1. Dismiss Notice
  2. Dismiss Notice
  3. Hey Facebook people... We've created a group for XS400.com members to connect. Check it out!
    Dismiss Notice
  4. Want an XS400.com t-shirt? Go to the store to order. Limited sizes and quantities available.
    Dismiss Notice

Over revvvvvvv... like full throttle at idle

Discussion in 'The Garage' started by Sharkins123, Aug 11, 2019.

  1. Sharkins123

    Sharkins123 XS400 New Member

    1
    0
    1
    Toronto
    Hey all,

    First post... after reading a million threads first. My boy bought an 82 XS400 (I think). And as true bike neophytes, we've screwed 10 things up on it and fixed half of them!

    Here's my latest, weird issue maybe you good folks can help with. When we start the bike it kicks into over rev as though the throttle is fully open. Throttle/cables, etc are all mechanically sound...

    Thanks for any insights you may have. This machine will run one way or another... even if it costs thousands! It's an illogical matter of pride at this point.
     
  2. SoulMan

    SoulMan XS400 Addict

    Check for leak around the carb boots by spraying carb cleaner in that area.
     
  3. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    Did you check the idle set screw between the carbs? Enrichener/choke stuck?

    If you removed the carbs and took them off the bracket, they would definitely need to be synced up again. The master carb could be adjusted way too high.

    Vacuum leaks at the boots will make idle high. Replacing the boots is practically required when you start to dig into these machines. If they have any cracks at al, replace them.
     
  4. Carb boots. Carb clean, carb synch. How many turns out are your screws? Pictures or we don't believe you own one ;)
     
  5. CableGuy

    CableGuy XS400 Member

    18
    3
    3
    Iowa
    Does that bike have a vacuum petcock? That's what happened when mine failed. Poured gas straight in.
     
  6. Carb would stop petcock from doing that if float correctly set.
     
  7. CableGuy

    CableGuy XS400 Member

    18
    3
    3
    Iowa
    I have no idea what I am doing 89% of the time, not a mechanic. I do know I was going about 25mphs and almost ended up in the back of a car cause the engine went wide open. When I took off the vacuum line between the petcock and carb holder boot, gas was pouring out. Capped that on both sides and it runs as advertised. So now I just drive in the prime position. Probably a better way to do it.
     
  8. BBS360

    BBS360 XS400 Guru Top Contributor

    Yeah, if the diaphragm in the petcock degrades you can get fuel out the vacuum line, bypassing the carbs entirely.
     
  9. SoulMan

    SoulMan XS400 Addict

    Wow that is pretty scary. Considering the age of these motorcycles I might just drive in the prime position without the petcock vac line also. Something to consider.
     
  10. xschris

    xschris a lifestyle not a trend Top Contributor

    If your diaphragm is bad it will flow on any position.
     
  11. CableGuy

    CableGuy XS400 Member

    18
    3
    3
    Iowa
    I thought it should be that way, but it doesn't. If I forget to turn it to prime, I run out of gas. Sorry, don't mean to steal the thread.
     
  12. Glad you're safe and thanks for the heads up! Most of us aren't mechanics and I didn't realize it could free flow through vacuum. Yikes
     

Share This Page