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  1. #1

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    Default xs650 flooding... praying to the carb gods

    I've come crawling back again for some advice... I know there are plenty of threads about the float valves and flooding issues with the xs650, but I can't crack this one, hoping you'll bear with me..

    So, I should've been all set to put a cap on my first ever build yesterday, got the tank mounted and the petcock hooked in, and for the first time since May, the bike had everything it needs to run. I turned on the lights, opened up the petcock, and got ready to kick my heart out, when gas started to leak heavy out of my shift side air filter.

    Now, my petcock situation is nothing remotely close to the stock situation. I have an old Sportster tank with a manual petcock that splits down the line to feed into the T that feeds both the carbs, and the line that feeds in ahead of the shift side carb. My immediate thought was that the line that doesn't feed directly into the carbs must be some kind of reserve that only works with the stock petcock, and was causing the flooding. (I realize Im probably completely wrong, but I thought I'd try the most obvious thing first) So, I just connected my petcock to the fuel line that T's directly into both carbs, kicked it a bunch to no avail, and proceded
    to watch gas leak from now both air filters. I thought it was just flooding from too many kicks, but it responded directly with the petcock valve. petcock valve open: gas leaking from both filters, closed: nothing. it is worth mentioning here that there are no leaks in the line either, just the carbs.

    So, research suggests this probably has something to do with the floats. I was hesitant to believe this, as the PO (someone I trust) had the carbs completely gone through a week before I bought it, and they ran great back in may. Anyways, I opened up the bowls and reassembled the floats. They're the 1980 bs34s with the brass floats, No sticking, push pins and needles seem fine, and the height is where it should be at 27mm on both. Put the carbs back in, and still leaking, and engine not starting. (this was still with the petcock only connected to the carb T feed, not both lines)

    So, my question is could there be something else going on in the carburetors that's letting too much fuel in? Could it be my petcock situation? Do I need to connect my petcock to both of those feeds, or is one just a redundancy in the stock system?

    If you read this far, thank you. hope I was clear enough. I'll post some pictures when I get home in a couple hours.

  2. #2
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    I leak check carbs off the motorcycle so I can observe and fondle them. That includes removing float bowls with a fuel tank connected (outdoors) and observing when/if the needle tip/seat interface seals. Do that. I use a dummy tank but a longer fuel hose off your stock tank will do.

    Your fuel feed isn't the problem. Only overfill can cause flooding and in a gravity system fill is controlled by float/needle/seat.
    Last edited by farmall; 10-08-2019 at 9:21 PM.

  3. #3
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    Sounds like that is not uncommon and apparently the manual didn't update the float height specs when floats changed. Sounds like you got the right spec at 27mm for the brass floats - are you measuring with the gasket removed? Pay close attention to the float needle and seat area - any debris or damage? Floats are not flooded with fuel?
    The BS34 seat is push-in type, sealed and secured by an O-ring...o-ring good?
    Not XS650 float needles, but just an image of what to look for if needles are viton tipped:
    Click image for larger version. 

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    Could even confirm they are shutting flow off by blowing through a hose connected to the carb fuel inlet while carb is upright with float bowl removed, then raising the floats.

    Thread: Carbs are flooding like a faucet

    "...success just measuring with a 6" steel rule (graduated in MM on one side of course) but maybe I'm just more familiar with the process than most.
    There are some "gotchas" when dealing with the BS34 floats.
    The first year of these carbs, 1980, had normal brass floats just like the earlier BS38s. However, due to the different shape and size of the float bowl, the setting spec was very different from the earlier BS38 specs (by like 2 to 3mm).
    And to confuse matters even more, when the plastic floats came along in 1981, their setting spec changed again and doesn't match any of the brass float ones. To make matters worse, Yamaha didn't change the spec in the manuals, still listing the '80 brass float spec for later plastic float equipped models..."

