• Don't overlook our Welcome Package, it contains many links to important and helpful information about functions at VHT like posting pictures and sending PMs (private messages), as well as finding the parts you need.

    AD

How to Rebuild the VB Carburetors

LongDistanceRider

Administrator
Staff member
Joined
May 22, 2020
Total Posts
11,344
Total likes
930
Location
Vancouver, Washington USA
This is dealing with the VB22J carbs in particular but most of it applies to the VB21 and VB24 carbs. As everyone knows that has done these they are problematic to get right the first time at best so hopefully this will help you get there. In this case I'm dealing with VB22J carbs that have had previous attempts to rebuild and get right to no avail.

Tools/equipment needed: 7mm wrench for the jet holder, 8mm wrench for the left carb linkage and the sync screw locknut, impact driver to remove the screws with a #2 and #3 Philips tip, variety of screwdrivers that need to be filed and modified to fit, Allen wrenches that fit the new Allen screws you need to buy to replace every screw, 400, 600, 800 grit sandpaper, spray carb cleaner, jet gauge(optional), number drills #60 thru #80 available at RC car shops and some misc. stuff you already have laying around.
Stainless Steel Allen Head Screws: 8: 4x12mm, 8: 4x16mm, 4: 5x12mm, 5: 5x16mm, 4: 6x14mm

Carb Kits: I recommend getting the Honda OEM kit since it has the correct and latest materials as well as a couple of parts not supplied by the aftermarket. They do not include jets, float needles or air cut valves. Aftermarket kits include jets which unless damaged never need replacement and are for the most part the wrong sizes. Use those jets at your own risk knowing that you will likely be putting the originals back in.
Float Valves/Needles: For the VB22 carbs I strongly suggest the Honda OEM ones since they are the correct length. VB21 and early VB24 carbs with Black floats can use aftermarket float needles.
Aftermarket kits include float valves that may not be correct and the jets that never wear or need replacement.
 
Disassembly and Cleaning

First and foremost is to take pictures as you disassemble them in case you lose track of what goes where.
201_4642.jpg 201_4643.jpg 201_4644 (1).jpg 201_4645.jpg
201_4646.jpg 201_4647 (1).jpg 201_4648.jpg 201_4649 (1).jpg 201_4650.jpg

One thing to check while disassembling is the float height
201_4663.jpg 201_4664.jpg

As you can see neither float level was correct due to float needles and 1 float pin having been replaced with a nail
201_4684.jpg
 
Last edited:
More Disassembly and Cleaning

Separate the carbs by removing the 2 steel bars and pull them apart being careful not to lose the spring separating the throttle shafts. An Impact driver with a #3 Philips tip works well on the screws and you'll be replacing them with SS Allen heads. Now strip them completely including all of the jets. There is one jet, the primary emulsion tube, that is under the Primary main jet
201_4693-001.jpg
that will require you to make a screwdriver that fits the passage. It's a @4mm hole.
NOTE: in making screwdrivers to fit the jets you want the tip to be even across and also file/grind the end of the blade so there is no taper in it. The thickness of the tip should be 1mm to fit the slot of the jet properly
Soak/submerge them for 8-12 hours in your favorite carb cleaner unless the instructions for it say otherwise. READ the instructions. I use Pine-Sol which has to be flushed immediately upon removal with hot water and then clean everything including passages with carb cleaner spray to neutralize it. Pine Sol does attack the zinc plating on the steel parts so you may not want to submerge them and leave them in it.
I have taken to using a Harbor Freight Ultrasonic unit lately with LPS Precision Clean which you dilute with water to get the right mix. Read the instructions carefully because if it's too strong it will eat the aluminum!
Now that everything is cleango thru each passage in the body of the carb with a wire, brush, drill bit, pipe cleaner, etc. to be sure you have removed or at least broken up any deposits in there. Blow thru each passage with spray carb cleaner. Resoak the body again for a few hours and repeat this process.

