good idel I can also rev it and it will drop back down to normal, then I drove for about 10 more mins stopped and it stayed high again, am I adjusting it wrong? Seems like the I turn the idel up for warm up then I gotta turn it back down once it gets hot, o ya 82 750 maxim
     
  23. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    And I haven't adjusted the the air mixture screws yet I was gonna do that tomorrow and the carbs are only bench synced cause I haven't made the homemade tube gauge yet
     
  24. k-moe

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

    Messages:
    19,647
    Likes Received:
    6,756
    Trophy Points:
    113
    Location:
    The City of Seven Hills
    The engine will idle at a higher speed when it is fully hot than when it is just warm.

    You will want to adjust the idle mixture screws and perform a running synch to be sure that all cylinders are being fed equally, or your idle will never settle back down consistently.
     
    Chitwood likes this.
  25. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    Ok I'm gonna do the mixture screws tonight, so should I set the idel when the engine is fully hot?
     
  26. k-moe

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

    Messages:
    19,647
    Likes Received:
    6,756
    Trophy Points:
    113
    Location:
    The City of Seven Hills
    If you do the whole process at once the engine will be hot enough.
    You will be adjusting the idle speed as you perform the running synch. It may need to be adjusted again after your first ride.
     
  27. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    Gotcha ok thanx
     
  28. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    O ya I have a yics engine and I read there's holes to plug while you sync, where are these holes and what's the best way to block them while sync,
     
  29. Chitwood

    Chitwood Well-Known Member

    Messages:
    866
    Likes Received:
    375
    Trophy Points:
    63
    Location:
    Fort Atkinson, Wisconsin
    Dont bother. Not only do you run the risk of breaking the casting that the plugs thread into but in my experience there isnt a noticeable difference between being blocked off or not when syncing. Other opinions vary.
     
    cgutz, KrS14 and k-moe like this.
  30. k-moe

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

    Messages:
    19,647
    Likes Received:
    6,756
    Trophy Points:
    113
    Location:
    The City of Seven Hills
    If you can live with a synch that's only 99% perfect, then don't bother with blocking the ports.
    As a practcal matter you won't be able to tell the difference.
     
    Chitwood likes this.
  31. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    Sweet ok I can live with 99%
     
    k-moe likes this.
  32. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    So I watched a video by David Allen on carb sync, he had 2 baby bottles, do any of you know what fluid was in those bottles or what fluid I should use? And from what I gather carb 3 is home base, there's 3 adjust screws on the back of the carb are those for 1,2 and 4 carbs? if I'm on carb 2&3 would I just move the vacuum line from the gas tank to 1 or 4? What do I do if the fluid in the bottle gets sucked into the carb?
     
  33. k-moe

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

    Messages:
    19,647
    Likes Received:
    6,756
    Trophy Points:
    113
    Location:
    The City of Seven Hills
  34. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    The valve clearance is good I did those, all 8 were out big time, I had to drop 2 sizes on a few of them
     
    k-moe likes this.
  35. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    O ya forgot to mention I did my mixture screws they felt about 4- 4.5 turns out, I seated them and turned them all 2.5 out but then when I started the bike it seemed like it was really starving for gas or air I couldn't turn the big knob fast enough before it stalled so I turned em all so there 3 turns out seemed to help a bunch, I'll probably stop messing with it till I do that carb sync
     
  36. ColoradoDan

    ColoradoDan Active Member

    Messages:
    433
    Likes Received:
    75
    Trophy Points:
    28
    Location:
    Longmont, CO
    Have some patience, and be prepared to spend quality time with your bike. Setting the mixture screws is not a fast job.

    You want to do it right so you don't have to mess with it again for a long time.

    It's been a few years since I did my carb sync. I ride year-round and I am shocked everytime I rev her up and she still sounds like a tuned sewing machine.
     
  37. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    I defenetly wanna do it right, I've fixed and adjusted a lot of stuff so far and now I'm just down to this idel thing, I know for sure it's been at least 4 years since the last sync cause that's how long my buddy had it before he gave it to me, so who knows when it was done last,
     
  38. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    So I got a pretty good understanding of how to do a running sync I read a bunch of threads on here, but there's one thing I didn't see, is there a setting that the idel knob should start at? Like the 2.5 turns for the mixture screws, or just play with it till I got a steady idel then start the sync and adjust as I go. I couldn't find your write up k-moe but I did read one with pics of a carb and which way to turn screws
     
  39. k-moe

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

    Messages:
    19,647
    Likes Received:
    6,756
    Trophy Points:
    113
    Location:
    The City of Seven Hills
    The idle speed knob is what sets the #3 throttle plate during a bench synch. If you did that, then you will only need to adjust the idle speed knob a little as you do the running synch. If you did not do that, then you will just set it as close to the factory reccomended 1100 RPM as you can before performing the running synch.

