84 VT 500 highway crapping out issue...

Discussion in 'Road Warriors' started by YAHBO, Oct 28, 2013.

  1. YAHBO

    YAHBO Grip and rip since 1983

    Joined:
    Nov 9, 2004
    Oddometer:
    823
    Location:
    Eastern Long Island, NY
    Buddy of mine has the V twin Ascot...runs fine around town. At 60 mph and above, the bike shudders and craps out. Every time. Below 60, ride it all day. Above? It stalls and he has to pull off the road and wait ten minutes til it cools down and then it runs fine.

    He checked the following:

    Coils (new)
    Carbs (cleaned)
    All hoses (checked and double checked routing)

    Left to do as far as easy stuff:

    Plugs
    Gas quality/freshness

    Any ideas?
    #1
  2. TrashCan

    TrashCan Scary Jerry

    Joined:
    Oct 5, 2005
    Oddometer:
    4,938
    Location:
    Louisville, Tn
    Fuel cap venting???
    #2
  3. Hughlysses

    Hughlysses Long timer

    Joined:
    Jun 2, 2004
    Oddometer:
    3,445
    Location:
    Summerville, SC
    My first guess would have been ignition coils (a notorious problem on older VT500's) but since he's installed new that's out. He did install NEW coils, right? Not used ones purchased off ebay?

    Tank venting issue seems like the next most likely thing. Easy enough to check- the next time it happens, immediately pop the cap on the gas tank and see if the bike will fire up without waiting 10 minutes.

    I also wonder if it could be a vacuum petcock issue. If the diaphragm is marginal in the petcock, there may not be enough vacuum at high throttle openings to keep it open (?). My 83 has the manual petcock so I'm guessing here.
    #3
  4. RedRocket

    RedRocket Yeah! I want Cheesy Poofs

    Joined:
    Feb 28, 2003
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    20,580
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    SoCal
    I had on old Suzuki that did that.
    In this case the vacuum powered petcock needed replacing, it was unable to draw enough fuel at higher speeds.
    #4
  5. kraven

    kraven Hegelian Scum

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    Asheville NC
    This.

    And this. Just because they were recently installed and purchased doesn't mean they're good. A lot of electrical components that fit are shit on the inside compared to the OEM stuff. Best to pull them out of the box and meter them.
    I started doing this about 15 years ago with plug wires and coils when I started having "I just replaced that!" problems on cars and bikes. There's a lot of Chicom or Taiwan crap out there that isn't up to par. You may have some of it.

    A tow truck will cost more than these coils, so spend coin on the best parts you can find, not eBay junk.
    #5
  6. YAHBO

    YAHBO Grip and rip since 1983

    Joined:
    Nov 9, 2004
    Oddometer:
    823
    Location:
    Eastern Long Island, NY
    Thank you for the help, gentlemen. I have relayed these ideas to my buddy and he assures me the coils are genuine Honda, it stalls with the cap open as he has experimented with the venting possibility, and that his next plan of action is replacing the petcock.

    I will post up his results after the petcock replacement.
    #6
  7. kraven

    kraven Hegelian Scum

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    Asheville NC
    Good luck, bro. :1drink
    #7
  8. Hughlysses

    Hughlysses Long timer

    Joined:
    Jun 2, 2004
    Oddometer:
    3,445
    Location:
    Summerville, SC
    I seem to recall that the vacuum actuated petcock used on the 84 Ascot is NLA from Honda, but it'd be worth checking. Another alternative is that someone may make a repair kit. If all else fails, I'm pretty sure he can get a universal manual petcock (as used on the 1983 VT500FT) from several sources. He'll just have to plug the unused vacuum line(s).
    #8