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many questions about vacuum.... (petcock and carb sync.)

Discussion in 'XJ Technical Chat' started by kellenholgate, Sep 8, 2007.

  1. kellenholgate

    kellenholgate Member

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    First - petcock vacuum. I checked my oil today and the level had...risen. Odd, but from this forum i figured the only possibility was gas in crankcase. I opened the filler cap and gave a sniff. Sure enough... Smelled gasoline. So I drained the oil. While it was draining i pulled the gas line to verify my diagnosis of weirdness in petcock.

    Uhh.... it worked fine. on prime it drained freely. On or Res, nothing. I pulled the vac line off of the manifold, and gave it a suck. Gas flowed. It didn't take much vacuum, but plenty that it was definitely closed when none was present. So....what could cause leak down if the petcock is functioning properly? My only guess is that I left it on prime at some point accidently...which is doubtful. I'm kinda stumped.

    Second question, and this one hit me a couple minutes ago. I bought vacuum gauges at Harbor Freight to sync the carbs. After I refilled the oil today, i pulled the tank and went away. What I couldn't get from my Clymer manual was this......

    are the adjustment screws for a particular carb, or do they equalize between carbs? With three, I figured that they equalized betwen the carbs that they were between, but then I remember that #3 isn't adjustable. I adusted the screws until they were pretty even on the gauges, but if the setting is for individual carbs, I can probably go back and make it more accurate. BTW i made one of ricks homade restrictors, and the needles were still dancing like CRAZY. They evened out at higher revs, but I don't know if this throws off the measurements. Either way, what I did do helped my idle immensly, but I can tell that there is still some tuning to be done.

    Sorry this was a novela.... thanks for dealing with all of my stupid questions...constantly.

    thx in advance for any help

    kellen
     
  2. MiCarl

    MiCarl Active Member

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    Petcock:

    You mention functioning properly on PRI and RES, but no mention of ON. Have you checked the ON position? My petcock worked fine on RES, flowed on PRI and also flowed when ON without vacuum.

    Sync:

    The sync screws adjust the relationships between pairs of carbs, hence 3 screws. The #3 carb butterfly is held open (at idle) by the idle stop screw, unless you bottom out one of the other butterflies the sync screws won't affect the opening on #3 - and then only to open it.

    So, #3 being considered fixed the others are brought in line with it. The screw between #3 & #4 is used to bring #4 in line with #3. Then the screw between #1 and #2 is used to match that pair. Finally, the screw between #2 and #3 is used to pull the 1&2 pair in line with #3.

    Of course as you do this RPM will change - changing the readings and necessitating an idle speed adjustment. Then you tweak it in some more.

    If you bottom out a butterfly you will get weird results. The more you turn the screw that direction the faster the idle (because you are lifting the other 3 butterflies). You'll get real excited thinking you are really nailing it, but the idle screw has no effect and you have a 3K idle. Time to turn that last sync screw the other direction.

    Of course if your valve clearances are out of spec. you are wasting your time.
     
  3. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    Also, you really do need to block off the YICS chamber in the cylinder head with the blanking tool before synching the carbs.

    As well as adjusting the valves (before synching) as MiCarl points out....
     
  4. kellenholgate

    kellenholgate Member

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    Yics was blocked off. Fuel does not flow on ON... sorry i didn't mention that. I have not checked the valves, and I probably won't until this winter. I'm concerned with keeping this (my first) bike rideable until it starts to snow, then I'm going to do a top to bottom restoration this winter. If the adjustment screws are dealing with the relationship between carbs, then I did it right. My idle is much more even now, so that would make sense, i was just wondering if there was an easier way to get there. either way, to get it pretty even across the carbs only took about 20 minutes with me shutting the bike off to cool and to move gauges around (I only have two.) Thanks for the help...

    still need answer about gas in oil. i'm trying to wrap my head around this. even if the petcock was leaking.... a float would have had to go down...then not float back up, so the carb bowl keeps filling. right? so does the bowl have to overflow to make its way into the cylinder? Otherwise why doesn't the full bowl just flow into the cylinder after anyone shuts off bike?

    thx for the help so far, and any in the future
     
  5. Polock

    Polock Well-Known Member

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    try rolling a 1/2 inch piece of paper towel up real tight and jam it in the vacuum line, rip off what you can't get in then push it in with the gauge
    that should get the flutter down to about one number
     
  6. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    The float needle may be stuck open, although you would have many more problems than what you describe if that were the case. Maybe it just sticks open some of the time.........
     
