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CV carbs rejetting for altitude changes?

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

  1. newsteve1

    newsteve1 New Member

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    never thought of that... was thinking I’d try a compression test.
  2. newsteve1

    newsteve1 New Member

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    087CB6A0-35D6-4C96-9860-E32283B4996F.jpeg The other day I borrowed a compression test kit with the thought “if the valves aren’t seating (or the timing is off) this will let me know.”

    Front and Back cylinders are pretty much identical on 3 tests: cold, hot, hit/wet
    85->90->92 psi respectively.

    I’m still searching for factory specs on compression, but (while this seems low to me), the front and back match. In my mind, I can rule out a valve issue (unless they have the same problem in both cylinders which I find unlinkely).

    It was about 25f outside. I haven’t run it in weeks and it was tough to start (to be expected).

    I ran it without the air cleaner on and ironically, I think those cold temps really helped me a little?

    Almost immediately I could see it spitting air/fuel mix out the carb and it worsened as I blipped it or opened the throttled.

    I don’t know what to make of that.

    Still puzzled.

    Current jets: 42/175
    Needle: cvp

    Also: this is what the plugs look like after about 15-20 mins of riding with this jet setting. They were dry. I don’t think they qualify as “white” from running lean, but wouldn’t mind hearing your opinion.
  3. Red Rider

    Red Rider Well-Known Member

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    They sure don't like like you're running lean, at least from my limited ability to see on screen. Sounds way too much like a vacuum leak or your brand new diaphragm has a tear or is installed poorly.
    I've ridden from sea level to over 11,000ft on the same trip with the40mm CV and CV Performance kit - that ain't the problem. I did have the same symptoms you're having (as best I can tell from your description) and it was a cracked vac line on the carb.

    Let us know what you learn. You may want someone else to take a look, sometimes ya just need a fresh pair of eyes.
    newsteve1 likes this.
  4. newsteve1

    newsteve1 New Member

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    Appreciate that.

    If I knew someone in town or had a local shop, I’d love to have more eyes on it, but you guys are the best I have.

    Vac line is cheap and I only have about 5” of it, so I’ll replace it when I take the compression test kit back.

    I guess I’ll grab a torch and perform the CVP vacuum test protocol around the intake manifold (I bought a new boot and install the carb with a lil Grease).

    I have confidence in the slide diaphragm, but I still have the old one I can swap and test.

    It’s funny (ironic), it had next to zero power wide open in 4th/5th when I first bought it.

    Only After I messed with it (cleaned carb, added/changed jets/needle/float needle and a new air cleaner), did I start experiencing this issue.
  5. hotroadking

    hotroadking Super Moderator Staff Member

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    The first instruction an any service manual is:

    A close visual inspection should reveal the problem,

    These problem appeared after the carb service, so unless
    you did something to another part, it's probably something
    that wasn't done properly during the process.

    So work your way back through the process checking each
    part. The Propane test is a good way to find leaks no smoking though

    Good luck.
  6. newsteve1

    newsteve1 New Member

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    I'm back at it...

    I had a thought when speaking through the issue with a friend.

    My quote was "When get past 3k rpm (or so) it sounds like you've hit a rev limiter in a car... It won't detonate."

    It made think about what needs to happen at that RPM band. On my 97' the VOES needs to be under 4.5 (mbar? psi?) to flip on (or if it's always on it turns off, I can't remember).

    I've bench testest the voes with a vacuum pump and a multimeter. It works.

    Experiment time... I ran the bike with NO VAC LINE (my machine only has one short vac line from the carb to the VOES).

    It ran just as it does with the vac line installed which really leads me to believe I'm unable to get the carb under vacuum and the VOES isn't switching on.

    Stopped by autozone and threw the Vacuum pump on the carb (vac) line. The needle bounced from 5-15ish... If I had a leak, would I get any reading?

    Should the needle on the vac gauge bounce?

    Thoughts (questions):

    - If I've come to the conclusion that I have a vac leak, how do I pinpoint it?

    - It ran better (not great) before I put on the TC bro's (relatively open) air filter with very little resistance. Could I be creating a lean situation because (relative to fuel) I'm just getting too much air?

