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Hard to Start Hot Engine XS650SH

Discussion in 'The Garage' started by Paul Sutton, Dec 19, 2017.

  1. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    These are my rambling "carb thoughts" when contemplating a startup.
    Thinking in terms of what the fuel's doing, has been doing, and will do.

    When sitting cold, carbs cold, fuel cold, difficult to vaporize fuel, use choke.

    After a significant, fully heated ride, carbs are hot and will heatsoak from neighboring engine heat, making them hotter. Hot fuel vaporizes readily when hot, and will give the effect of overrich.

    If a short pause, still hot, carb throat full of fuel vapors, crack throttle for restart, or fully open throttle and kick with ign off to clear the vapors.

    If a longer pause, and engine is just warm, the vapors will still be in there, and starting to condense. Anticipate an overrich startup, crack throttle, or clear it.

    If an even longer pause, and engine temp is close to ambient, vapors probably gone, but may have condensed fuel in the throat. Clearing may not be necessary, but immediately crack throttle after kick to clear the condensation.

    After a short/mild, warm-up ride, engine and carbs not hot, not worried about hovering vapors and overrich. Start normally.

    If start fails after the hot run, suspect fuel fouled plug(s). Do the clearing thing. An old trick to get spark to fire thru fuel foul, pull the plug caps just enuff to have a 1/8"-1/4" gap between the sparkplug's post and the plug cap's connector, forcing the spark to "jump" the gap, which induces a higher initial spark voltage in the plug's gap, firing thru the foul. The foul-blasting "spark gap" contraptions are based on this old racer's trick...
     
  2. I've got a 79 stock XS650 it 2 started fine with electric start wen cold but after 30 mins of rideing will only restart if I put different plugs n it like it's not getting fuel me thoughts
     
    MaxPete likes this.
  3. MaxPete

    MaxPete Life with Lucille...I suggest, she decides. Top Contributor XS650.com Supporter

    Be sure to use the "choke" (which is actually an enricher circuit in the carbs - not a choke in the traditional sense).

    I have never been able to start my XS650 without the choke - unless it has been running within the previous 5-10 minutes. It runs great after a few seconds but it ALWAYS needs the choke to get going - even 20 minutes after a 75 mph freeway blast.

    PRF
     
  4. Paul Sutton

    Paul Sutton Buckhorn Gang Member Top Contributor

    I forgot I ever started this thread. Thank you for all the comments. With the SH I found the best kick-back occured in Winter at close to zero Celsius with the choke fully open. I recommend everyone try this for Christmas.
     
    TwoManyXS1Bs and gggGary like this.
  5. gggGary

    gggGary Stop that! Top Contributor XS650.com Supporter

    My first thought is oil fouling.
     
    Paul Sutton likes this.
  6. xjwmx

    xjwmx XS650 Guru Top Contributor

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    Hard to start when hot can be flooding. Try cranking it with the throttle open. Plugs could be wet with gas or having plugs out lets gas evaporate.
     
    Paul Sutton likes this.
  7. gggGary

    gggGary Stop that! Top Contributor XS650.com Supporter

    check recheck valve clearances.
     
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  8. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    One trick I've been doing for the past few years now, on shutting down a hot engine on a hot day.

    At idling speed, immediately after killing the ignition, crack the throttle 1/4 turn, hold until engine stops (about 1-2 seconds). This clears the carbs, inlets, and plugs.

    Later, startups are a 1-kick affair...
     
    Paul Sutton, gggGary and MaxPete like this.
  9. MaxPete

    MaxPete Life with Lucille...I suggest, she decides. Top Contributor XS650.com Supporter

    Now THAT is a good idea 2M!

    Dang - yer pretty sharp!
     
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  10. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    Haha, well it might *look* that way, Pete.

    Could be that my head is stuck in the '70s.

    This may not work for other bikes...
     
  11. Wats that n how do I fix it
     
  12. That's wT I thought 2 but my plugs r always dry as a bone so idk
     
    MaxPete likes this.
  13. xjwmx

    xjwmx XS650 Guru Top Contributor

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    ^I would have the same problem starting hot sometimes, but it never got so bad as needing new plugs. I think it was Dogbunny on here suggesting the open throttle cranking to somebody, which worked for me too. And I've used it on old cars with carbs back in the day. The only time I needed new plugs to start was when I had sticking float needles from bad gas + bad rubber tips.
     
  14. Brassneck

    Brassneck XS650 Guru

    on my '69 VW, after a drive and the engine is hot, you literally need to step on the pedal (WOT) and hold it there in order to start it up again... it's pretty common for old VW's and translated well to my XS...that is until I switched to VM34's. Now it's a non-issue. Starts up with less than a rotation on the kicker or fraction of a touch to the starter hot or cold. Happy with my decision so far :)
     
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  15. Jim

    Jim I have a plan. It's something to deviate from. Top Contributor XS650.com Supporter

    Had a 59 Karmman Ghia and several Bugs that did the same. Was caused by vapor lock. Wrapping the fuel line with aluminum foil cured it on all of 'em.
     
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  16. Brassneck

    Brassneck XS650 Guru

    Cool...will need to give that a try. How much foil did you use?
     
  17. I tryed the open throttle at kill n it seems to be working I'm do leak down now n check float highth again thanks everyone
     
    MaxPete likes this.
  18. Jim

    Jim I have a plan. It's something to deviate from. Top Contributor XS650.com Supporter

    Was way back in the 70's... :umm:
    I think I doubled it, then wrapped that around 3 or 4 times.
     
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