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VERY WEIRD start up problem

Discussion in 'XJ Technical Chat' started by cbcanada, Jun 23, 2012.

  1. cbcanada

    cbcanada Member

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    first let me say i am a newbie in wrenching bikes. having said that here is my story

    1981 xj750

    bike was running, and i decided to clean the carbs

    i sprayed seafoam diect into fuel line until bike would run no more

    i put fresh tank of gas and tried to start wouldnt start. looked at plugs they were soaked with seafoam and fouled

    i changed the plugs from bp7es to bpr7es (ic ouldnt find bp7es) and i snipped 1/8" off the plug wires because the contacts were bad and rescrewed them and confirmed spark in all 4 plugs

    i went to start the bike and noticed gas pissing out from my air box over flow hose.

    took the carbs back out and saw that i set the floats upside down, so i turned them over, put the carbs back on.. no more gas pissing from air box hose, i was happy !

    try and start the bike, nothing,,, i pull the plugs and all are dry and look brand new, there is no gas getting to the cylinder? there is no sign of combustion

    unfortunately i cannot use the drain screw to see if there is gas in the bowls because they are stripped. i did pull the gas line off the petcock and confirmed gas comes out at prime setting.

    so what do you think has happened here guys? i dont mind pulling th carbs again but before i do this i would like to know what could have gone wrong here so i know what to look for.
     
  2. MercuryMan

    MercuryMan Active Member

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    You did change the gas contaminated oil right?

    When you cleaned the carbs did you do more than spray seafoam? Did you check all your passages and jets to make sure they were free and clean? Clunk test the diaphragms?

    Most of what we do to these bikes to keep them happy is pretty easy, but the carbs are very particular and they won't be happy unless you go all the way and do it right. If not you will be just doing it over and over. Check out the articles here about how to clean properly if you haven't already. Search for "Church of Clean".

    You won't necessarily see any residue on your plugs if it's not firing whether or not fuel is going in. Without combustion they will still look brand new. I'm betting your float levels are off or your pilot circuit is clogged/dirty.
     
  3. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    You will need to get at least one drain screw free; then you can "walk" that float bowl down the rack and use it to "WET" SET YOUR FLOAT LEVELS.

    The float levels in these carbs are critical, and the spec is within a couple millimeters ( +/- 1mm each way) so you can't just throw them back on and expect them to work properly. http://www.xj4ever.com/setting%20fuel%20levels.pdf

    Read this: http://xjbikes.com/Forums/viewtopic/t=14692.html and this: http://xjbikes.com/Forums/viewtopic/t=2908.html

    And maybe, just maybe, you won't have to keep taking them back on and off.

    Oh, and you'll need to have your valves in spec in order to do the final vacuum sync: http://xjbikes.com/Forums/viewtopic/t=14827.html
     
  4. KrS14

    KrS14 Active Member

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  5. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    More like a continuing saga...
     
  6. cbcanada

    cbcanada Member

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  7. cbcanada

    cbcanada Member

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    not yet changed the oil . wanted to see if it starts first.
    to clean the carbs i removed all jets an soaked then in seafoam over night.
    i couldnt remove one jet because the top was stripped.
    i also cleaned the carbs in hot water and the sprayed the exterior moving parts with wd40.

    i did vissualy make sure jets were clean.

    i believe i set something wrong. because after my cleaning the first time i put the carbs back on they were over flowing. so i took them off and flippped the floats and now no gas is getting there.
     
  8. ryancdossey

    ryancdossey Member

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    Saw this on your other thread on the same topic.


    By the way.. You can. Download the photo bucket app. You do have to make an account it is free and takes less than 5 minutes. It will give you an image code to post. You'll simply copy that and paste it into your threads. ;) that's how I do all of my pictures on here.
     
  9. cbcanada

    cbcanada Member

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    okay recleaned carbs and put back together and she is running!
    now going to do the oil change. i ordered the clymer for it but still not here. where is the oil drain plug? 1981 xj750
    i dont see it underneath
     
  10. cbcanada

    cbcanada Member

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    i have 4 in 1 headers. is it hidden above it and i have to remove the headers?
     
  11. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    Not with most systems, but...

    Anyway, here 'tis, it's on the front of the sump (oil pan:)

    [​IMG]
     
  12. RickCoMatic

    RickCoMatic Well-Known Member

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    The SeaFoam might have loosened-up some matter that won't pass through a Jet.

    It dissolves matter surrounding Metering Ports and Orifices and cloggs the Orifice or Passage.

    You are probably going to have to Strip the Carbs and do a 1st Rate Job of Cleaning ALL the Individual Components.


    AFTER SEAFOAM TREATMENT TO CARBS THAT NEEDED CLEANING:

    [​IMG]
     
  13. cbcanada

    cbcanada Member

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    thank you so much. i believe the bolt is accesible without removing the headers. i have packed it in for the night. glad to have got the bike running with all your help. i ran it for only 3-5 min. because i figured there was gas in the oil from when the carbs over flowed.

    while it did run for 3-4 minutes i noticrd some burning smoke coming from the right side. about 3 inches below the cylinder head. it looks as if its coming out of the heat grills. makes no sense but i will look further into it after the oil change

    the saga continues! :)
     
  14. cbcanada

    cbcanada Member

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    ok is that round thing with the heat grills where the filter goes?

    so i am draining and then changing the filter and filling back up from the brake side where the oil cap is...

    no special instructions in the oil chainge?
     
  15. Ground-Hugger

    Ground-Hugger Member

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    When doing oil change make sure the bike is on the center stand. If it is not you will not be able to put the proper amount of oil in the engine. with bike on center stand fill oil until just a bubble of air appears at the top of the sight glass. There is a fill line there but it is hard to see sometimes.
     
  16. ryancdossey

    ryancdossey Member

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    Question on this.. Anyway to get around that? my bike was laid down and I had to remove the center stand... Can I get like the type of stand they use on newer sport bikes to do the same thing?
     
  17. cbcanada

    cbcanada Member

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    i dont have center stand either. i will have some one sit on the bike and hold it straight
     
  18. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    You need to know about checking on the centerstand as above; and not overfilling to begin with. There is a little number (2300CM3 or similar) cast into the clutch cover right by the oil filler cap. That is your oil level in CC's (CM3=CC.) It's OK to overfill by a couple hundred CC's, so that the level is all the way up in the window but with a bubble still showing at the top.

    When checking the oil, not only does the bike need to be held vertical, it needs to have been OFF for at least ten minutes beforehand.

    Oh, and don't overtorque the filter bolt. It only needs something like 11 ft/lb.
     
  19. cbcanada

    cbcanada Member

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    ok i drained the oil and took off that round grill that sits above the drain screw(you can see in the pic above)it came off as whole piece... i am assuming the filter is in there but its inclosed how do i get to the filter
     
  20. cbcanada

    cbcanada Member

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    got the filter out... okay putting the new filter on. is the curved in side of the filer face the bike or outwards?
     

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