Troubled '86 vf500f

Discussion in '1st & 2nd Generation 1983-1989' started by Sirfoxx14, Jun 5, 2021.

  1. Sirfoxx14

    Sirfoxx14 New Member

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    Hello-

    Been attempting to make progress with my interceptor. I am having an issue where random cylinders are cutting out while I'm riding. This is easy to feel while riding, as well as listening to the constant backfiring out the mufflers. Usually when its warming up it will rev fine will on the stand. However, as soon as you start riding is where the issues start to appear. I've had to limp the bike back home several times on what feels like 1 cylinder -- full throttle just to do 5mph

    My brother went through and rebuilt the carbs and replaced the spark plugs, wires, and boots, so those are less likely to be the issue imo...though he did mention that when he had the floats set to honda's spec, gas would pour out of the carbs and down into the motor. He ended up adjusting them till they quit dumping gas out of the carbs...again, I dont think this is the issue as all these issues im having seem to crop up and get worse as the bike gets hotter.

    I first thought it was bad ignition boxes. Purchased a set off ebay that claimed "came from a running bike". Slapped them on, same issue.

    I then started looking at the pulse generators. They tested out of spec, so I managed to find a set that were still within honda's acceptable spec range. Same problem.

    Tested ignition coils. Both were out of spec by a good margin. Replaced with a spare set that are super close to honda's acceptable range. Also replaced the ignition boxes with another spare set I just picked up at the same time. Better, but now it is intermittently firing on 4 cylinders with what seems like its running fairly consistently on 3 cylinders with backfiring coming from the right side. I've had the back exhibit these same symptoms only for it to go back to running on 1 cylinder if left overnight.

    I am at a total loss at what to do. I dont want to spend money on new ignition boxes or attempt to source NLA ignition coils. Any input would greatly be appreciated!
     
  2. raYzerman

    raYzerman Insider

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    Have you checked all the ground wire points, I'd start there and make sure everything is clean and tight.
     
  3. Diving Pete

    Diving Pete Member

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    I going to suggest earths, carbs, & coils - in that order.

    The fact that once you introduce heat into the equation it gets worse then something isn't happy. lol

    Check the main earth for the front coils & even look into adding an extra earth to it - try to eliminate one of these at a time.
     
  4. Cherryriver

    Cherryriver New Member

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    Kind of late to this thread, but- any chance it's fuel starvation from the fuel cap vent being clogged? I know it's a stretch, but parts of the story fit.
    The symptoms described come somewhat close to what I went through on my '86 when I first got it running.
    On the other hand, so many of the electrical problems on bikes do come from bad grounds (or earths, as they say), and not just antiques.
    Ask a second-gen FJR rider about "ground spider" failures: melted gang-grounding sockets killing the bike dead on the road.
    Coming from the olden days- note the '66 Velo in the avatar- grounds were a worse problem then. Some bikes had the headlight and instruments grounded through the steering head bearings. What could go wrong?
    I normally create a new grounding post somewhere on any bike falling into my clutches and run plenty of black wires hither and yon.
     
  5. squirrelman

    squirrelman Member

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    replace the float needles. your feckless brother may have set float levels incorrectly to try to compensate for leaky needles, never a good idea.
     
    Last edited: Jul 27, 2021
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