1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

2nd gen SV650 throttle stuck open

Discussion in 'Tech' started by WIslowpoke, May 23, 2023.

  1. WIslowpoke

    WIslowpoke Well-Known Member

    Like the title says, the "throttle" on my -08 SV650 stuck wide open towards the end of a straight at last weekend's event. This was during the first lap of the third session of the day. I managed to come to a somewhat controlled stop, and shut off the engine. The handle would open and snap shut just fine, so the throttle cables weren't stuck of impinged, yet the engine would howl and bounce off the rev limiter. I moved the bike to the paddock under its own power between sessions, afraid I was going to burn the clutch while doing it. After letting the bike cool a minute I tried re-starting the bike with the same results - WOT. I came back to the bike after another 15 min and - lo and behold - it ran just fine.

    The bike doesn't have any gauges, that's how I bought it. The gauges were pretty crudely removed, leaving a tangle of wires under the tank. The only "work" done on the bike to track down issues was moving some of loose wires ending below the throttle body toward the back of the bike. Anyway, I decided to take my chances on a recurrence and ran the bike the rest of the day, four sessions, without incident.

    I haven't removed the airbox to take a peek inside. The airbox was off just last week for attaching fairing brackets to the mounting holes on the inside of the frame so I know there's no rat's nest-type crap in the throttle bodies. Will a rudimentary examination by a complete amateur reveal any issues? I guess it's we could have left behind a piece of lint from the towel that was covering the throttle body while the airbox was removed, but could that have caused the issue?

    I'd appreciate the hive's collective wisdom before I strike out on my own to track down the cause of the WOT. Or I guess I could ride more, worry less. :whoosh:
     
  2. SundaySocial

    SundaySocial Blue & Gold

    There are both 'open' and 'close' throttle cables, and my immediate reaction is the 'close' cable is not present, is broken, or installed incorrectly.

    Is there slack in the throttle cable when it hangs at "WOT" ? If no slack, does the throttle have "normal" throttle tension when it sticks "WOT" ?

    1) Remove the Tank, and airbox.
    2) With the engine/ignition OFF, actuate full throttle movement.
    3) Observe if there is anything around the injector bodies that could POSSIBLY cause linkage bind; throttle cables/wiring/hoses which could cause it to remain WOT .

    ! Figure this out before it hurts you, or someone else !

    https://www.ronayers.com/oemparts/a/suz/506b5754f8700235b8766ff0/handlebar-sv650s-sa

    https://www.ronayers.com/oemparts/a/suz/506b5710f8700235b8766f9a/throttle-body
     
  3. WIslowpoke

    WIslowpoke Well-Known Member

    Thanks, SS,

    Good points. The throttle did snap back just fine while the engine was screaming wide open, seemed like the cables were working fine. There was no slack in the throttle cable while hanging WOT, as far as I could tell.

    Tomorrow evening I'll remove the airbox (and disconnect the umpteen hoses and wires going to it) and verify function of all related parts to the best of my ability.

    I failed to mention in my first post that I did also install a K&N air filter in the airbox while doing the fairing bracket work. Probably immaterial to the issue at hand, but anyway...

    Thanks for taking the time to respond, I'll reply with any findings.
     
  4. PeaPod

    PeaPod Well-Known Member

    Not necessarily immaterial. You very well could have dropped a bolt that is now hanging something up. Check to be sure all your bits and pieces are there and you're not missing something.

    Related story, buddy of mine lost a bolt from his airbox and it got stuck in his throttle body holding it open on an R6.
     
  5. E Reed

    E Reed Well-Known Member

    My bet is on something is holding the butterflies open. I've seen an air filter get sucked into the throttle body opening before. Take the airbox off and verify that the butterflies are closing all the way. If that's not it, check the TPS on the side of the throttle bodies. The screw that holds it in place could have come loose.
     
    PeaPod likes this.
  6. JJJerry

    JJJerry Well-Known Member

    I've seen pea gravel from a previous rounds gravel trap excursion work it's way down into the linkage and stick a 2G WFO going into T1 at Grattan. Thought it was all clean - missed a pebble or two somewhere.
     