During this time it's a good idea to go thru each jet to clean it of any deposits. I use a jet gauge
201_4672.jpg 201_4673.jpg
but number drills will work fine.For drill bits choose a size smaller than the jet orifice and work your way up to the sizing. Use a number drill chart like this to match drills to jets. http://bobmay.astronomy.net/misc/drillchart.htm Jets are metric numbering with 100=1mm so a #75 jet is .75mm. You do not want to increase the sizing by using a larger than will fit drill bit.
When you think the emulsion tube holes are clean then clean the inner bore and run thru the holes again, clean the bore and holes one more time.

Some surface plate sanding is in order also while the bodies soak. The air cut valve covers warp, the accelerator pump cover warps, the float bowls warp, the top of the carb body warps. Basically any flat surface of the carb is likely to be warped.
201_4707.jpg 201_4704.jpg 201_4691.jpg 201_4711.jpg
Place a piece of 400-600 grit sandpaper on a known flat surface, marble countertops or Formica work well if you don't have a piece of thick glass , 1/4"+, laying around. Slowly move which ever piece you're working with in a figure 8 pattern until the surfaces are shiny smooth. Usually doesn't take much but until you do it you won't know and not doing it leads to potential air/fuel leaks. Included in this sanding is the Black plastic piston guide the needs to be flat to seal the air bleed chamber.
201_4708.jpg
While you're busy with the sandpaper, lightly sand the overflow standpipe (pic) and inspect for signs of cracks. Cracks show up as thin black lines after sanding. If there is a crack clean it with carb cleaner, add soldering flux and solder the crack closed. The float bowl drain screws are usually corroded and need to be cleaned as well. The corrosion on the taper can be filed and sanded smooth to get a good seal. The seat for the screws can be cleaned with rolled up sand paper pushed into the bore and twist a few times.
201_4739.jpg
 
Last edited:
Inspection and more Cleaning

By now the bodies have been soaked, flushed andcleaned with spray carb clean again.
201_4705.jpg


One more time going thru the passages with wire,brushes, drill bits or whatever fits and cleans.
201_4719.jpg 201_4722.jpg 201_4723.jpg

This includes the 3 idle mixture ports in thethroat
201_4721.jpg

and the air bleeds
201_4707.jpg201_4715.jpg

Blow thru these with compressed air when available, minimally spray carb clean and observe that it comes out someplace.There are no blind holes in a carb, they all connect to some other passage somewhere. Be sure that the float bowl vent is clear as well,
201_4704-002.jpg
that's the little pipe near the linkage and aircut valve inside the carbs.

This includes checking the accelerator nozzles
201_4718.jpg 201_4717.jpg 201_4716.jpg
for flow, cleaning those is a booger since the nozzle port faces inside but they have to be clean and spray or you'll have no pump action and a permanent flat spot.


The air cut valves need to be addressed about now while everything is apart. These valves have to move freely in the bore.Typically they are a bit sticky. Sand the ball of them to get it perfectly smooth.
201_4703.jpg
Roll up some sand paper and insert in the bore twisting it until the bore is shiny smooth.

201_4704-001.jpg
Now test fit the valve. It should slide in and out very easily. If you rotate the carb so the valve is up or down and with alite tap on the carb body it falls in or out it's good. If it doesn't do that,alternate sanding between the ball and bore until it does. Clean all the dust debris with carb spray.

While you're at it check the "check valves" in the left float bowl and the accelerator pump cover. The little ball inside that you can't see is frequently stuck shut which means no accel pump and a flat spot on acceleration.
201_4691.jpg
The hole by my finger is the inlet for fuel,blow thru that with carb clean and watch that it comes out around the square brass plug. DO NOT use compressed air here unless you have to take it apart to clean, more on that! The check valve in the left float bowl

201_4671-001.jpg
gets done much the same, spray opposite the brass plug and it should come out around it. If the float bowl one is stuck you can use a fine drill bit thru the hole and lightly tap it out. Be careful,there's a little irreplaceable spring in there. The ball is just a little ball bearing, 1/8" available in hardware stores. NOW the accelerator pump check valve. There is no easy way. One is to rap on the bottom of it repeatedly until the slug comes out eventually. The other way is to use compressed air. CAUTION That irreplaceable spring is in there too besides the ball and slug. And they will fly out never to be found again. Take a rag and lightly cover it in grease, wrap that around the cover tight and blow the valve apart, the grease will trap the pieces in the rag. Failure to do so will mean buying another cover!







