Flat spot

Discussion in '1st & 2nd Generation 1983-1989' started by MFTIC, Sep 30, 2018.

  1. MFTIC

    MFTIC New Member

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    Problem - When the engine should be kicking in (around 6k rpm) there is a flat spot/loss of power. Bike will keep speeding up but slowly. Almost like there is no difference between half throttle and on?
    I'm thinking maybe a clogged main jet?
    Ordered a fuel filter but pretty sure that is not it. Any other ideas? I'm afraid to break into the carbs and look, lol) I've worked on dirt bikes with one carb, don't understand the 4 carb thing, haha

    Extra NON-pertinent info.
    Bike had been sitting for 4 months with the gas drained from the bowl and most of the tank in garage. New gas put in and bike ran for more than 40 miles in current condition.
    Starts awesome, idles awesome, runs up to around 6k rpm awesome.
    Also i would like to sell this bike. Already have a replacement. Found a great kid that knows his shit and wanted to buy it before we discovered this problem. He's hesitant to spend money on it when not really sure about the problem which i totally agree with.
     
  2. Captain 80s

    Captain 80s Member

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    Did you verify the condition of the air filter? And also make sure the air box isn't full of dog food or nuts from a rodent?

    The fact that it starts and idles so nicely (and thats the smal jet) I highly doubt you have a clogged main jet(s).
     
  3. MFTIC

    MFTIC New Member

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    I thought of that but didn't check as it's been in the garage and the cat goes that way daily. Good call. I will check! I have a few days until the fuel filter arrives becuase i'm a moron and ordered off of Amazon and not the local auto parts store.
     
  4. MFTIC

    MFTIC New Member

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    Just looked and all is spotless. No misses when running, just that bog and loss of power. RPM's change depending on what gear i'm in but usually right around there. That's why i attribute it to half throttle or more.
     
  5. Captain 80s

    Captain 80s Member

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    Just for giggles, jump the fuel pump relay to eliminate it.
     
  6. MFTIC

    MFTIC New Member

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    What's that do, why would I do that, and most importantly how, lol

    Sent from my Pixel XL using Tapatalk
     
  7. Captain 80s

    Captain 80s Member

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    The relay is what allows the pump to operate. They are widely known to be a weak link. Usually they fail completely, but I have seen them fail partially. It might not be allowing your pump to keep up with demand. Under your left side cover next to your winker relay. Disconnect it from the harness and use a jumper wire to bypass it. Can remember which 2 colors to connect off the top of my head. Just try a few combos until you here the pump start. The relay is a safely feature, the pump will operate normally. It's just a super easy thing to do and eliminate a possibility.
     
  8. squirrelman

    squirrelman Member

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    Blue/Black to Black

    yellow not connected
     
  9. MFTIC

    MFTIC New Member

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    So I think i understand now. Jump those 2 wires then go test ride it? Damn i can be slow sometimes. LOL.
    *I'll try to do this tonight. Otherwise it will have to wait till this weekend. Will also have the filter by then hopefully.
    Thanks guys! fingers crossed.
     
  10. Captain 80s

    Captain 80s Member

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    Yes, that's it. Paperclip or some heavy gage wire and some tape can work. If you don't get it right you won't go far anyway. With the key on, the pump should start priming when jumped.
     
  11. MFTIC

    MFTIC New Member

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    IMG_20181001_174740.jpg Think i found the relay. Jumping the white and black seem to engage the pump. Very loud clicking, not the whirl i was expecting. Didn't get to test ride it but i didn't notice a difference between relay hooked up and wires jumped. Couldn't hear anything over the engine but notice a blurble in the filter like every couple seconds. Filter does not fill up but I figure that is normal.
    So I guess the relay is good. Maybe the fuel pump itself?

    **EDIT...I found the section on testing fuel pump flow. Will try that this weekend.
     
    Last edited: Oct 1, 2018
  12. Captain 80s

    Captain 80s Member

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    Filters will not necessarily fill up.

    That doesn't prove your relay is good. Like I said, I've seen them partially work. And with the relay installed, the pump will not work when you just turn on the key. The bike has to be either being cranked with start button or the engine running.

    Just take the damn thing for a ride.
     
  13. MFTIC

    MFTIC New Member

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    Lol, took it for a ride. Same thing, no change. I don't think it's a fuel to the carb issue but will test the pump this weekend and install new filter. My mind is still on main jet but hoping it's not and someone comes up with an easy/cheap fix

    Sent from my Pixel XL using Tapatalk
     
  14. Captain 80s

    Captain 80s Member

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    Well it was easy to confirm that's not it. I am leaning towards the carbs needing some general love, but will be surprised if it is actually the main jets that are slightly blocked and everything else fine.
     
  15. sixdog

    sixdog New Member

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    I agree with The Captain, also check for intake leaks before the carbs and after the carbs. Take a good look at your intake boots. Check for good slide operation as well....basically like stated...give the carbs some love!
     
  16. squirrelman

    squirrelman Member

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    MYFTIC, i might be able to help. :Yo:

    As an old guy who's worked on sports car and motorcycle carbs for over 45 years, i'd be able to give your carbys the love and special treatment they deserve and have fixed dozens of VF/VFR carbs for members here, many damaged by sloppy and woefully inept previously- attempted repairs.

    exactly how a recent VTR carb set came in:

    july 25-18 021.JPG

    Real beauties , eh !?




    i replace rubber with all new Viton O-rings, float bowl gaskets, cleaned (using chemical+ultrasonic+manual), floats set and verified, leak-tested, mixture screws set, 2 synch-tests for best setting and good idle, fast 10-day turnaround available if necessary.

    Please PM me for any carb cleans/repairs or maintenance.
    Sorry i don't have a Glossy Website :Juggle: but i do dependable work and aim for first-time 100% repair success, a big time-saver for busy D-I-Y guys who might not get it right once or twice or never. Experience counts for almost everything when fussing w. carbs.

    Have some used spare VF/ VFR carb part available for sale or repairs. PM or call 716 836-0154 with ???'s.
     
    Last edited: Oct 8, 2018
  17. Captain 80s

    Captain 80s Member

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    Everybody thinks they can nail V4 carbs. They are weird. Squirrel is not being cute when he says 2nd and 3rd attempts without success. It's from reading posts after posts from people not taking advice and chasing their tail.

    Sometimes you need to let the people that can, do. And the right parts are key.

    Read. Read some more. Then consider just having it done right and spend your energy on something else.

    Squirrel is good.

    This is not a dig at anybody's mechanical abilities. Really, its for anybody reading this and wondering if they can/should.
     
  18. MFTIC

    MFTIC New Member

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    Thanks guys. Funny i did a search an Squirrel came up a couple of times. Already PM,ed him that i'm in a holding pattern. Recently reached out to a friends dad that used to run the motor pool of the local PD. I've had him do a little work on another bike i used to own, cool guy. See if he wants a little project. If not then off comes that carb and Squirrel will have a project.
    *just ran around town this weekend putting 40 mad miles on the bike. I can almost convince myself it's always been like this. Also realized that this idiot didn't understand the four carb thing. Drained the main one where the fuel line enters from the tank and thought that was it and let the bike sit for 4 months. Guessing that is what the problem is.
     
  19. squirrelman

    squirrelman Member

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    Ready anytime ! :thumbs:
     
  20. MFTIC

    MFTIC New Member

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    Wow, that popped off way easy. Only had time for one beer.[​IMG]

    Sent from my Pixel XL using Tapatalk
     
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