    - What's your favorite digital ignition? Single or dual fire and do I need to keep the VOES if I get one?

    notes: straight pipes, factory ignition... factory everything. It runs strong (low rpm band) on any jet combo I throw in and the mixture screw NEVER makes it stumble (in or out).
  7. James Powers

    James Powers New Member

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    I found the problem finally. Could never get this thing to level out. Resealed every thing. Changed jetting at least 6 times. Adjusted the idle screw till i bout wore it out. The problem wound up being the diaphragm in the vacuum operated gas shut off. In the Harley fuel shutoff there’s a center spacer that vented to atmosphere so if the diaphragm leaks either gas or vacuum it will go to atmosphere instead of sucking gas into the intake beyond the carburetor. What I found was the center rivet type fastner that’s used in the center of the diaphragms appears to have started loosing up over time and allows gas leakage passed the center rivet to be drawn straight into the cylinders making any attempt to jet the carb to control mixture a futile task. Put a old style off/on fuel shutoff valve in. Plugged the vacuum line at the carb. Jetted the carb to 48 and 195 and idle adjustment I wound up 2 1/2 out and it settled down and runs like a carbureted Harley should now. Wish Harley would stop improving things so trouble shooting things would stay simple. I’m to damn old to keep learning new tricks. Bought me a 82 shovel that I understand
    newsteve1 and Red Rider like this.
  8. newsteve1

    newsteve1 New Member

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    I'm still in low RPM Jail.

    Strong low end, sound like I hit a rev limiter when I start to open the throttle. I have no Tach, but I'd guess it starts between 3-4K. I still ride it around, but I can't break 60mph unless I'm going downhill and uphill SUUUUUCKS.

    Since my last post.

    - I've purchased and tried every combo of Jetting Possible. It runs fine lean, runs fine rich.

    - Went ahead and got an ultima ignition. It runs a little crispier in the bottom (before it craps out) but still craps out. VOES on/off. Zero Difference.

    - Got a torch and tested for vacuum leak. None that I could find; I couldn't make it stumble.

    - Replaced vac line from carb to VOES
    note 1: voes has been previously bench tested and IS operational.
    note 2: Bike runs NO different with VOES vac connected or disconnected.

    - Today I pulled the Air cleaner while it was running, it was warm and in the driveway. Blipped the throttle. I watched the accelerator pump squirt, then witnessed what I would call a "sneeze." It made a "sneezing" sound and mix came OUT the carb instead of going in as the bike stumbled.

    - observation: I think I'm running extra rich with the 48/195 combo. I stink of fuel and my head breathers are wet.

    - Discovered that my fuel tank has a tiny leak at a bracket weld. I'm going to have that repaired and grab the high-flow petcock from CVP.


    Someone mentioned maybe valves/lifters/springs... <-- I want it to be something different, but how would I test for this?? Should I test this?
  9. newsteve1

    newsteve1 New Member

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    And I found this when routing the loom for the ultima ignition... anyone know what this is???

    Attached Files:

  10. hotroadking

    hotroadking Super Moderator Staff Member

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    Looks like an electrical wire where the connection is broken
    newsteve1 likes this.
  11. newsteve1

    newsteve1 New Member

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    @hotroadking - I suppose I deserved that... Any thoughts on the above post??
  12. hotroadking

    hotroadking Super Moderator Staff Member

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    I wasn't trying to be a SA LOL, its hard to see in the image, also can't tell where it's coming from, the end looks different. can you trace it back?
  13. newsteve1

    newsteve1 New Member

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    Black wire. Has a weird "cap" that looks like a small version of (spark) plug wire.

    It's popping out of braided loom that's under the ignition pick up, but it's not part of the ignition loom.

    I'll have to trace it and see if I can find any more details.

    Thoughts on my bike's performance... After much googling last night I'm not convinced that my slide is probably stuck?

    That would explain why it runs well on low end and fuel is not entering the carb/manifold when rapidly opened.

    As it sneezes fuel back when I blip the throttle, I've been reluctant to stick my face in there and see if the slide actually lifts...

    I'll check it out today.
  14. hotroadking

    hotroadking Super Moderator Staff Member

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    I have no clue on the wire,

    Just thinking, was that carb ever subjected to modifications?

    Lots of people thought they could get more performance by drilling out the hole in the bottom of the slide and putting in a lighter spring, most of the time this ended up screwing up the slide movement, it would bounce or come up to quickly, making drive ability poor. If this was done to the carb your only option is a new slide and stock spring.

    Basically the only things you should have to do to a cv in order to have good driveability and power is needle position, jets and idle mix screw.

    Those plugs look bad, either you have oil burning or it's dumping fuel, so clean them up, or get some new plugs for it.

    Since idle improved with the AC off, means you are rich, you just added air.

    The Idle mix screw is the key to knowing if you are rich or lean. Click here
    to get the steps.

    https://cv-performance.com/harley_mixture_screw_tuning

    Once you get the mix screw/pilot jet sized correctly then worry about
    the main jet and the needle.

    The needle is going to be your key to mid range power, mpg, and eventually
    total wot power. leave the main jet alone for now and work on one circuit at a time starting with the idle mix setting, then adjust the pilot jet and readjust the idle mix until you get it right.