    "So, here's the info you need to sort this mess.
    The 1980 brass float spec was 27.3mm .5mm.
    It's pretty common knowledge to measure the brass floats to the top edge of each round float "bulb".
    All the earlier BS38 carbs were in the 24 to 25mm range.
    The plastic float spec is 22 1mm. The plastic floats have an odder shape with a flat area up near the hinge so some confusion often arises as to where they get measured to. They are the same as the brass ones, measured to the top of the float "bulbs", like so ....."

    Click image for larger version. 

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    See more here:
    http://www.xs650.com/threads/carbs-a...-faucet.33591/

    http://www.xs650direct.com/products-35.html

    Sure the carbs ya got are the ones you think you got...
    Click image for larger version. 

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    and

    37 pages of great info here:

    The XS650 Garage Carburetor Guide

    http://www.amckayltd.com/carbguide.pdf
    Last edited by TriNortchopz; 10-08-2019 at 11:23 PM. Reason: carb pics

  4. #4

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    I agree with farmall 100%.

    Also, it was never mentioned whether or not the old brass floats were leak free... if they have a pinhole leak they'll take on fuel and negate static float height measurements.
    Last edited by Skjoll; 10-09-2019 at 5:38 AM.

  5. #5

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    thanks for all your help, and sorry for being inactive, been waiting for my package from mikesxs to ship. realized my needles were a little worn after seeing that picture, so i went ahead and replaced them and the valves tonight. still a leak on the shift side carb. gonna order new floats to see if that does the trick.

  6. #6

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    mail came today, got the floats replaced with a brand new set. Was VERY careful about setting them to the right height (27mm), and making sure everything is where it's supposed to be, facing the right direction, etc. in the bowls (nice video on that here: https://www.youtube.com/watch?v=YuhyMXxgI1Q&t=1243s). New needles and valves, AND new floats... the shift side carb still just pisses fuel.

    Any ideas? Could the intake be damaged causing a leak even before fuel reaches the bowl? Could the jets be clogged in a way that redirects fuel back towards the air filters? A problem with the diaphragms? The only other thing I can think of is that the bike sits on its stand at a pretty harsh angle, could it be so steep that gravity keeps the float from shutting the valve, or causes fuel from the higher carb to fall to the lower carb?

  7. #7
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    Where exactly on the carb does the fuel piss out? Regarding lean angle, does it stop pissin' if you stand the bike up straight?
    Did you try just blowing into the carb filler hose (yes, just stick your lips on it) with the bowl off while manually raising the float to confirm float valve is closing on the seat? With the float needle on the seat, you should not be able to blow through the fuel supply hose. If you can, you can trace the problem with air instead of fuel.

    I just took a look at that video; with carbs upside down like that on the bench and floats holding the float needles against the seats, you should not be able to blow through that fuel supply hose.
    Last edited by TriNortchopz; 4 Weeks Ago at 9:27 PM. Reason: video

  8. #8

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    just leaking out of the shift side air filter. still takes a piss when standing upright.

    went ahead and took the carbs off again, inverted them and blew through the hose and about had an aneurism.. seems to be a good seal..

    what in sam hell...

    I'll take the bowls off again and post some pics. maybe the floats are a bit too high?

  9. #9
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    Do you have a filter?????????? Is there trash in your tank????

  10. #10

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    I have an inline filter and I just cleaned my tank with a couple vinegar soaks and then lined it with kreem last week. It's good now, but the way I realized I had to do that in the first place was from seeing the shitty rusty fuel leak out of the carb when this problem originated...

  11. #11

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    here are the floats heights of the carb in question:
    Click image for larger version. 

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    Click image for larger version. 

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    and here's that new needle and valve
    Click image for larger version. 

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    everything look ok?

  12. #12

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    alright put the carbs back together after blowing some carb cleaner through the jets and the inlets. ran a leak test with the carbs off the bike, below the tank with a line going straight from the petcock to the T-inlet. no leak.

    emptied the bowls to make sure fuel was getting IN, then immediately put the carbs back in the bike, stood it up straight, turned the fuel on, and it leaks!?

    I am confused.

    does it have to do with this second inlet in front of the carbs???

