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CV carbs rejetting for altitude changes?

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

  1. James Powers

    James Powers New Member

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    I have a 2003 flhtc carbrurated. I relocated from Fairbanks Ak elevation 600’ above sea level to Albuquerque NM alt. 5000’ above sea level. Shipped it here and when it got hear i ask the local Harley shop to rejet the carb for the altitude change and was told that because it had a CV carb on it that no jet changes were nessacary because the CV carb adjusted to the altitude automatically ? That sound right to you? I have since installed CVPreformance kits and rejetted it and am very happy with how it runs but I’ve always been curious about the altitude compensating cv carb and if that information is correct?
  2. hotroadking

    hotroadking Super Moderator Staff Member

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    CV carbs have floating slides that adjust height based on demand of the engine
    so to some extent that's correct, you may have to adjust the idle mix screw a bit
    to get the best idle depending on where you had it set in AK...

    If it's running good and getting good mileage then you probably are ok.
    Red Rider likes this.
  3. newsteve1

    newsteve1 New Member

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    What CV performance jets did you use?

    I'm at 7000 ft in CO with a 97 sporty 1200. I just picked it up.

    Put in the 180 and the 45 (for "stage 1" straight pipes and an intake).

    1st and 2nd gear are great, but when I try to open in third + I'm at a total loss. It bogs (feels like I'm hitting a rev limiter in a car).

    Going well, but need some help. Based on what I've read, maybe I need to bring the main jet down to 175?

    Thoughts??
  4. hotroadking

    hotroadking Super Moderator Staff Member

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    main jets are used when you go WFO, the needle controls the fuel in the mid range as it comes up the tube from the main.

    Key is the pilot jet, turn the idle mix screw in until it bottoms (GENTLY DO NOT FORCE IT) counting the turns, then, turn it out 2 and a half turns,

    Fire up the engine get it warm, lock the throttle open at 1500 to 1800 rpm

    Turn in the screw until the engine stumbles, counting the turns, then, reverse that counting turns out until it stumbles again then set it half way between the low stumble (turn in) and high stumble (Turn out)

    Turn off the engine, turn in the screw and count the turns, it should be around 2.5 turns if it's spot on, if it's less the pilot jet is too large, if it's much higher like 3.5 the pilot jet is too small.
    newsteve1 likes this.
  5. newsteve1

    newsteve1 New Member

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    I pulled the carb (again) because my float is getting stuck. No evidence of anything so hopefully a new fuel line/filter will do the trick :(

    My sweet spot for the mix is right at 2 turns out.

    Think I should replace the 45 pilot with a 44 upon reassembly?

    at 3/4 throttle and up, I have nothing. I can't call it rich. I can't call it lean. It just sucks. Feels like the whole bike chokes and I get nothing.

    Fun notes: Prior to installing the CV performance tuners kit and jets the carb had a 185 main in it... I actually reduced it to a 180 (it doesn't mean much to me because the bike ran like crap).
  6. hotroadking

    hotroadking Super Moderator Staff Member

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    float might not be set properly be sure it's position is correct

    Since you have the carb apart, lean out the pilot jet one or two sizes
    I would go two.

    Where is the needle, do you have it shimmed?

    I'd say you are rich, thats what the bogging is from, too much fuel
    drop the needle if you have it shimmed remove a couple, smaller
    main jet, smaller pilot,
  7. newsteve1

    newsteve1 New Member

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    I spent lots of time on the float. Made 15 degree platform and set properly. Pretty confident in it and bench test it.

    Pilot: I think I only have one size leaner, I’ll try it.

    Needle: assuming you mean the slide needle (terminology?), it’s not shimmed. I bought a cv performance tuners kit and a slide. Using both those in this application (with no modification).

    Note: when I pulled the main jet I also replaced the immulsion tube (cvp kit). I didn’t not see a nozzle come out, but I’m assuming the nozzle is what I see protruding inside the carb?

    Attached Files:

  8. kenfuzed

    kenfuzed Administrator Staff Member

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    Hi Steve, the pilot jet size won't apply to the problem you described since it only supplies fuel at idle. The needle takes over just off idle (with help of the mixture srew) and works all the way up to just above 3/4 throttle. At full throttle the slide lifts the needle open and the main jet delivers all fuel requirements. What you have described could be one of the following:
    1) Sticking slide or bad slide diaphragm.
    2) Vacuum leak at the manifold (manifold to heads or between carb and manifold). This is the most common.
    3)Debris clogged in the inner passages.
    4) Sticking float needle valve.
    5) Restriction from the tank, which could include a) clogged petcock, b) bad gas cap vent.
    6) Needle jet (stainless steel nozzle) on top of emulsion tube is upside down or missing.
    7) Problem with ignition module cutting out.