 

Attachments

  • IMG_5239.jpg
    IMG_5239.jpg
    216.3 KB · Views: 37
  • IMG_5240.jpg
    IMG_5240.jpg
    275.1 KB · Views: 42
  • IMG_5241.jpg
    IMG_5241.jpg
    256.6 KB · Views: 31
  • IMG_5242.jpg
    IMG_5242.jpg
    326.7 KB · Views: 35
Last edited:
Reassembly.....finally

So now that everything is so clean you can have your Mother eat off it with no complaints :lol: it's time to start assembly.
First thing to look at is the throttle plate alignment. If it's off it'll look like this. Offset to one side.
201_4713.jpg 201_4654.jpg

The throttle plate should be centered in the bore/venturi. Loosen both screws just enough that you can move the plate. Do Not remove them as they are peened on the end to prevent them from falling out is they become loose and being swallowed by the engine causing major damage. Adjust the plate so you get a smiley face showing.
201_4712.jpg 201_4714.jpg
The throttle plate can be removed, if needed but typically isn't needed, by removing both screws and rotating the throttle so the plate is parallel to the bore/venturi, Be extremely careful not to damage the edges of the throttle plate. The plate is usually stuck and the temptation is to tap on one edge to move it. That will ruin the plate as the taper and edge ground on the plate are a critical fit. Use a pair of pliers, smooth jaw preferred or some cloth to cover serrated jaws, to pull the plate if absolutely necessary. Try to use your fingers only to pull and push. You should mark the plate on one side to denote top/bottom and direction of placement. Once the plate is out the shaft will pull out. You may need to file the section where the screw thread to remove any burrs so when removing you don't gouge the shaft bushings creating a permanent vacuum leak. There is a felt washer for the shaft. If it's ruined or missing you can go to a fabric store and buy a scrap, make a replacement and soak in grease, not oil. On reassembly you will get the smiley face set and the screw tightened. Now while pushing and pulling on the shaft work the throttle to be sure you do not have a bind where the throttle plate is rubbing against the bore. Re-adjust as needed and tighten the screws. Now remove one screw and add a drop of Red Loctite and reinstall. Repeat on the other screw. This will keep the screws from being ingested by the engine.

Now install the jets. This is an excellent time to make any changes to the Primary and Secondary main jets. Also verify that you are installing the correct jetting. See Carb Jetting sticky https://www.vintagehondatwins.com/forums/index.php?threads/64. Be sure to install the Black plug in the open hole by the primary jets.

Float needle is up next. The bore for the needle needs to be clean and polished to prevent sticking. Roll up some fine sandpaper, 1000 grit is good, and twist it around the polish the bore, push it in hard and twist to polish the seat. Shiny brass is what you want.
201_4725.jpg 201_4726.jpg

I also sand the 4 ribs of the needle to be sure there are no burrs that can make it stick.
201_4735.jpg

Float needles are a problem with the VB22 carbs. The after market valves all seem to be too long, causes low float level, or too short, causes high float level.
201_4683.jpg

The only correct length ones I have found are the Honda OEM, expensive, needles.
There is the option of buying the early Black floats, 1978/79 VB21, which are adjustable and allow you to use the cheaper aftermarket needles. Those needles are different than the VB22 needles.
To check float level place the carb face up, air box side, and tip back so the float is just resting on the needle. Now measure, 15.5mm is spec.
201_4732.jpg
You can not measure in either of these positions
201_4729.jpg 201_4730.jpg
 
