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Thread: CV Carb rebuild

  1. #1
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    Default CV Carb rebuild

    Hello you beautiful bastards,


    Rebuilding a CV carb for my 2003 sportster. Ended up having a crack in the casting so got a used one off ebay for parts.

    Carb is all back together and starts, idles, accelerates and most important, doesnt leak.


    HOWEVER,

    Tuning is turning into an issue because I am running very rich, Black smoke during idle, fire when accelerating, but no backfiring.


    I have the mixture screw just barely cracked from the seated position, no more room except to seat it, which cuts gas on acceleration.





    Here are the specs:

    Old carb was set for drag pipes and that stock sportster air filter

    Main jet: 180
    Slow jet: 42
    Stock needle and slide


    Since rebuild still running drag pipes but have one of those cute small air cleaners now (all new jets and tubes and gaskets, plus good cleaning:
    Main jet: 170 (tried the 180 but was too rich, same problem as above but would stall on acceleration)
    Slow jet: 42 (tried a 45 but had to fight it for the 1/4 throttle turn to keep from stalling)
    Needle came from a kit that insisted i drill a little bit into the slide as well, still have a stock needle and slide on hand



    Accelerates and idles fine but bellows black smoke on idle and fire on acceleration. I have no where left to go with mixture screw to reduce gas flow


    Should I put back on stock slide and needle?

    Should I go down a size in slow and main jets? if so what do you think? got a slew of main jets, but will have to pick up a slow jet

  2. #2
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    Ya might want to clean up the float needle and seat ...
    Check the float level too ...

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    How does it run without the cute small air cleaner? Always backtrack to last successful setup.

    Post pic of cute small carb strangler.

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    In addition to the above, check that the choke cable is allowing the enrichener plunger to fully seat.

    A slide diaphragm with a hole in it, no matter how small, will make a CV run bad.

    Jim

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    Didnt think about float setting procedure, the new one i put in looked about the same but i guess ill have to get some wood and try to go through the procedures. I actually threw the old float needle and same result, thought it was too the old body that i tossed due to the crack in casting. Since I did nothing but through on a new float, it will probably be this

    Air clean was put on last year with the old set up, performance approx the same. Its one of those TC bro small air cleaners.


    This choke cable has some rough spots too it so maybe ill pick up another one of those while im at it.

    Very appreciative gentlmen. Guess im riding a honda for a few days

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    Update

    Dropped the carb off at HD this morning as my eyeballing the float tab wasn't going so well. $25 later i have my carb back.

    Running worse than before. Ive gotta choke the shit out of it to start and idle. Mixture screw barely cracked and still shooting smoke (although maybe a bit better than before). A light twist of the throttle will stall the bike. Again mixture screw barely cracked passed seated.

    I guess I need to go to like a 40 or 39 slow jet and a 165 or 160 main jet?

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    You need to start over. The CV is dead simple and should run OK with almost any combination of stock jets. (Not run well, but crank, idle, and go down the road.) Your idle mixture screw should be 2 to 3 turns out, and if the timing is right, the motor will idle just fine. If not, you need to start over. The float level is dead simple as well, lean the carb over until the needle hits the seat, but the spring plunger in the needle is NOT compressed, and the seam on the float should be parallel to the bowl gasket surface.

    I know you may be pulling your hair out and/ or drinking at this point, but you will get it, and learn in the bargain.

    Good luck,
    Jim

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    Thanks. I took your advice and sure as shit one of my shims fell off in the slide and was in there side ways holding it up higher than it should have been.

    No longer running rich and idles fine.

    Yall the best.

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    Excellent!

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    Quote Originally Posted by tomiles View Post
    Thanks. I took your advice and sure as shit one of my shims fell off in the slide and was in there side ways holding it up higher than it should have been.

    No longer running rich and idles fine.

    Yall the best.
    So, I gotta ask, he charged you 25 bucks and they didn’t notice the side ways shim n the slide?

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    No, I specifically told them I had everything done and just needed the bowl adjusted to spec. That being the case they charged me like 15 minutes in labor while i waited in the lobby.

    Our damn pride some times... Didn't want to seem like a chump to the service manager so I had to sound macho and tell him I did everything else perfect except that the float was needing to be set. They had to reason to do in a full inspection because I proclaimed all i needed was the bowl adjustment to spec...

    Im at the point in my motorcycle tooling that I can talk the talk, but not quite the walk, but im crawling lol

    Thats the fun of these things... and the magic of this forum
    Last edited by tomiles; 09-15-2019 at 9:49 AM.

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    "I have the mixture screw just barely cracked from the seated position, no more room except to seat it, which cuts gas on acceleration."

    Not sure what you are talking about. The mixture screw has to be out a couple of turns or so.
    If the mixture screw is barely cracked open, I am surprised it runs at all!

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    While we're on this, I am near the point of addressing the stock CV on my upgrade from 883cc to 1250cc.
    Just waiting on a set of jets in the mail before I get the carb apart.

    The bike started as an 883 Hugger 2003 Anniversary, that has been ratted out to a trike for my old lady, and needs to be more of a tractor.