    Typically if you were too rich up top (main jet) you would be able to tell by fouled plugs or heavy gas smell from the exhaust. It would bog but not necessarily cut out as mentioned, which tells me the problem is something other than jetting.
  9. newsteve1

    newsteve1 New Member

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    @kenfuzed @hotroadking - appreciate all the help!

    1) Sticking slide or bad slide diaphragm. (Brand new, moves smoothly)

    2) Vacuum leak at the manifold (manifold to heads or between carb and manifold). This is the most common. (I'll inspect, and use a little grease when I reinstall carb)

    3)Debris clogged in the inner passages. (will blast with carb cleaner (Again). also installing new inline fuel filter)

    4) Sticking float needle valve. (Yes. I don't know why, but I have overflow issues. I've carefully adjusted float and replaced needle. Seat is clean, passages (seem) clear. bench tested, functioning)

    5) Restriction from the tank, which could include a) clogged petcock, b) bad gas cap vent. (Petcock *seems* good and carb often overflows. Installing new fuel line, have brand new gas cap - kuryakyn 8669 stock style vented cap)

    6) Needle jet (stainless steel nozzle) on top of emulsion tube is upside down or missing.
    (You can see the nozzle in the picture above (correct)? the CVP kit does not come with a new one, so I left it in)

    7) Problem with ignition module cutting out. (This very well could be, but before I started messing the carb, there were no missfires or really unusual circumstances at wide open, the bike was just sluggish as can be.. An obscene amount of gear dropping on hills to try to salvage any power. Since it has pipes and frankensteined intake (stacked gaskets, cut filter and terrible seals all around), I figured a carb rebuild with jet-kit would be a great place to start. I've also installed a tc bros (open air filter). I'm wondering if this was a good idea now that i have exhuast/head breathers firing off into the air).

    My intentions:

    1) Clean passages in carb (again).
    2) Leave 180/45 combo (stage 1)
    3) Inspect/clean manifold
    4) Lightly grease manifold boot upon reassembly (I haven't done this yet).
    5) Install new fuel line + inline filter
    6) Adjust mixture per @hotroadking 's suggestions
    7) Pray that the *&^% float doesn't stick.
    8) Circle back and let you guys know if I've found success or I'm back the drawing board.

    Again, Thank you for sharing, your knowledge is invaluable. I hope my issue helps others in the community.
  10. hotroadking

    hotroadking Super Moderator Staff Member

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    Good tips. If you have a stick petcock make sure the vac line is good. If it’s older replace it. Cheap at any parts store




    Sent from my iPhone using Tapatalk
  11. newsteve1

    newsteve1 New Member

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    There is no vac line on the petcock. After I get it running right i’d Like to do high flow fuel stuff.

    I can’t find what the one vac line on the carb does, and/or what it’s connected too? Some sorta solenoid?

    Update. Noticed the float needle seat (walls) were muddied up. Used some q tips and a lil gentle pumice polish to clean/smooth it out, then flushed it was gas to do my best to keep abrasive from staying in the carb.

    Float jet seems to be operational, but I’ll find out more tomorrow when I fire it up.
  12. hotroadking

    hotroadking Super Moderator Staff Member

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    the vac line on the carb should run to the fuel petcock.
  13. newsteve1

    newsteve1 New Member

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    Well. Finally got to throw a leg over and test.

    1) ez mix screw has 0 impact.
    2) 3/4 throttle fail exists still (video attached).
    3) running 175/45 main/pilot
    4) idles well
    5) cleaned 2x (though a read a good thread on cleaning the passages).
    6) I think (this could be my brain) I smells rich. Can’t confirm.

    Thoughts.

    I’m going to install the factory mixture screw and experiment.

    Greased intake boot (no manifold blockage).

    Vacuum line from carb goes to some sort of solenoid?? (No factory petcock).

    Video: the forum won’t allow me to attach a video or link.
  14. newsteve1

    newsteve1 New Member

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    Update:

    1) I pulled air filter and noticed fuel around bottom lip (rich indication right?)

    2) replaced ez mix with factory screw. (Pulled air filter to ensure I could see needled tip : and I could).

    3) bike won’t stall with screw all the way in. Bike won’t stall with screw 5+ turns out.

    Running too rich with a 175 main???

    Confused.
    Last edited: Oct 13, 2018
  15. newsteve1

    newsteve1 New Member

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    Started researching VOES.

    Since I bought it, the bike was never strong wide open.

    Carb kit has not improved much (more steady idle).

    Before I dig into the ignition to see what’s going on, does anyone think this complete lack of top-end power could be the result of bad(mid-adjusted) VOES?

    Sounds like it would kill top-end power, but it doesn’t explain my rich situation.

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