    You may find (as many of us have) that your cold starts will improve if you bump the hot idle speed up to somewhere between 1200 and 1400 RPM.
     
  40. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    Ok thanx I'm gonna pick all the crap up I need to make a gauge and do it Saturday morning
     
  41. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    Well I would say today's carb sync was a big fat win, I did 1&2 first it was like watching someone drink a slurpee, I got those to sit still then I did 3&4 those weren't to bad little bit of movement not much, then I did 2&3, again big movement got those to sit still, went for a rip, had to pull over couple times and make adjustments because of high idel when I stopped, but I think I got it now, went through a few stop signs and my idel stayed pretty good, gonna go for another little spin tonight to see how it dose, fingers crossed
     
    k-moe likes this.
  42. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    This is my new sync tool, ugly as hell but it was $16 to make and worked like a charm IMG_8082.JPG
     
  43. MaximusXJ650

    MaximusXJ650 Member

    Messages:
    147
    Likes Received:
    19
    Trophy Points:
    18
    Location:
    West Yorkshire
    Got a how to on how to make this?
     
  44. k-moe

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

    Messages:
    19,647
    Likes Received:
    6,756
    Trophy Points:
    113
    Location:
    The City of Seven Hills
    Look at the photo above.
    Two bottles of equal size that can hold vacuum wthout collapsing.
    Vinyl tubing.
    Automatic Transmission fluid.
    Drill holes in the tops for the tubing. Tape them, or use RTV, to close them off to atmosphere.
    The one thing not shown is two short peices of smaller diameter tubing that go into the longer tubes in order to dampen the vacuum pulses.
     
  45. XJ550H

    XJ550H Well-Known Member Premium Member

    Messages:
    13,199
    Likes Received:
    3,861
    Trophy Points:
    113
    Location:
    Great North Woods
    links on page 2 of this post
     
  46. k-moe

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

    Messages:
    19,647
    Likes Received:
    6,756
    Trophy Points:
    113
    Location:
    The City of Seven Hills
    HeH...forgot I did that.
     
  47. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    So second run I let it warm up for about 5 mins with the choke about half on, it was ideling at about 1200, but then I'd turn choke off and it would go to 900ish chug for a few seconds and stall so turned choke half on again started and took off drove for a few mins went through couple stop signs idel fine hit the 80 zone drove for a few mins turned choke off while I was driving, pulled over idels at 900ish then die so I started it and messed with the idel knob for a bit got good idel, drove for a little then the next time I stopped it idel at 900 but this time it didn't die it just kept ideling which was weird, so I turned it up to about 1200, then the rest of the ride it was fine, stayed at 1200ish every time I stopped, dos that sound like an air problem? I set my idel mixture screws all at 3 so maybe try 4 turns out? Also my vacuum hose is on carb 3 is that normal? Would it work better on a different carb
     
  48. k-moe

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

    Messages:
    19,647
    Likes Received:
    6,756
    Trophy Points:
    113
    Location:
    The City of Seven Hills
    I think you have the idle set correctly now. You have to set it when the engine is fully hot.

    At this point you shold be able to start it with little to no choke when the tempeature is above 55ºF.
    Allow it to idle until the engine speed increases suddenly (mine jumps up to 2,o00 RPM after a few minutes), then gradually shut off the choke to lower idle speed as the engine warms up. You can ride away on partial choke, just remember to shut it off all the way once the engine is warm so you don't waste gas or carbon-foul the plugs.

    You do not need to move the idle mixture screws out more. You already have them a bit on the rich side, but that's OK for now.
    The vacuum line should be on #3, but will work correctly no matter which vacuum port it is hooked up to.
     
    raskal likes this.
  49. Plumper

    Plumper Member

    Messages:
    112
    Likes Received:
    11
    Trophy Points:
    18
    Location:
    Taber
    Ahh ok sweet that's awesome then, I always thought if you can't turn choke off right away there's something wrong, so I should be able to leave it alone now just ride with partial choke then shut it off after a few mins, hell yeah thanx dude
     
  50. k-moe

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

    Messages:
    19,647
    Likes Received:
    6,756
    Trophy Points:
    113
    Location:
    The City of Seven Hills
    When it's hot enough outside you can start it up from cold without any choke and ride away within a minute or two.
     

Share This Page