Last edited:
Reassembly part 2

You can make a float gauge easily by taking a 3x5 card or other stiff material, measure 15.5mm from one edge and the width of the float bowl mating surfaces to form a cut out, cutthat section out and Viola, you have a gauge.
201_4068.jpg
Now that everything is done inside the float bowl install the float bowl with new SS Allen head bolts. Don't forget the small O-ring on the left carb/bowl that seals the accelerator circuit. Install the accelerator pump after installing the dust bellows using new Allen head bolts. Install the air cut diaphragm, spring and small O-ring with the cover and new Allen head bolts. This particular O-ring has a flat side that rests against the carb body.
Re-install the linkage and springs on the left carb if you chose to remove it. Either way be sure to lube the choke linkage pivot bolt so the linkage moves freely. Remove the lock nut and loosen the carb sync screw until it almost falls out.
201_4748.jpgPic
Add the O-rings to both fuel pipes and insert into either carb.
201_4744.jpg
Now align the choke and throttle linkages so the choke link is in the correct position
201_4644-001.jpg 201_4643-001.jpg
and both plates are open and the sync screw has the spring and one washer above the linkage while the other washer and head of the screw is below it
201_4644-002.jpg
Add the metal brackets to make sure everything stays together but don't tighten them yet. There is a little spring that was released on the choke linkage when you took them apart, re-install the hook of the spring at this point so the 2 choke plates open together.
201_4649-001.jpg 201_4650-001.jpg
Check that the linkages are working correctly soboth choke plates do the same thing and the throttle plates as well. Install the separator spring between the 2 throttle shafts at this point. If all is good place the carbs upside down on a flat surface so they both are flat against the surface and snug the screws, rotate the carbs to either face and besure they both lie flat against the surface. You may have to twist them some for that to happen. Once
both surfaces match tighten up the new Allen head bolts you installed.

Now for the pistons, covers, etc. Since the piston has to slide in the cover you need to clean and polish the inside of the coverand the outer surface of the piston, for this I'd suggest using 1000 grit or higher paper, you're not removing metal just polishing it. The piston should fall in and out of the cover when you rotate it back and forth when assembled together. Install the needle and cap screw and snug it, not tighten it. The needle should just float a bit in the piston. When cleaning the needle be very careful of it, it's soft brass and if bent is junk. Don't use sandpaper on it since that will change the mixture. Install the black plastic piston guide that you've sanded flat on the bottom. New ones are in the Honda OEM kit. That flat surface mates to a shoulder that seals the air bleeds so they only get metered air, leaks there can cause a lean condition.
201_4711.jpg
There is a white plastic ring called a piston stopper that is installed next. There's a wide flat bottom side and a thin edged top side
201_4690.jpg
It's critical that it be installed wide side to the body. Besides providing an stop for the piston that ring also set the height of the needle. New ones are included in the Honda OEM carb kit. If you're reusing the old one be sure to clean it until it's white again, NO sandpaper. Slide the piston into the body and install the top stopper in the piston.
201_4685.jpg
That limits the upper travel of the piston which also controls mixture. Make sure it's fully seated in the piston. The picture shows 2 different ones, black is VB22 and white is VB21. Install the spring and slip the cap on. Snug the new Allen head bolts and test the piston lifts and drops smoothly. Now turn the carbs upside down. The piston should stay in it's down position, if not then the spring is weak or wrong. This picture shows the VB21 spring on the
left and VB22 on the right
201_4686.jpgPic
With the carbs upside down push the piston downand release. It should pop back up to the closed position. If not then you'llneed to do more cleaning/polishing to the piston and cover until it does. Oncethat's done snug the screws down firmly, not bloody tight since you'll startwarping it again. Retest piston movement.
 