    Hope that helps.
  15. newsteve1

    newsteve1 New Member

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    Ahhhhemmm... I .... uh... got a brand new slide and drilled it out... I’ll get a new one :(

    Live and learn.

    Do you feel I can eliminate the idea of valve/lifter/spring issues?

    My thought is that they are fine because the bike runs so strong at low RPM and compression is consistent across both cylinders.

    The thought lingers because how else would fuel come OUT of a carb?
    ______________________

    Note: I inspected slide yesterday. It moves fluidly when I open it with my fingers. Vacuum noise present, moves with “ease.”

    I can’t imagine air moving it, I just seems too tough (cvp spring installed).

    Last: I pulled the cap and the slide. I noticed a little char (burn mark) on the top of the slide that appears to be coming from the choke/enricher port.

    Does that suggest anything?

    I have the replaced the choke cable with a shorty and have the cvp cap mount bracket (which I love because fishing that choke through to the horn suuuucks).
    __________________________

    Plan of action:

    1) replace slide with new cvp slide/needle/spring and clean carb. (I’m gonna try some pipe cleaners to make sure I don’t have blocked passages).

    2) install jets 42/180, mix screw at 2.5 out (42/180 <— arbitrary starting point).

    3) bring idle as low as possible (no tach)

    4) follow mix adjustment instructions.

    5) rejet/repeat if needed.

    6) install new plugs and examine after hours/miles to confirm proper mixture.

    7) hope that I can open this thing Up because cruising around at low RPM sucks.
  16. hotroadking

    hotroadking Super Moderator Staff Member

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    did you drill it out larger or just clean up the hole and not resize.

    It's the resize that causes the problem, making sure any casting burrs are out
    is ok as long as it doesn't make the hole larger.

    The slide moves with air pressure, the more the engine demands the higher the slide will move, its not like a Mikuni where the slide is mechanical. and yours must be working to some extent as you can ride the bike and increase rpm/speed.

    If you take the slide out be careful with the diaphragm they can tear and that's a problem with slide functioning as well, if it's torn the slide won't move, if its not properly installed and sealing, the slide won't move, it's a Constant Velocity (CV) carb, velocity and pressure are the keys to a good working CV.

    Do you know someone with a spare CV sitting around, if so borrow it, hook it up and see what happens.

    As to it spitting back fuel, timing, cam timing, exhaust with or without baffles combined with some cams can cause reversion (popping in the exhaust) where the exhaust valve is open during the suck stroke of the pistons and pulling unburnt fuel back into a hot combustion chamber and it fires, this is generally seen on open pipes with bigger cams as you let off the throttle slowing down..
  17. newsteve1

    newsteve1 New Member

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    I opened up the vac hole. I got all excited about making the bike run hot and fast... saw that as a common mod and jumped on the band wagon...

    I just static/dynamic timed the bike with new digital ignition so I feel good about that.

    I can get the throttle open further in a roll vs a blip.

    When blipped/it sneezes and I can SEE mix exit the carb instead of enter.

    I don’t think the cam has been changed but it does have straight pipes.

    No pops and back fires... just can’t get it to suck fuel in like it’s supposed to...

    I have the OE slide. It’s not ripped/damaged... I’ll throw it in.
  18. hotroadking

    hotroadking Super Moderator Staff Member

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    Won't hurt to try it other than some labor.

    Also be careful turning in the idle mix screw, don't jam it down
    let it lightly seat, otherwise you can fubar the hole the mix screw is
    using, making it larger and impossible to tune.

    Turn it in, lightly seat, turn out 3 turns and stop.

    Warm it up, set the idle at 1500 to 1800 rpm with the
    throttle lock.

    Turn the screw in lightly, at some point idle should change.
    stop, turn the screw out lightly, the idle will go back then
    at some point change again. Count the turns, so you can find the middle point.

    The mid point between the two points where idle changes is your setting.

    When you find center, turn it off and turn the
    screw in counting turns it should be 2.5 from the bottom (2.7 or 2.4) is close enough.

    If it goes all the way in and the idle doesn't stumble or change
    your idle jet is too large, you want to be 2.5 turns out.
  19. newsteve1

    newsteve1 New Member

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    What’s this hole in the upper left for?

    My TC bros AC mount covers it.

    Is that okay? A2DF3ADD-D62A-40BD-9A3C-4DAF01BC5532.jpeg
  20. newsteve1

    newsteve1 New Member

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    Turns out it’s a vent for the float/bowl compartment and it shouldn’t be sealed up.

    The BIG issue has been solved, now on to jetting/tuning.

    I’m so happy finally figured this out.

    “Close visual inspection” for the win.
    Red Rider likes this.

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