Keihin carb question

Discussion in 'Engine, Fuel and Exhaust' started by marbleharley, Sep 24, 2008.

  1. marbleharley

    marbleharley New Member


    I have a 1993 Fatboy that I'm slowly putting together. Along the way I was given a Keihin carb from a 1994 FXR. The trouble is I don't much about the carb and I'm not getting a response from Keihin. The most I can see is the part number or serial number on the side of the car (PA40BBF23) I assume it's CV with the float on the bottom but that's it.

    Any help history, size, fixed jetting etc would be helpful

    Thanks in advance,

  2. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator


    After you do what Hobbit says and make sure it will fit your bike (bet it is a CV40, but may be a CV44!), get a "rebuild kit" (you will be surprised!) and completely dissassemble and clean everything carefully. Be careful getting too aggressive with spray carb cleaner since you don't want to blow any of the little bits out of sight. A good aromatic liquid solvent will do nicely with some Q-tips and an old toothbrush. Watch out for the "rubber" parts and the solvent though. Will probably swell them.

    Decide what you want to try for jets, and replace the ones in the body if they look bad. Also, while you have the carb handy, turn the body over and find a spot on the bottom that looks like it should be a hole, but has some plastic filler sealing it (probably red or brown colored). If this is not there, but you see a small screw head in a recessed hole, great! This is your idle-air mixture screw/needle. If the plastic IS still there, drill it out carefully to expose the screw. You will probably want to fiddle with that once you have the bike running. (See photo)

    I would also suggest that you replace the accelerator pump. Chances are that has never been done, and it will be itchin' to fail on you. Finally, look carefully at the slide diaphram to see if that looks old and worn. If so, replace it. OEM is fine, but if you want the Dynojet Thunder Slide, get after it! There are some that would suggest you drill out the hole in the top of the slider to 1/8". DON'T. It is easy to mess this up, and then your throttle response will be crappy.

    I like this carb. It is very simple and easy to mess with. Once you get the bike back on the road, you can easily rejet based on the way you ride and what you want the bike to do. You can spend lots of money on some of the aftermarket models, but once you have this carb working, it does what it is supposed to. The only other thing you might consider is putting in a Yost Power Tube. Does a better job of atomizing the gas, and they include a bunch of jets in the kit. Again though, DON'T drill out the port in the slide!! Just MHO.

    Let us know how you fair.


    Attached Files:

    Last edited: Oct 2, 2008
  3. vnamvet

    vnamvet Member

    The main jet was 1.70 (Part # 27115-88) in the main and used a 42 (part # 27171-89)for the slow speed jet. I have had three FXRs, BTW and miss every one of them dearly!

    As TQ stated above, access the air mixture screw by drilling out the aluminum "plug" found on the back side behind the float bowl. Drill a 1/8" small hole, screw a sheet metal screw into the hole about 3-4 turns and pop out the plug with a "sideways" motion!
    2 1/2 to 2 3/4 turns out from fully seated should put you in the ballpark. make sure the engine is warm and the bike is off the jiffy stand and bike is upright!

    A 45 slow speed jet (27170-89) and a 170 (hd part#27115-88) or 175 (hd part #27090-89) main with a high flow air cleaner would be ok too.

    Stay away from a THUNDERSLIDE kit..............harley jets will not fit when you need additional jets (thread size is different).

    The accelerator pump diaphram (27361-76A)is a definite.....replace! While you're there, replace the plastic fuel inlet with the newer version (27371-76A) which is not prone to cracking with heat!

    Finally, I have used the YOST power tube with good luck!