'86 VF500F2 - Idle drops at temperature?

Discussion in '1st & 2nd Generation 1983-1989' started by Mukuul, Apr 21, 2020.

  1. Mukuul

    Mukuul New Member

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    Hi everybody.

    I recently acquired myself a 1986 VF500F2.

    I had it for half a day, and then the vacuum membrane in the petcock gave out, so i rebuild that. And upon putting it back together, i decided to clean the carbs. I read all about it and was prepared, but to my surprise getting them off and on wasn't that big of a deal, all things considered, and i could see that the previous owner had taken good care of it, as they were mostly spotless.

    Now to the issue at hand.

    When the bike get warm, or even hot, the idle drops, and if i am not careful as i come to a stop, it will die on me.
    It starts right back up again, and idle's at the lower RPM's, compared to the 1300 RPM's when cold, as it just got off choke.

    Any ideas?

    My thought is that it might be running a little lean on the idle circuit, but i think i also read somewhere that is problem could stem from the pulse generator going bad from head soak

    Anyway, any input would be greatly appreciated.
     
  2. Captain 80s

    Captain 80s Member

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    Have you set the correct idle at operating temperature (like the manual states) and see how it does during the warm up period?

    Lean will "typically" give you a hanging, high idle. Get some starting fluid and with the bike running spray it around your carbs, especially the carb boots, and see if the idle changes. You can at least check for any intake leaks and go from there.

    What size pilot/main jets did it have? Stock exhaust?
    What did you set the mixture screws at after removing them to verify that circuit is clean?
    Did you perform a bench synch before re-installing or did you do that after with gauges?
    Were the needles shimmed at all?

    And of course assuming any basic tune-up items have been check/replaced.

    And most importantly, we can't assess shit without seeing a picture. Missed out on the first post pic. Shame.

    Welcome and good luck!
     
    Last edited: Apr 21, 2020
  3. Mukuul

    Mukuul New Member

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    Sorry for not introducing myself, I was just so eager to get this underway. I don't think it's an lean issue anyway.

    I cleaned the carbs good with a guitar string through every hole, including the pilot screws.
    Stock exhausts, and I think stock jets, didn't check.

    Will check for air leak tomorrow.
    Mixture screws set at 2 and 1/4 turns out as per the manual.
    Carbs not synced, will probably buy a sync tool.

    No shims.

    After warmup I set the idle at 1500, then when it gets warmer the idle drops. Thinking about maybe it only runs on 2 cyl. it is low on power, and struggles to get over 110kmph. Will check the header pipes.

    Just measured the pulse generator, and it reads 362ohm on both when cold, will check when hot.
    Will check coil resistance as well.

    Part of my left side cover is melted. Weird right?

    And lastly, pictures.[​IMG][​IMG][​IMG]

    Sent from my ONEPLUS A5010 using Tapatalk
     
    Last edited: Apr 28, 2020
  4. straycat

    straycat New Member

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    Is that melted area close to the Reg/Rec or the connector for the Reg/Rec ? they're prone to melting connectors, maybe your side panel got some collateral damage. Whats immediately behind that part of the panel ?
     
  5. Mukuul

    Mukuul New Member

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    I took a quick photo, it's raining like crazy here in Copenhagen. But there doesn't seem to be anything directly behind the melted part.

    I can see the cable from the PG is touching the cylinder, that can't be good when I'm having trouble at temp. Plus the cable has a crack.

    Cleaned all the connectors, I'll see how she runs tomorrow if it ain't raining.

    The PO replaced the collector box from the exhaust at some point, so it could be because exhaust fumes perhaps?

    [​IMG][​IMG]

    Sent from my ONEPLUS A5010 using Tapatalk
     
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