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Carburetor Issues on my 1982 xj650

Discussion in 'XJ Technical Chat' started by midnightmaximguy, Jun 3, 2014.

  1. midnightmaximguy

    midnightmaximguy New Member

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    I am having some serious issues with my 1982 Yamaha maxim xj650. I have taken apart and cleaned my carbs at least 5 times and my bike still wont run. It will idle fine for a little while but if you try to give it gas, it will hesitate. If you try to ride it, it wont run but a minute and It will completely die. I runs only on prime and choke. If you set it on prime, you don't need choke, and if you open the choke, you don't need prime. There are no vacuum leaks and as far as I can tell, my carbs are clean. The only thing I did was, on the bottom of my carbs, I stripped the heads of some of my jets. Not in the chamber where the needle goes, but the chamber with my floats.
    I didn't think it would matter if I did, but I didn't have a flat screwdriver big enough. Any help would be greatly appreciated.
     
  2. Stumplifter

    Stumplifter Well-Known Member

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    Did fines from the jet heads getting stripped get lodged in those itty-bitty jet holes?

    Get an old set of screw drivers and grind them to a perfect fit.
     
  3. tabaka45

    tabaka45 Well-Known Member

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    Running only on prime indicates to me a problem with the petcock and fuel delivery. I'd check that before going into the carbs again. Also, open the carb bowl screws and see if you free flow of fues. If you go into the carbs be sure the jets are not reversed and the pilot system is ok.
     
  4. midnightmaximguy

    midnightmaximguy New Member

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    I was thinking it might be fuel delivery too. My carbs are clean but I guess I need to replace those jets that I stripped. It says in my instruction manual that any scoring or marking of the jets can upset the fuel metering rate and cause it to choke out or die. I guess that mistakes on me. I was just wondering where I can locate some jet kits at. The ones I found on ebay were really expensive, id be better off buying a used set of old carbs and cannibalizing parts that way. Il post pictures tomorrow and show what I did exactly and see if that helps at all.
     
  5. Hotcakesman

    Hotcakesman Active Member

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  6. tskaz

    tskaz Active Member

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    Running on prime but not on or res indicates either no vacuum to the petcock, or a faulty petcock diaphragm. If the bike is still staving for fuel with the switch on prime, I would suspect a faulty petcock/valve blockage.

    It could also be a blocked fuel filter inside the tank.

    It could also be float height set slightly low. On "on" the switch "drips" fuel into the carbs, which wouldn't allow them to fill fast enough to keep up with demand. On "prime" fuel flows freely, allowing the bowls to fill faster.
     
  7. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    What exactly is your definition of "taken apart and cleaned the carbs"? Be SPECIFIC so we have a better sense of what was done, and what might have been missed......

    Dave
     
  8. midnightmaximguy

    midnightmaximguy New Member

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    I took and sprayed carb cleaner from the top down and flipped them over and sprayed them out that way too. I cleaned my pilot and air jets, top and bottom, and cleaned my diaphragm and that little space where the needle jet for my floats go too. Based on what I've gathered, its like a fuel delivery problem. I guess I'll get a new petcock and see where that leads me.
     
  9. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    So you did NOT completely disassemble them, pull the emulsion tubes out, take apart the enrichment circuit, replace throttle shaft seals, OR fuel supply O- rings-----

    Did you bench- sync them? Did you get it to run long enough to try to do a running-sync?

    Did you do a valve shim clearance check?

    Is the vacuum line hooked back up to the petcock? Is the vacuum line any good ?

    What was then condition of the bike when you got it?

    Still too many things unanswered......
     
  10. pillowmaster50

    pillowmaster50 Member

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    Check that the floats are not installed upside down. Check that the petcock works correctly. Check that the two jets under the diaphragms aren't installed backwards (at least one service manual is wrong with respect to the locations of the air jets).
     
  11. midnightmaximguy

    midnightmaximguy New Member

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    I put my carbs back in tonight and my bike will only run on prime, but it runs pretty damn good. No hesitation, steady idle and acceleration.
    I rode for a couple miles and had it up around 50 and it was acting a lot better. But when I put it on run, it will not take gas and die. The motorcycle was in rough shape when I got it. Never had an oil change, dead plugs, and the carbs were dirty. But after I took care of those it was alright for a little while. I didn't anything to get my carbs out of sync. It was running good after I cleaned my carbs the first time. I just decided to go back into them and that's where I lost it. But now im pretty sure its either the petcock or my fuel line that's in need of repair.
     
  12. SQLGuy

    SQLGuy Well-Known Member

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    Generally you can disassemble and clean the petcock with carb cleaner. There is a little hole (and a check valve, IIRC) for the vacuum to operate the diaphragm... make sure that's not clogged.

    Also make sure you're actually getting vacuum to the petcock when the bike is running.
     
  13. pillowmaster50

    pillowmaster50 Member

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    Yup. If bike runs fine on prime but not on on or reserve, there's a problem with the petcock! You should check that the petcock isn't working correctly by taking off the fuel line and the vacuum line at the manifold side, then suck on the vacuum line and gas should come out of the petcock. Try this with the valve set to both reserve and on. If gas doesn't pour out then there is an issue. Follow sqlguy's advise to clean the petcock innards; I would like to add that the vacuum diaphragm may have a hole in it and will require replacement... Or you can just replace the whole petcock - chacal/Len can fill you in on your options.
     

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