'86 700 stumbling and quitting

Discussion in 'Mechanics Garage' started by GKVFR, Aug 13, 2021.

  1. GKVFR

    GKVFR New Member

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    Greetings once again VFR people. It has been many months since I have been on the site (I am not a social media person), and now I am not able to find the conversation that I initiated back then... Anyway. I came to this site looking for input on a problem with my '86 700, where it would stutter and then stall during my morning commute. The excellent replies I received pointed me towards ignition, suggesting I replace the cam pulse generator sensor. I figured I would simply remove said sensor from one of my two parts bikes, but it turns out that the cam pulse sensor is an 1986-only item, and both of my parts bikes are 87s. So that rules that out. But in examining what was happening I realized that my problem is fuel, not ignition. I have found that when the engine starts to stumble I can usually keep it going by simply going to full choke for a few miles, and then all is good once again. I really think taking the carbs apart is the way to go to solving this problem - now to actually tackle that project.
    And I have to mention - this week I turned 199,000 miles on the beast. With my normal commute of fifty miles a day that means that in another month I will hit 200,000. Kinda stoked about that. I look forward to taking a photo of the bike with me and my two sons again, recreating the one I took of us when I cleared 100,000 back in 20007. Good stuff
     
  2. Captain 80s

    Captain 80s Member

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    Keep us posted. They are such good motors. Normally carb problems don't come and go like you describe, but I think it is still the right path to absolutely verify everything before moving on if needed.

    And you're a time traveler!!! Back to the Future!
     
  3. weevee

    weevee New Member

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    If the carbs are similar to the Keihins on my 750, check the tiny rubber o-rings haven't perished around the tips of the pilot jets. The jets are screwed into the same passage that supplies fuel to the choke, so air being sucked past those o-rings will weaken the mixture. Pulling the choke offers temporary compensation.
     
  4. squirrelman

    squirrelman Member

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    nice try to help........... but the mixture screw o-rings would have little to NO EFFECT on the problem the poster describes, and the choke enrichment circuit does NOT go through there. at crusing speed there isn't much the mixture screw passage does, and some VFR mixture screws have a second O-ring to further prevent air ingress.

    instead, i think the problem may be related to slow, partly-obstructed gas flow from the tank petcock. so i'd suggest pulling off the fuel line on the tank TO the pump and checking for a full, free flow into a can with petcock switched ON. if debris has collected on the pickup screen a reverse blow INTO that line may clear it.

    CONGRATS to the man who has nursed his '86 to 200k ! good work !
     
    Last edited: Aug 13, 2021
  5. Captain 80s

    Captain 80s Member

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    The two other 86 VFR I personally witnessed go well over 100K weren't nursed, that's for damn sure. Just regular maintenence, no major repairs. Ridden HARD. ALL THE TIME.
     
  6. TOE CUTTER

    TOE CUTTER Mullet Man

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    Given the miles it may just be time to clean the entire fuel system. You must have pumped some funk into it over the years.
    Stumbling and quitting sounds like the title of my autobiography.
     
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  7. weevee

    weevee New Member

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    Didn't mean to confuse the OP, but yes, I worded my reply wrongly. The picture shows what I mean. Both the pilot circuit and the choke circuit feed into opposite sides of the carb's throat. A pilot (fuel screw) that's actually allowing more air to pass than fuel will weaken the mixture, whereas opening the choke will flood the carb's throat with fuel. I appreciate this is not a scientific explanation ~ and I realise the main jet supplies the bulk of the fuel at higher revs ~ but I found this to be the issue when my VFR would only run on choke even when hot. It costs a pittance to replace those o-rings, so it wouldn't hurt to check them. Air leaking into the intake from anywhere else could have a similar effect ~ so it may be worth checking for splits in the rubber boots that attach the carbs, too.

    [​IMG]
     
  8. squirrelman

    squirrelman Member

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    ^%^ yes! it's good to drain and flush a fuel tank at least every 2 years.

    OMG, weevee, u got RC30 carbs ????
     
  9. weevee

    weevee New Member

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    Yes ~ and the rest of the bike to go with them :Dance:
     
    Last edited: Aug 16, 2021
  10. jethro

    jethro New Member

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    Have you eliminated the chance that you have water in your fuel?
     
  11. GKVFR

    GKVFR New Member

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    Greetings once again VFR people. I have a few updates : my mighty beast did-in-fact turn 200,000 miles last week. Flippin awesome. Now on to the next 100k !
    As far as my stumbling/stalling issue : For the past few months there had been an obvious issue with my charging system, evident by the occasional slightly-slower starting. I was dealing with the problem by simply throwing my battery tender on over night every-other night. But of course I managed to skip a charging session; the engine started OK that morning but cranked just a bit slower for the trip home from work. Just 3 1/2 miles from home I pulled in the clutch at a stop sign and it completely died - not even the neutral light was on. Once back home and forced to dig into the problem I found the voltage regulator connector obviously 'smoked'. I replaced the unit using the regulator from one of my parts bikes and have had zero stalling problems since. That being the fix makes really no sense, as every indicator pointed to the problem being fuel related. But I am not complaining ! Stay tuned
     
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