    Click image for larger version. 

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  13. #13

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    just had another thought... my Springer is 6"+, plus a couple inches from the 21" front wheel. Rear wheel and rake are stock, so it's also a pretty steep angle from front to back. anybody heard of this happening with taller bikes?

  14. #14
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    Quote Originally Posted by beer9000 View Post
    just had another thought... my Springer is 6"+, plus a couple inches from the 21" front wheel. Rear wheel and rake are stock, so it's also a pretty steep angle from front to back. anybody heard of this happening with taller bikes?
    That is very possible......... Try lowering the float levels...........

  15. #15

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    lowered them to 24mm then all the way to 22mm, still leaks... gonna try raising the height above 27mm? running out of ideas. Once I had that lightbulb I really thought that was it, would make sense as that's the only thing that changed while it sat that would effect the carbs other than deterioration from old gas.

  16. #16

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    29 mm on both sets of floats still leaked too. any other ideas?

  17. #17
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    Quote Originally Posted by beer9000 View Post
    29 mm on both sets of floats still leaked too. any other ideas?
    What I would do is take them off of the bike....... Hook the fuel line to them turn on the gas and tilt them and see if you can create the leak off of the bike........

  18. #18

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    ok, I'll try that tomorrow. Been at it all day, time to go cry in the corner and come back later without frustration fueled ham-fists... thanks for all your help today bud

  19. #19
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    Maybe it time to check float level by seeing the actual float level using the clear plastic hose method, this Amal has a dot to indicate level:

    Click image for larger version. 

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    Got a drain on the bottom of your float bowl? - do the same thing with a clear piece of hose...set 'em up, use 30mm float height to start (since they leaked at 29), and in you case, install them so you can see the actual float level with carbs on the bike;

    From the XS650 site:

    "I just could not get the float levels correct by measuring them according to the specs. Then I tried this technique where
    1. I took off the carbs
    2. Set them up so they are level just like they would be on the bike.
    3. take off one of the float bowl drain plugs
    4. put a clear plastic hose tightly into the drain plug hole (size 5/16 fits very tight but it can be threaded on with force.)
    5. run the clear plastic hose down a coupe of inches to avoid a pinched line then looped it up so the end was higher than the top of the carb.
    6. Create a temporary fuel supply to feed the fuel intake line. I put a small funnel tightly on the end of the gas intake line. Then I poured fuel into the funnel slowly until the floats reached the top and stopped the incoming flow of fuel.
    If the floats do not shut off the fuel then gas will start coming out of the back of the carbs. Obviously your adjustments are off if that happens. Remember, lower float levels ( for example 22 mm in comparison to 24 means your floats are allowing more gas in at 22, not less. So 24 is leaner, 22 is richer)
    7. Pour gas into the funnel and keep pouring until the fuel in the clear tube will not go any higher. Then you know your floats are shutting off the fuel to the carbs.
    8. The fuel level in the clear plastic tube shows how high the fuel level is in the float bowl. From there I can tell which way I need to adjust the floats, up or down.
    9. It still is kinda messy as the gas has to be emptied out of the carb each time an adjustment is made, and there usually are several adjustments for each carb.(but you got a drain hose on the bottom of the carb).
    When the fuel level in the clear plastic tubing is even with the bottom of the float bowl flange (where it joins with the top of the carb) you are in the ballpark. That is where I stopped and my bike runs perfectly.
    You could try doing this while the carbs are on the bike but I wouldn't want to. Much easier to adjust if the carbs are off and easily accessible.
    If the tube is leaking, a little leakage is ok ( a drip now and then) a stream is not ok. Get a different size tube.
    Some folks buy an extra set of float drain plugs, drill holes in them and put on a nipple to make a very tight fit. I did not have the time to order, so I just used the 5/16 tubing and forcefully screwed it in. It worked fine. .."

    http://www.xs650.com/threads/carbure...leaners.20365/

  20. #20
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    ^^^^^^ Now that's one hell of an idea.............^^^^^^^^^^^^^^

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