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1974 tx650a Hesitation Issue

Discussion in 'The Garage' started by cmarts, Jul 8, 2018.

  1. cmarts

    cmarts XS650 Enthusiast

    I have a 74 and in any gear when I get above 3000-3500rpm the motor sputters and hesitates. Continues to try to pull up through rpm but just sputters. It worked perfectly for months until a few days ago so its not a jet sizing or needle problem.

    1. I recently wired a new brake light and plugged in a LED flasher unit. I couldn't get the turn signals to work so I just left it the way it is.
    2. Carbs, tank, fuel filters are all super clean. Tank is lined. Running premium only.
    3. Pulled plugs and noticed they were pretty sooty. Running rich. Cleaned and reinstalled.
    4. Bike has new condensors

    Can still get up to highway speed. Just sputters over 3000-3500.
     
    gggGary likes this.
  2. azman857

    azman857 '80 XS 650SG Rider Top Contributor

    Take the last thing you did before this happened off and see if it corrects itself. I'm betting on a clogged pilot jet myself.
     
    gggGary likes this.
  3. cmarts

    cmarts XS650 Enthusiast

    took apart carbs. Pilot, main jets and bowl were all clean. Passage ways all open
    Took brake light off. Didnt change anything.
     
    gggGary likes this.
  4. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    I had a similar scenario. The ancient harness connectors for the points and condensers developed a loose grip on the bullets, engine vibrations would create intermittent connectivity...
     
    gggGary and robinc like this.
  5. gggGary

    gggGary Stop that! XS650.com Supporter Top Contributor

    Get a timing light on it, check advance action. Watch points in dark room excessive sparking at points? New condenser; was there a reason for that?
    New doesn't guarantee functioning correctly. Spark strong and blue?
     
    JRP01, TwoManyXS1Bs and robinc like this.
  6. cmarts

    cmarts XS650 Enthusiast

    Checked the wiring under the tank last night. The PO had replaced 1 condensor. I noticed one of the wires was fraying at the bullet connector crimp so I replaced with new bullet connector. The other wire from the same condensor was soldered pretty roughly and wrapped in electrical tape, replaced with new bullet connector.

    The other condensor was replaced because I had an old one and a new one installed on the bike when I got it. The PO lost interest in bike and didnt replace the other old condensor yet, so i did when I got the bike.


    Will check timing.

    .
     
    gggGary likes this.
  7. 5twins

    5twins XS650 Guru Top Contributor

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    There's only one condenser "pack" on these. It's 2 condensers mounted on one bracket, each of it's 2 wires coming from one of the condensers.

    [​IMG]

    It should be mounted to the back side of the upper left engine mount. Each black wire runs to a points set wire, actually to a double female bullet connector that a points wire plugs into as well. You can see them here, behind the red spark plug wire .....

    [​IMG]
     
  8. cmarts

    cmarts XS650 Enthusiast

    Sorry if I wasn’t clear enough describing my wiring, but yes that is exactly how I have mine wired. I took it out for a spin and the problem persists. I am now checking timing and valves.
     
  9. cmarts

    cmarts XS650 Enthusiast

    Could this fraying on the points wire cause a problem?
     

    Attached Files:

  10. 5twins

    5twins XS650 Guru Top Contributor

    18,873
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    Yes, it could possibly. You may have to fix that crimp, replace it or repair it if possible.
     
  11. cmarts

    cmarts XS650 Enthusiast

    Fixed wiring. Attempted to perform dead cylinder method. Left cylinder couldn’t keep bike running unless I gave lots of throttle. It hesitated. My guess is the brand new coil is bad, thanks mike. I did notice that the left coil was quite warm after idling for a couple minutes while the right one remained cool.

    Is there an easy way to tell if a coil is toast? I think I will install old coil and see what happens.
     
  12. cmarts

    cmarts XS650 Enthusiast

    Never mind, should have consulted with the factory manual before asking....will post results of coil testing
     
    robinc likes this.
  13. cmarts

    cmarts XS650 Enthusiast

    Left coondensor:
    4.5 ohms primary, 13.75k ohms secondary
    Right condenser:
    4.3 ohms primary, 13.3k ohms secondary
    Seems to be good.
     

    Attached Files:

  14. 5twins

    5twins XS650 Guru Top Contributor

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    Are your carbs in sync or at least close to it? On the '74 carbs, each one has it's own idle speed adjustment screw. It could just be that you have the left one set too low. On your dual cable carbs, sync is a 2 step process. First you sync the idle speeds and then you sync the cable freeplay so both butterfly plates begin to open at the same time.
     
  15. cmarts

    cmarts XS650 Enthusiast

    I have synced multiple times, they are close. Engine sounds good. Been talking to others with the same issues and they think it may be the advance unit.
     
  16. 5twins

    5twins XS650 Guru Top Contributor

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    Advance issues are usually more advance rod issues. It needs to be kept lubricated so it will turn easily and advance the timing correctly. There are bushings with grooves in them at each end of the cam. These support the advance rod and the grooves should be kept packed with grease. That will provide adequate lubrication for the advance rod for many years. Check and re-grease maybe every 5 years or so.

    [​IMG]

    [​IMG]
     
  17. cmarts

    cmarts XS650 Enthusiast

    i think this is the problem. Advance weights were not snapping into place, noticed dry metal rubbing sound coming from cam when it was rotated. will clean advance unit and repack bearing with grease. Is there a detailed manual for this? My factory manual doesnt mentioned this at all, just setting points.
     
    Last edited: Jul 17, 2018
  18. 5twins

    5twins XS650 Guru Top Contributor

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    No manual mentions it, even though it is something that needs doing from time to time. You could consider it required maintenance even though it doesn't need doing very often. I guess Yamaha didn't figure the bikes would be around this long, lol.
     
  19. cmarts

    cmarts XS650 Enthusiast

    So how exactly do I get access to these areas that require grease? I see theres a 10mm bolt on the advance rod and a large retaining nut. Points side I could probably figure out but after taking the weight and springs off the advance side im not sure what the next step is.
     
  20. gggGary

    gggGary Stop that! XS650.com Supporter Top Contributor

    You got it remove nut and washer from RH, push advance rod out through points end. watch for the tiny locating dowels. note alignment, it can be reinstalled 180 degrees off, oops.... Springs can get stretched/loose, cut and rebend one to shorten it, there's how too's around.
     
    cmarts likes this.

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