Idling motor, blip throttle, then suddenly motor revs to 4k and stays?

Discussion in 'Carb/Tuning' started by c0zgrove, Apr 8, 2019.

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  1. Apr 17, 2019 #21

    c0zgrove

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    I make sure to do this every time I reconnect the cables
     
  2. Apr 17, 2019 #22

    Woody

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    I had a similar problem a few years ago.my bike would idle fine.on the kick stand.But when I stood the bike upright. The rpms would raise roughly 3k more. My problem ended up being. 4 lil black o ring's. These are not just o ring's. They have a tapper
    On one side. I can't remember what they do. But do know. New ones installed.And no more issues.
     
  3. Apr 17, 2019 #23

    c0zgrove

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    Do you remember which o-rings they were?
     
  4. Apr 17, 2019 #24

    Woody

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    I think they are on the jet block.or have something to do with it.
     
  5. Apr 18, 2019 #25

    tugla

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    I had a similar issue yrs back chased it for a long time.

    With the bike not running when you twist the throttle does it snap back closed with authority ?
    Next i had to do a full tear down of the carbs and clean as the littles bits of junk was causing my similar issues...once done never had the issue again.

    Dannymax offers a great cleaning service here if need be.
     
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  6. Apr 18, 2019 #26

    c0zgrove

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    Yea it does. I've been able to recreate the problem with and without throttle cables connected at the carbs. I think next I'm just going to completely disassemble the carbs and look for potential problems.
     
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  7. Apr 19, 2019 #27

    Fire-medic

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    I'm guessing that the post about four little o rings and the jet block is for the brass pipe that goes through the middle of the jet block. it's the needle seat for the throttle needle. there is a very thin o-ring that goes on that before the Jet block goes into place: first your gasket, then the skinny o-ring on the brass tube then the jet block, then the screw to hold the jet block in place. I think it's called the emulsion tube. Ok, it's the "main nozzle " on the Ron Ayres fiche part #34 & the o ring is part #33. The jet block gasket is #35, good to have 4 on hand for a carb tear-down.
     
    Last edited: Apr 19, 2019
  8. Apr 19, 2019 #28

    Fire-medic

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    I forgot. did you use a can of starting fluid sprayed on everywhere around the carburetors and the V boost system and the rubber boots for the carburetors? Checking for air leaks?
     
  9. Apr 20, 2019 #29

    dannymax

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    The OP mentioned the o-rings having a 'tapper'....the only rubber parts in the float chamber/jet block area are the thin E-tube o-ring you mentioned and the (2) rubber plugs at the bottom of the jet block. Nothing that might be referred to as a 'tapper'??
     
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  10. Apr 20, 2019 #30

    Fire-medic

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    The only 'tappers' I know of are kegs of beer!

    If the 'King of Carburetors' is stumped, that's sayin' somethin'!

    The air idle screw, with its spring, flat washer, and o-ring, all of which do have an effect on idle quality, is about the only other thing I can think-of.
     
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  11. Apr 20, 2019 #31

    Woody

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    I think your right.as far as emulsion tube o rings. Look close at them.they are beveled on 1 side. Regular o ring's won't work.
     
  12. Apr 20, 2019 #32

    c0zgrove

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    Alright guys, I think I've got it all working now. Unfortunately I can't really say exactly what fixed the problem because I think it was likely a combination of things. However, I completely rebuild the carbs today and replaced all the rubber inside as well as the idle mixture screws and enrichers. When I tore into everything I did notice one of the enricher diaphragms had some tiny holes in it so that may have been the last thing that was causing the phantom high idle to happen. Thanks to everyone for your suggestions, thanks to you there's one more VMAX still on the road!
     
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  13. Apr 21, 2019 #33

    dannymax

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    A 'beveled' o-ring? They become beveled after a few years of the jet block pressing on them but from the factory? Nope, they're round just like all other o-rings. Any o-ring of the proper dimensions will work in that application.
     
  14. Apr 21, 2019 #34

    Woody

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    The ones we bought at the local Yamaha shop.( in factory sealed packaging) had a slight bevel.
    It fixed my problem. Are the beveled o rings an 85 thing ?
    I'm baffled.
     
  15. Apr 23, 2019 #35

    dannymax

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    Got a part number?
     
  16. Apr 24, 2019 #36

    Fire-medic

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    20190424_140700.jpg 20190424_141239.jpg Yeah, I'd think they take a 'job-set' and that's where the bevel comes-from.

    "Tapper" = "taper."

    Here is proof: (attachments)

    One is obviously 'beveled.'

    One is round-contour.

    I'll leave it to you to determine which is the used o-ring, and which is the new o-ring for under the jet block, on the brass emulsion tube.
    20190424_141319.jpg
     
    Last edited: Apr 24, 2019
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  17. Apr 25, 2019 #37

    dannymax

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    "Job-set" Good term Philip, describes the situation to a 'T'.
     
  18. Apr 25, 2019 #38

    Fire-medic

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    I'm appreciative of the feedback, dammymax, thankew! I believe the photos put this to-rest. My cellphone pics are with a broken lens, sorry, folks.
     
  19. Apr 25, 2019 #39

    Woody

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    All I know is I tried new round o rings. Same size but not factory part.had idle problems.bike would be fine on side stand.then stand it upright. And again 3k rpms.
    The next day. I got new ones from the dealership. I noticed the new ones had slight bevel.and they fixed the issue.didn't know this was a big deal.I was just giving the guy. Another thing he might have overlooked. Don't know why the ones I got had a beveled edge.
     

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