    PeaPod likes this.
  7. WIslowpoke

    WIslowpoke Well-Known Member

    Thanks again all for your responses. I did find some time to remove the airbox and take a good look around and in the throttle bodies. I found
    - both cables from the throttle handle in good shape, very little slack
    - nothing to obstruct the spring mechanism on the clutch side of the bike that is actuated by the cables from the throttle handle and which rotates the spindle that opens / closes the front throttle butterfly
    - nothing to obstruct the movement of the rod situated on the opposite of the front cylinder throttle body which moves back and forth to open the rear cylinder butterfly in unison with the front one
    - nothing to obstruct the rotation of the spring unit that rotates the spindle for the rear butterfly
    - no signs of any debris inside the throttle bodies that could have caused them to stick wide open.

    Having not found anything, I sprayed some MAF cleaner on all rotating parts, wiped off some dust on the outside of the throttle bodies, and buttoned up everything. While doing that, I made sure no wires or hoses could obstruct any moving part, and that the rubber boots around the throttle body openings are properly tightened.

    Seeing that all parts are mechanically actuated and the cables, spring mechanism thingies and rods that move these parts are working as planned really didn't provide any answers. Thinking back, while the engine was screaming WFO, the throttle handle would still snap back just fine without any corresponding change in RPM. I tried opening the throttle and letting go of the handle while holding in place the rod that controls the movement of the rear butterfly. The handle would not snap back or move at all, i.e. if the rod or the spring mechanism movement were obstructed, the throttle handle wouldn't have snapped back freely.

    Somehow the engine kept being fed gobs and air fuel, regardless of the position of the throttle handle that, I've now confirmed, appropriately controls the opening and closing of the butterflies. I just don't know how.
     
  8. WIslowpoke

    WIslowpoke Well-Known Member

    Pics closed and open.
     

    Attached Files:

  9. Kurlon

    Kurlon Well-Known Member

    Check the boots for cracking?
     
  10. WIslowpoke

    WIslowpoke Well-Known Member

    Pretty cursory check, I'll go back and verify. Thanks.
     
  11. WIslowpoke

    WIslowpoke Well-Known Member

    I couldn't find any obvious signs of cracking or dryness on the boots.
     
  12. E Reed

    E Reed Well-Known Member

    As I mentioned before, did you check the TPS to see if it was loose? That's the throttle position sensor on the side of the throttle bodies. It is adjustable and if it is loose or was disturbed when you did the previous work, it will create the problems that you are describing. I can't remember off of the top of my head, but there may be an alignment mark on it from the factory. Look at a service manual and make sure it is aligned properly. I believe it involves jumping some wires on the dealer service plug and looking at some marks on the dash display.
     
    WIslowpoke likes this.
  13. WIslowpoke

    WIslowpoke Well-Known Member

    Thanks, Eric,
    I'll make sure the screws are tight. Adjusting it the TPS, if loose and out of whack, will be a whole different matter. I found a TPS adjustment thread (below) which provides a solution for jumping the dealer service plug and adjusting sensor position to provide better fueling at low RPMs. However, this requires using the stock gauge to display at which RPM the throttle bodies start opening. This bike doesn't have any gauges.

    http://forums.sv650.org/showthread.php?t=55459&highlight=throttle+position+sensor
     
  14. WIslowpoke

    WIslowpoke Well-Known Member

    I have now verified that the TPS is securely attached, couldn't rotate it around the screw, and could only tighten the torx screw by about 1/16 of a turn.
     
  15. E Reed

    E Reed Well-Known Member

    That still doesn't necessarily mean that it's in the correct placement.
     
  16. WIslowpoke

    WIslowpoke Well-Known Member

    Any way to verify without a dash? Apparently the TPS is very touchy for adjustment.
     
  17. E Reed

    E Reed Well-Known Member

    You couldn't get an exact position, but you could do some things to verify that the TPS is or isn't the problem without the dash.

    Does it immediately start revving up as soon as it is started?

    Have you tried starting it without the airbox on it to see if somehow that's the problem?

    Does turning the throttle while running alter the rev's at all?
     
  18. WIslowpoke

    WIslowpoke Well-Known Member

    The WOT condition isn't present anymore. It happened only during and after the one track session, over several start and shut off cycles. Then it stopped, without any intervention in the airbox or the TPS. I rode the bike for another four sessions that day without any issue. The bike starts and responds to the throttle just fine now, and has ever since about 20 minutes after this started happening.

    I can try to start it without the airbox but not sure what that would tell me. The secondary butterflies work fine.
     

Share This Page