Rebuilding a Keihin CV40 carb - Harley Davidson Forums: Harley Davidson Motorcycle Forum

**Dave63** · 03-27-2012, 12:05 PM

Rebuilding your CV40 carb isn't rocket science. It's simply a matter of taking the carb apart, cleaning items that are prone to poor performance if exposed to dirt for decades and rejetting it properly upon reassembly. Float adjustment only has to be set of it's messed with, you hit the float and bend the tab, or the platic float develops a leak and becomes heavy. One other reason would be is if the needle were bad and needed to be replaced, and in this case, that happened. Start with your typical, CV40 carb. The Keihin CV40 was introduced in 1988 on the XL models, however did not originally have an accelerator pump. 1989 to 2006 models did. This is your typical CV40 carb. This model is a 1992. (Special thanks to LilJo!!)

Tools needed will be:

1.) Medium straight blade screwdriver
2.) Medium phillips screwdriver
3.) Small straight blade screw driver
4.) 8mm wrench
5.) pick
6.) can carb cleaner (2+2 is my favorite flavor)
7.) Thread lock red (For fuel elbow replacement only.)
8.) 9/16" wrench
9.) fuel elbow removal tool, or a vice, if replacing the fuel elbow.

When you take the bowl off, you'll see the flat, main jet, pilot jet and needle in place. The seam of the float should be about level with the side of the carb casting, or just a tad below it.

NOTE ARROW AT LEFT OF LEFT FLOAT PIN TOWER. YOU NEED TO PRESS THE PIN TO THE RIGHT. IF NOT, YOU'LL BREAK THE TOWER, AND THE CARB IS JUNK!! You can just see the little arrow, pointing to the right, cast into the carb body.

Remove your jets using a good screwdriver, and the appropriate size. If not, you can strip them (Brass is soft) and then you have issues.

Not the larger one is the MAIN JET still screwed into the EMULSION TUBE. The smaller jet is your PILOT JET.

**Dave63** · 03-27-2012, 12:10 PM

Disassemble your carb, piece by piece, laying your parts out on a clean, open working area. If you lay them out in the order they cam off the carb, you'll have no issues with putting them back in, in the correct order.

Once done, you'll have a smaller carb body, that needs to be thoroughly cleaned, insode and out, making sure to pass air through all the air bleeds and ports. Remove everyting, including the main jet, pilot jet, emulsion tube (main jet scews into it) and the diaphram and associated parts.

Clean the body and bowl with carb cleaner and a tooth brush. I use a series of brass and mild steel brushes. Afterwards, I have a polishing process I developed, that's fast and efficient, making the carb look like new again.

**Dave63** · 03-27-2012, 12:16 PM

One thing you may want to do, is to remove the air fuel mixture screw, and clean and inspect the tip. In the screw passage, there's a brass needle screw, a spring, an o-ring and a washer. Note the order they came out in. Note if there's any damage to the screw as it's thin and fragile. Clean screw and replace all removed parts in the order they were removed. Kits for rebuilding will come with a new o-ring. Replace it if removed.

Remove the "choke" cable. It is removed by turning the plastic 9/16" nut that threads into the carb body. The brass pintle on the end is what is moved within the passage when you pull the knob, with the thin needle end allowing more fuel to enter the carb, and the wider brass part allowing for more air. That's why this isn't a "choke", rather an ENRICHENER. It adds fuel, not cuts off air the supply (butterfly) making the mixture richer.

Make sure to clean the enrichener port out well with carb cleaner, and clean the pintle well, also.

**Dave63** · 03-27-2012, 12:26 PM

Once the carb body and bowl are cleaned and polished, and the carb throat is polished, I'm ready to reassemble. In the case of this carb, the fuel inlet was plastic. This needs to be replaced. The old elbow id removed and a CV-Performance brass elbow is put in its place. Refer to the STICKY on elbow replacement.

The accelerator pump 3-screw cover is removed and the diaphram is inspected. Keep in mind that the diaphram can delaminate and peel apart. If you see this, regardless of being only one side, then replace it. There's a small o-ring in between the cover and the carb bowl that needs to be replaced when removed. In this case, I also replaced the hardware.

The emulsion tube, main jet, pilot jet, needle and float are replaced. Keep in mind, when removing the float pin, THE PIN IS REMOVED FROM THE LEFT TO THE RIGHT, IF THE PIN TOWERS ARE FACING YOU AND THE FLOAT IS FACING AWAY FROM YOU. If you try to force it the other way, you'll break a tower and the carb is now JUNK. There's an ARROW pointing towards the way the pin is to be removed.

Once all parts are installed, replace the bowl, accel pump bellows, accel pump actuator shaft and 4 screws.

**Dave63** · 03-27-2012, 12:31 PM

Replace the slide and diaphram. I polish the slide, and bevel the leading edge for better air flow. Make sure on reinstall, the lip of the diaphram fits into the upper housing groove, or you'll tear it and it'll leak. It's a $60 part. Keep that in mind. As the cover is placed on it, you can push the rubber end back into the groove with a small screwdriver. As the lip seats, you'll see the cover meet the carb housing.

**Dave63** · 03-27-2012, 12:41 PM

Install your main jet needle, the spring seat and the spring. I used an XL needle for this build as it works well with giving good midrange fuel with no bog. If your engine is stock, install the needle (XL PT# 27094-88). FOr larger engines. cammed engines, I use a .050" shim under the needle to add just a touch more fuel.

Can be seen in throat, into main housing:

You can either install a DynoJet spring which is shorter and a lighter spring rate, (8.8 onces for 3" compression and 5" long VS stock which is 12.5 onces for 3" compression and 5.5" long) a stock spring, or take a stock spring, cut off 3 rings from it, and your slide will react faster, giving similar results as the DynoJet spring.

Now that all your parts are inside the top of the carb, the cover can go back on, sa can the right side cable cradle.

**Dave63** · 03-27-2012, 12:46 PM

Install your chokepintle and spring back on the cable, and reinstall back on the carb. GENTLY tighten the plastic nut back into the carb housing.

I generally set the air/fuel screw 2 turns out to start. This carb is set up for a Big Twin, with a 190 main, an XL needle shimmed .050", a 48 Pilot jet, new accel pump diaphram and a stock diaphram spring, and no drilled slide air-bleed hole.

This is your completed carb:

LilJo · 03-27-2012, 12:57 PM

OUTSTANDING, Dave!

Now I'm REALLY glad you got that carb. Well documented, this ought to help a lot of people out. Thanks for posting, man.

A LOT of gasoline has gone through that carb. And now it looks better than new.