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CV carbs rejetting for altitude changes?

Discussion in 'Motorcycle Tech Talk' started by James Powers, Oct 2, 2018.

  1. Red Rider

    Red Rider Well-Known Member

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    That is friggin' nuts that the air cleaner mount covered it. Was that their design, or an installation error?
    newsteve1 likes this.
  2. newsteve1

    newsteve1 New Member

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    I bought it from amazon.

    I have to take some blame because it doesn’t mount up (perfectly) but I figured “what the heck?

    After learning that something was off I headed over to the TC Bros site. The pictures of the mount look very similar, but their images have 4 hole (3 to mount and one for the vent).

    My bracket only has 3 holes. So I either bought a poor knock-off or I have the wrong model/bracket.

    I caused myself a HUGE headache with this.

    The good news:

    I’m working through the tune and I saw 80mph in 3rd last night (this was previously impossible).

    I’ve a 42/190 (lost my 185?) in there.

    Mix screw 2 turns out (stumbles at 1.75 but I can’t get it to stumble as I open the screw).

    Cvp needle.

    Drilled CVP slide.

    Dyna ignition (standard curve VEOS off).

    It’s sloppy in the middle.

    It feels like there is a Big difference between it running warm and hot.

    When it’s HOT (like after 10+ mins of riding) all the issues are minimized (still present, but reduced).

    If I got WOT from 0-80 and don’t let off it runs pretty strong (as it should).

    If I’m in second at @40 mph and try to get on it, it stumbles, stumbles stumbles up to 50 then starts moving...

    I’m gonna leave the jets and replace the slide (with a non-drilled) one today and take some more notes.

    Sooooo f*{%{^}*g pleased that I’m actually working on getting a good tune rather than trying to find a vacuum issue!
    Red Rider likes this.
  3. hotroadking

    hotroadking Super Moderator Staff Member

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    Some things on Amazon are fakes, hard to tell on some of the items.

    You could drill that hole out into the plate you bought to match the port
    and still run that backing plate if you like it otherwise.

    Now you'll be able to get a handle on the CV.
    Red Rider likes this.
  4. newsteve1

    newsteve1 New Member

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    Drilled and done.

    Now the tuning battle. :)
    Red Rider likes this.
  5. newsteve1

    newsteve1 New Member

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    So...

    Mix screw 2 turns out (stumbles) at 1.75
    42 jet

    While riding, it’s strong, but...

    If I go from 1/2 throttle to wide open and try to explore that upper echelon of rpm, it stumbles/sticks.

    If I leave it pinned, it’ll fight through and start screaming.

    If I smash it into second without letting off the gas, I near slip off the back and accurate right on up to 7O+ no problem.

    If I’m riding “normally” (reducing throttle, getting full clutch pulls and allowing the motor to slow between gears) it goes back to step one, fight through the stumble then runs strong.

    Any thoughts on this?

    I’m thinking of trying a needle shim?

    Maybe this is a drilled slide issue?

    When I don’t let off the throttle there is no issue.

    Only when working from low rpm to high.
  6. Spyder

    Spyder New Member

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    When I moved here to east Tennessee from Florida I had to rejet my webber 40 due to being at sea level then to 2800 above. It's a pain in the rump and takes a minute, but finally got the 6 jets right.
  7. Spyder

    Spyder New Member

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  8. Red Rider

    Red Rider Well-Known Member

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    Nice looking ride, Spyder. Glad I don't have a Webber 40mm, I live at 4,000 ft and routinely travel up to 7,500 and down to sea level. My Mikuni 45 non-CV on the 95ci Road King handles it with ease, and even did over Monarch Pass in the Rockies a few times - 11,000ft+ elevation. 2,800 ft shouldn't be a challenge, it isn't even a full millibar of pressure change. Maybe the bike was a bit starved at sea level? With that air box it sure doesn't look like it should have been. Hmmmm, makes me wonder.
    newsteve1 likes this.
  9. newsteve1

    newsteve1 New Member

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    Monarch Pass?!?

    Until last week I lived in Salida. Small world.

    I moved out west and my bike is on a truck somewhere.

    Ultimately I don’t think that altitude is/was my issue, but I’m excited to ride at sea level after only knowing what my bike feels like at 7000+ Im sure it’s gonna pull harder at sea level :)
    Red Rider likes this.
  10. hotroadking

    hotroadking Super Moderator Staff Member

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    I rode my 00 Heritage with a 124 and cv carb from sea level in FL up to 5000 feet in the carolina mountains, never had any lean issues, then again it was probably a bit fat to begin with. Unless the jets were way off to begin with it shouldn't make a difference. Glad you got it worked out.
    Red Rider likes this.

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