    What has been done:
    1250cc big bore kit from NRHS.
    "N" grind Andrews cams installed with new lifters from NRHS.
    New shorty exhaust mufflers, w/baffles lined inside, and the stock pipes have the crossover eliminated and welded shut.
    I used the stock 883 heads from the bike as NHRS said would work just fine.
    I also have an Arlen Ness "Big Sucker" stage one intake air cleaner for once carb is on.
    The ignition module upgrade to a Dyna 2000i set up for a single fire with the correct Drag Specialties coil, the whole kit put together by Dan from NRHS for me. curve 2, voes normal, 6500 rpm, single fire on the digital switch set.

    The literature from Andrews mentions about the stock CV carb to go up 3 or 4 slow jet sizes, remove 1/2 to 1 full coil on the slide spring, and to add a .030" shim under the needle.
    I haven't done anything with the carb yet.

    I plan on using Andrews Cams carburetor suggestion, does it sound like I am on the right path, or am I missing something?

    I appreciate y'alls knowledge and thanks in advance.

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    On all of these slide type carbs, the NEEDLE is the thing! A shim under the needle will crudely enrichen the mix pretty much across the board, but that may not give you the ideal fuel curve.

    I like the Keihin tuning kits, sold by several suppliers, as these kits contain genuine Keihin jets and needle, and are of much better quality than aftermarket kits. I would buy one for a 1200 XL, and use the enclosed needle, as well as the larger intermediate and main jets as a starting point. I would not trim the spring or drill the air vent in the slide. Your idle mixture screw should be 2 1/2 to 4 turns out with this combo, and the off-idle response is trimmed with that adjustment. Shims, if any, under the needle would be a final mixture adjustment.

    You did not mention which cams you have, "N" just denotes a late evo XL gear set. N4, N6? Not that it really matters for your baseline.

    Be sure of your ignition timing before starting in on the carb tuning, and selecting different curves in the box will go hand in hand with carb tuning.

    If you have not done this before, you are in for a steep learning curve. Start rich, and work toward lean, it's safer for the motor.

    Good luck,
    Jim

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    and the stock pipes have the crossover eliminated and welded shut.
    That crossover greatly assists midrange torque. (It's a very old car trick.) Removing it turns the stock downpipes into engine-strangling drag pipes. Since you spent all that money on horsepower, I'd get what you paid for an find a stock crossover setup. A lot of stuff done for cosmetics is anti-functional.

    Headers are nice too but they don't sound like a Harley and cost a lot more than a crossover someone removed to look cool. I collect those from my bros shop so I have a reserve.

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    Quote Originally Posted by farmall View Post
    That crossover greatly assists midrange torque. (It's a very old car trick.) Removing it turns the stock downpipes into engine-strangling drag pipes. Since you spent all that money on horsepower, I'd get what you paid for an find a stock crossover setup. A lot of stuff done for cosmetics is anti-functional.

    Headers are nice too but they don't sound like a Harley and cost a lot more than a crossover someone removed to look cool. I collect those from my bros shop so I have a reserve.
    I did not know about robbing the engine of torque.
    A good while back, the old gal was complaining of the heat on her leg, so I removed it and closed it up.
    It seemed like it would be okay because of so many true separate duals I see people running, speaking Harley's I see.

    Once I get through the carburetor, cleaning it, seeing what jets are in there, my rebuild kit is on the way, no plans to cut the spring now (on Jim's advice), and never did think about drilling anything, then trying to tune it, I will look into another set of pipes since I sabotaged some midrange.

    Thanks for the knowledge tip, and Merry Christmas to y'all.
    Rusty

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    It seemed like it would be okay because of so many true separate duals I see people running, speaking Harley's I see.
    Most HD exhausts are chosen for looks and sound. You could wrap the crossover then install a heat shield for both appearance and keeping the leg off the wrap.

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    Quote Originally Posted by farmall View Post
    Most HD exhausts are chosen for looks and sound. You could wrap the crossover then install a heat shield for both appearance and keeping the leg off the wrap.
    As is most things on a HD or any bike that has been modified! I tell people look at a High Performance car do you see separate pipes, or a collector type system for the exhaust, of course except nitro burners where there is no need for low RPM performance.

  19. #19

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    I wouldn't use any of the early CV carbs with the sloppy fitting carb float needle pin. The pin eventually eggs the 2 holes that it slides thru and the float gets cockeyed causing the needle to drip gas into the cylinders . After a while the gas dilutes the engine oil to the point of blowing/smoking past the piston rings. I worked the parts counter in a HD Dealership and we had a customer with a 1990 Fatboy that started smoking about 800 to 1000 miles after he changed his oil. Oil/gas slime was also running out of his air cleaner so bad he ran a hose from the AC breather bottom fitting out past the back fender. About 1994 or so HD changed the CV float pin to a slight to medium press fit and that stopped the problem. If you buy a CV carb at a swap meet bring a proper fitting philips screwdriver and drop the float bowl. Check to see if float pin is sloppy in its holes. Pass if it is. Usually it takes 20,000 miles or so for engine vibration to egg the aluminum float pin holes. Some guys sharpen an awl to a needle point and lightly smack next to the float pin mounting hole to make the pin a press fit in the hole. You have to support the stripped carb on a piece of lead when you smack it as the pin holes are located in two aluminum towers and they are ez to snap off. it works for a while but usually the problem reappears. The carb can't be easily repaired/tuned and I would just look for a later model CV carb.

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