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.

carb float heights

Discussion in 'XJ Technical Chat' started by joejr2, May 13, 2020.

  1. joejr2

    joejr2 Active Member Premium Member

    Messages:
    713
    Likes Received:
    109
    Trophy Points:
    43
    Location:
    Santa Fe,NM
    I set my floats with a gauge at 17.5 mm. When I did the wet test the fuel levels all were about 5/16" to 3/8"
    low. What is the ratio for raising/dropping the floats in the bowls to the fuel levels on the outside for the wet
    test ? I'm working on an 82 xj650 maxim but since the carbs were used I'm not sure of the volume of the
    float bowls.When I rebuilt them I saw that the jets were consistant with 82 maxim specs and I assumed the recommended float height off the carb rims was accurate
     
  2. XJ550H

    XJ550H Well-Known Member Premium Member

    Messages:
    13,199
    Likes Received:
    3,854
    Trophy Points:
    113
    Location:
    Great North Woods
    http://www.xj4ever.com/setting fuel levels.pdf
    Setting float height is just a guesstimate the above link walks you through setting actual wet set of the fuel level. It will tell you how many millimeters below the carburetor joint the fuel should be. Get one of the carbs set correctly and then measure you float height and that should be a closer standard for the last three.
     
  3. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

    Messages:
    8,866
    Likes Received:
    1,780
    Trophy Points:
    113
    Location:
    The room where it happened
    And then always verify the true fuel level in the bowl using the clear-tube gauge procedure. The whole "float height" procedure is a very kinda-sorta convoluted method of getting "close" to the proper fuel levels based on a known good carb's setting. Yamaha stopped publishing any "float height" measurements in their later service manuals because it's such an undefined, "sketchy" method of trying to achieve the proper fuel levels. If you're setting fuel levels on about 10 carb sets a week, then the method probably has some merit and benefits, Otherwise, it's always been just easier (for me) to set each carb individually using the direct approach---- the clear-tube gauge measurement of the actual fuel level, which, you're going to be using one way or another as the final part of the process, "float height measuring/adjusting" or not.............
     
    XJ550H likes this.
  4. joejr2

    joejr2 Active Member Premium Member

    Messages:
    713
    Likes Received:
    109
    Trophy Points:
    43
    Location:
    Santa Fe,NM
    What I wanted to know was what the measurements of bending the float tabs relate to the fuel levels in the tube on the outside. So, if I was following a
    Recommendation of 17.5 mmm which resulted in the level in the tube being 3/8" low, what would be an educated guess for dropping/raising the float ?
    Like start lifting the tab up 3 or 4 mm etc. to raise the fuel level in the tube at the next set test ?
     
  5. Fuller56

    Fuller56 Well-Known Member

    Messages:
    760
    Likes Received:
    345
    Trophy Points:
    63
    Location:
    Cary, NC (winter) Harpursville, NY (summer)
    I don't think there is a set, known measurement to bend the tab to get a measured response from the float level. My experience is that you bend the tab a tiny bit and the fluid level changes sometimes a lot, sometimes a little. It is a tedious procedure unless you have LOTS of experience like a couple of the carb gurus here do. I spent most a day on 1 uncooperative carb for my Kawaski ZG1000 a couple of weeks ago. It is one of those touchy/feely things. Good Luck, be patient and relentless, it is worth it when right.
    John
     
  6. joejr2

    joejr2 Active Member Premium Member

    Messages:
    713
    Likes Received:
    109
    Trophy Points:
    43
    Location:
    Santa Fe,NM
    Yeah, thanks I'm going to try 4mm and do another wet test
     
  7. joejr2

    joejr2 Active Member Premium Member

    Messages:
    713
    Likes Received:
    109
    Trophy Points:
    43
    Location:
    Santa Fe,NM
    So I raised the floats 3mm as an experiment and with the following wet test the fuel levels were perfect
    3mm below the bottom flange.
     
    Rusty81 likes this.
  8. XJ550H

    XJ550H Well-Known Member Premium Member

    Messages:
    13,199
    Likes Received:
    3,854
    Trophy Points:
    113
    Location:
    Great North Woods
    so you went from 17.5 to 20.5 float height
     
  9. joejr2

    joejr2 Active Member Premium Member

    Messages:
    713
    Likes Received:
    109
    Trophy Points:
    43
    Location:
    Santa Fe,NM
    No, I raised the fuel level by prying up the tabs 3mmm from 17.5 mmm to around 14- 14.5mm
     
    Rusty81 and XJ550H like this.
  10. joejr2

    joejr2 Active Member Premium Member

    Messages:
    713
    Likes Received:
    109
    Trophy Points:
    43
    Location:
    Santa Fe,NM
    How did those extra "m"s sneak in ?
     
  11. XJ550H

    XJ550H Well-Known Member Premium Member

    Messages:
    13,199
    Likes Received:
    3,854
    Trophy Points:
    113
    Location:
    Great North Woods
    voice feture on tablet gets me all the time.

    in past posts about float valve needles, I have read they are longer than oem needles which would account for the change in float setting from Recomended height.
     
    Last edited: May 16, 2020
  12. joejr2

    joejr2 Active Member Premium Member

    Messages:
    713
    Likes Received:
    109
    Trophy Points:
    43
    Location:
    Santa Fe,NM
    Stock plunger needles are #110. I try to clean those up and use them over again if possible
     
  13. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

    Messages:
    8,866
    Likes Received:
    1,780
    Trophy Points:
    113
    Location:
    The room where it happened
    #110 is the main fuel jet size..................
     
  14. 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
  15. joejr2

    joejr2 Active Member Premium Member

    Messages:
    713
    Likes Received:
    109
    Trophy Points:
    43
    Location:
    Santa Fe,NM
    whatever I did It worked. I originally made a template out of an old gift card that I set with a metric caliper at 17.5mm
    when I did the wet test the fuel levels were about 3/8" low. So, I made another template that was set 3 mm lower at
    about 14.5 mm +- this one was also set with a metric caliper. This time the wet test was right on the mark. 3 mm
    below the carb flange. What is confusing is that in setting the floats the carbs are upside down. Bend the float tab
    up and the float drops raising the fuel level . If you bend it down you lift the float dropping the fuel level.
    As far as the slide plunger needle, that was stock, I was confusing there. The float needles were what they were.
    I got the original 17.5mm float height off of a you tube video .
     
  16. 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
    Yes, for the 650/750 carbs, 17.5mm is the INITIAL setting. It’s just a starting point, baseline, whatever you wanna call it , starting point.
     
  17. Polock

    Polock Well-Known Member

    Messages:
    9,751
    Likes Received:
    2,093
    Trophy Points:
    113
    Location:
    Beaver Falls, PA
    the original float needles with the springy thing on top? did they all seem to springy the same?
     
  18. joejr2

    joejr2 Active Member Premium Member

    Messages:
    713
    Likes Received:
    109
    Trophy Points:
    43
    Location:
    Santa Fe,NM
    I picked up an aftermarket set of float needles with steel tips. they fit deeper into the seats and
    don't have the wire loops that hang off the float tangs. that probably accounts for the difference
    between 17.5 mm and what I ended up with 14.5 mm +-
    It's funny though, I rebuilt a set of carbs from an 81 650 maxim not long ago using the same
    steel tip needle and seat combination and 17.5 mm worked out on the first wet test
     

Share This Page