'84 VF500F has little power, dies quickly

Discussion in '1st & 2nd Generation 1983-1989' started by RoninUnderground, Jan 15, 2014.

  1. RoninUnderground

    RoninUnderground New Member

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    The bike started losing power, for a while I could keep it running by lowering my speed. It seemed at first as if it was running out of fuel, I have a gravity feed with in line filter so I thought maybe it was clogging. The problem worsened over a few hundred miles to where when I could get it to start it couldn't even move under its own power before dying. Now when it'll start throttle response is horrible and it'll eventually die regardless of choke and throttle positions. I've tested the ignition coils and they were out of spec, but about the same so I'm wondering if they'd both be bad by the same amount... I also swapped in some same model coils from a parts bike ('83 VF750, coils tested about the same as the ones on the VF500F). I tested the pulse generator, it's about freezing outside and the coils came back about 345 Ohms, right about the middle of the spec'd range. Honda doesn't give testing procedures for the spark unit so I bought a used one online, it has a slightly different model number, but the bike acts the same with either installed. I swapped in the R/R unit from the parts bike as well, same result. I installed new spark plugs, fuel flows freely from the tank. I'm at a loss. I put about something like 6000 miles on it since I bought it this summer and I'm itching to saddle back up asap. Any ideas as to what's wrong with it?
     
  2. Rollin_Again

    Rollin_Again Member

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    Have you checked for air leaks in the fuel system? How do the carb boots look and is there fuel in the carb bowls?


    Rollin
     
  3. Allyance

    Allyance Insider

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    Since this problem has worsened gradually, I would agree with Rollin, fuel supply (common to all 4 carbs), air supply, too much (cracked boots) or too little, make sure little critters haven't nested in air box! I doubt compression with two heads. Does it run like some cylinders are firing and some aren't, or just blah?
     
  4. RoninUnderground

    RoninUnderground New Member

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    Last I looked the carb boots looked pretty good, but since I'll probably have to pull them to check the bowls I'll make a point to check when I do.

    How would I check for air leaks in the fuel system? (cracked boots are easy to look for, but is there something else I should be checking?)
     
  5. Allyance

    Allyance Insider

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    As you said, gas is gravity fed. Pull Line off carbs and check flow in to a jar. Check for water in gas, dirt. Filter look clean, plenty of gas in it? Got to be something simple. If I remember right, there are brass drain screws at the base of the bowls, bleed gas into clean glass jar or glass to see if contaminated.

    Did you check your air box? WE had little friends that loved to nest in our Audi's V6 engine! Nice and warm after a short ride home from work.
     
  6. RoninUnderground

    RoninUnderground New Member

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    I opened the air box completely when the problem struck, it was fine save for a little oil, probably from what I think is the PCV. There shouldn't have been water in the gas as I'd put fresh fuel in it several times as the problem worsened. This problem developed and came to a head all during a 1000+ mile road trip. The fuel filter is new, changing it didn't help. I did order a generic fuel pump on someone's recommendation I found searching this forum, but I won't install it until it's warmer and I've sorted out the current problem.

    I'll check the carbs as soon as I can. I have work and classes started this week so things are busy once again, but I do really want to ride. My truck sucks down gas too fast.
     
  7. MPH Racing

    MPH Racing New Member

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    If the bike will idle then let it run for a few minutes and check how hot the cylinders are. Just put your hand close to each of them and if they are cold or cool you could have the same problem I did. I took the carbs off to clean them and found my jets in the back 2 carbs had fallen out and were sitting in the fuel bowl. My other 500 had almost the same problem but that ended up being one of the balancing screws fell out and didn't have any power on the way home one night.
     
  8. Rollin_Again

    Rollin_Again Member

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    The most common and simple way to check for air leaks is to GENTLY spray starting fluid around the carb boots while the bike is idling. If you have an air leak the starter fluid will be drawn into the fuel system and the RPM's should increase slightly. Be sure to have a fire extinguisher handy if you attempt to do this and use the starting fluid sparingly since not much is needed.


    Rollin
     
  9. creaky

    creaky New Member

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    Agree that the problem is fuel delivery. 1st, check fuel flow from the petcock. If that is OK, turn on the petcock, wait a few minutes, then open the bowl drain screws one at a time to see if the bowls are actually filling with fuel.
    Also check is the fuel cap vent. If it is blocked, fuel flow from the tank will be very little to none.
     
  10. crustyrider

    crustyrider New Member

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    you said petcock :pound:


    if your pulling the carbs off you might as well clean them.. sounds like it is a simple fix...
     
  11. squirrelman

    squirrelman Member

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    Any rust in the fuel tank ?? Drain it and flush to remove any crud, good once-a-year periodic maintenance and something you'd want to do on any just-bought bike or before replacing cleaned carbs as a precaution. Water can condense in tank or you might have purchased watery gas, which sinks to the bottom.

    If you open a bowl drain, water comes out in little blobs unlike pure fuel if water's present.

    That bike has 2 CDI boxes, i believe, and either one could fail, knocking out 2 cylinders i think.
     
    Last edited: Jan 16, 2014
  12. RoninUnderground

    RoninUnderground New Member

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    Hey guys, haven't forgotten I've just been busy. When I get the chance I'll clean the carbs and return with the results. Thanks!

    Also I picked up a 2001 VFR800Fi really cheap. I'm sure many of you know that bike is NUTS in comparison lol
     
  13. Rocker1500

    Rocker1500 New Member

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    I believe your petcock is vacuum operated, correct? It's possible that this has stopped working. I had another bike and when the vacuum stopped working it would randomly die at highway speeds. There's a way to take out the vacuum mechanism all together. Not sure if you have done this yet or not. The petcock on my vf500 was converted to just be on all the time (secondary inline fuel valve was installed).

    vf500-petcock.jpg
     
  14. RoninUnderground

    RoninUnderground New Member

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    Strange, I was able to get fuel to flow by applying positive pressure to that nipple so I figured that's how it worked...

    I may be selling the bike soon anyway since I have 4 bikes now and need money, I'll definitely miss it though.
     
  15. RoninUnderground

    RoninUnderground New Member

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    Update: did a valve adjustment, now she runs. First valve adjustment I've ever done. Now, the clearance values are for between the cam and rocker arm, not between the rocker arms and valve stems, right?
     
  16. squirrelman

    squirrelman Member

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    What's illustrated in the Honda service manual ?? Dija check valve tops for signs of distress, mushrooming ??
     
  17. RoninUnderground

    RoninUnderground New Member

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    Well, at TDC for each cylinder. I did glean that much from the FSM.
     
  18. squirrelman

    squirrelman Member

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    Dija do a compression test to possibly explain the lowish power ??
     
  19. RoninUnderground

    RoninUnderground New Member

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    God. Fucking. Dammit.

    [​IMG]

    I guess I'll look closer when I go do it again. Shit. It wasn't horrible though. Carried two of us up to 85-90mph without too much trouble. I think I still have the +1 sprocket on the front so I wasn't really surprised at it's power.
     
  20. RoninUnderground

    RoninUnderground New Member

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    I redid it and it runs a bit better. Probably still needs a carb sync. Valve stem heads looked fine to me. Then traded the bike for a 1911. It's been fun, thanks for the help :) I still have and love my '01 VFR800.
     
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