  7. Polock

    Polock Well-Known Member

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    could you tell how much gas was in the crankcase ?
    doesn't take much to smell a lot
    this is pure theory
    if the petcock works as it should, consider the on the sidestand the right carb is higher than the left, if #1 float leaks it gets gas from 2 3 and 4
    try using the center stand and see what happens ?
    hay it sounds good
     
  8. MiCarl

    MiCarl Active Member

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    kellenholgate: You are correct that you have a float/needle/seat problem.

    Fuel both needs to get past fuel valve and needle/seat to leak into the engine. Assuming your fuel valve works correctly every time then you probably left it on PRI or as Polock said some fuel is running down from the high carbs when on the sidestand.

    New needles and seats are cheap. Put them on your winter project list. After I put new needles and seats in mine I accidentally left it on PRI overnite. Not a drop of gas in the oil.
     
  9. kellenholgate

    kellenholgate Member

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    sick... well i left it last night and it didn't leak, so i dunno if it was an intermittent problem.... there couldn't have been much gas in the oil though, because when I drained the tainted oil, there didn't seem to be any more than normal (i didn't actually measure it, but it seemed normal.) I just drove it to the store though, and as i got out, the #1 carb had overflowed.... before i rode home, i socked it a little with my hand to see if it would unstick, and upon arriving at home...nothing. Can you get to the floats without pulling the carbs off of the bike... i guess the 2 and 3 carbs would be harder, but if the 1 carb is the problem, can I recondition just by pulling the tank?

    thanks for the help so far....and i'll try that vacuum trick... that will probably get me a more accurate sync.

    thanks

    kellen
     
  10. MiCarl

    MiCarl Active Member

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    One day you'll be able to yank the rack of carbs off and put them back on blindfolded. Might as well start your training now. :wink:

    I had one doing the same thing. I went ahead and replaced all 4 while I had the rack off.
     
  11. RickCoMatic

    RickCoMatic Well-Known Member

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  12. Hired_Goon

    Hired_Goon Member

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    Yor symptoms, while intermittent would point me towards some crap or rust flaking off in the tank.

    Eg, if you shut the bike down and a bit of muck gets stuck betwwen the o-ring in the petcock then it will leak. Also, if one carb floods intermittently then that can be crud in the float valves.

    Have you flushed the tank out recently? Got an inline filter?
     
  13. kellenholgate

    kellenholgate Member

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    yeah rick, i made those restrictors... maybe i used the wrong kind of fuel filter (i used the smallest lawnmover filter..) but it didn't work too well. I had to kink the lines with my hands the tame them down, but it was a tad counter-intuitive and i started running out of hands... Either way, i got the job done and its pretty accurate. I'll probably pull the carbs off i guess this weekend, so I'll be able to correctly bench sync and do it again.... thanks for the help.

    oh yeah, i have a fuel filter, and i have a new one to replace it with the next time the tank comes up.

    thanks again for the help.

    kellen
     
  14. Maximator

    Maximator Member

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    As far as your petcock goes, I went through the same issue last week. I had the tank off numerous times with the vacuum operated ports showing no signs of leaking whatsoever.

    I found the gas getting into the oil but couldn't understand how so much could get through the float valve if the petcock wasn't leaking. While changing between prime and on positsions with no fuel line I happened to find that there were a couple of positions that it would leak in if not pointed directly at the ON position.

    After experimenting with it in the prime position I discovered it does not leak, so that is where I leave it. Now even though my number 3 carb is still leaking through the float valve, it's not enough to cause trouble with the oil.

    I'll just make sure to fill the tank before there is any risk of running out. When my riding season is over I'll rebuild the petcock and do a major cleaning/overhauling of the carbs.
     
  15. kellenholgate

    kellenholgate Member

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    I put the bike up on the centerstand, and the #1 carb isn't overflowing anymore.... so i wonder if if just leaked the excess from the 2,3, and 4 float bowls into the 1 carb, which has a sticky float.... and into the case. I'm gonna pull the tank again this weekend and see, but either way, I'm gonna get an inline fuel valve until i can rip into this winter. I don't really want to have to change the oil every time something goes screwy with my iffy petcock... we'll see. Either way, i'm gonna try to do carb clean this weekend too and see if i can do something about the sticky float.

    cheers
    kellen
     
  16. RickCoMatic

    RickCoMatic Well-Known Member

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    Take a sheet of 1000 or 1200 Finishing Paper and roll it up to fit the inside diameter of the Float Valve.

    Twist it to put a smooth shining finish on the Inside Diameters of the Valve Body's.

    That always works for me.
     

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