Last edited:
Reassembly Part 3 and Setup

With the carbs upside down push the piston down and release. It should pop back up to the closed position. If not then you'll need to do more cleaning/polishing to the piston and cover until it does. Once that's done snug the screws down firmly, not bloody tight since you'll start warping it again. Retest piston movement.
Now that everything is cleaned, polished, assembled correctly and moving freely you can perform the bench sync. The purpose of a bench sync is to get the throttle plates in the same approximate position as a starting point so the engine will run. You still have to do a running synchronization after it's running. Use a soft material so as to not damage the throttle plate or bore. I use 1-3 strands of copper wire from a 16/18G wire, pictures show a piece of flattened solder.
201_4745.jpg 201_4747.jpg
Adjust the idle speed screw to open the left carb throttle plate enough to just slip the material of choice between the plate and bore so there's a slight drag like doing a valve adjustment. Without changing the idle speed screw move to the right carb and insert your measuring device. Adjust the Sync screw until you have the same amount of drag as the left carb. To be more accurate use 3 different thickness of material to check a 3 different throttle plate openings. The more you do the closer you will be. In some cases, if you're lucky, it will end up exact when you do the running sync, no final adjust needed. Snug the lock nut, not tighten it yet.
If you haven't already done so assemble the mixture screw in this order: screw, spring, flat washer, O-ring. Install and gently turn it all the way in until it stops. Now turn it out to the correct number of turns as noted here. This is a starting point for mixture, not the final or correct setting in most cases.
Install the carbs, synchronize them and set the mixtures. Best of luck.

Notes:
I did not address setting the choke idle or the accelerator pump clearances due to the fact they are rarely off from the factory and the only time to adjust either one is for altitude compensation or a high idle on choke problem. For that I will refer you to the FSM.

It's recognized that Honda set these engines and carbs to run on the lean side for various reasons. Generally it's a good idea to increase the Primary Main jet 1 size. IE; 72 to 75

There are 2 slightly different idle mixture setting procedures depending on year.
1) Earlier pre 1984 models: Get the engine hot and the bike on the center stand with a fan blowing air over the engine to cool it. Adjust idle speed to 1200 +/-100 rpm. Select either carb, adjust the mixture to obtain the highest idle, reset the idle speed with the idle speed screw to 1200 and proceed to the other carb. Adjust it the same, highest idle speed and reset idle speed to 1200. Repeat one more time, ride 10 minutes and recheck, adjust as needed.
2) 1984 and later: Hot engine, up on center stand, fan blowing to cool the engine. Adjust idle speed to 1200 +/-100 rpm, select a carb. Adjust the mixture screw for highest idle THEN turn the screw in to lean the mixture and obtain a 100 rpm idle speed drop. Rest the idle speed back to 1200 and proceed to the second carb to adjust the same way. Ride for 10 minutes and recheck.

The vacuum ports for synchronizing the carbs are 5mm x .8 pitch. Motion Pro part number 08-0218
Besides using vacuum gauges there is the Edelbrock Uni-Syn #4027 and the Weber STE SK both of which do the sync without the air box boots in place
It's recommended to sync the carbs before making the final mixture adjustment. The sync can change the mixture.
It's easier to remove and install the throttle cables with the carbs off the engine.
 
Thanks for this. I couldn't figure out how to reconnect the "relief spring" as the FSM calls it for linking the two chokes together. I have found with help from your pictures it unraveled one full turn which is why I could never get it on there and get it to work! Got scared I lost an unobtanium spring on the shop floor and even looked around for one!
 
Maybe a stupid question, but I couldn't seem to find the answer elsewhere (and if it's just me bad at looking for it, I'm really sorry!)

Here, and in other posts, you mention that the black floats are adjustable; but how does the adjustment work? Does one simply bend the metal lip that goes into the float needle or is there something else to do?

Cheers!!
 
Maybe a stupid question, but I couldn't seem to find the answer elsewhere (and if it's just me bad at looking for it, I'm really sorry!)

Here, and in other posts, you mention that the black floats are adjustable; but how does the adjustment work? Does one simply bend the metal lip that goes into the float needle or is there something else to do?

Cheers!!
Just bend that tab to get the right height.
 
Dear Long Distance Rider,

Kudos to you and your fine tutorial about cleaning VB22’s. It is the very best one on the web!! Thank you!!

However, even after following your careful instructions, my ’80 CM400 backfired so often I could not drive it, even after cleaning and trying two sets of carbs, 4 times each.
There is an important step that I was overlooking. On a VB22 carb, there is a jet that seems unremovable, so most people do not remove and clean them. This describes what I did to stop the backfiring and get the bike to idle smoothly.

One day I realized that I did not understand how the third set of jets found on Keihin carbs work—the ones with rubber plugs in them-- and why that passageway works only when it has a plug in it.

Mikuni does the job with only two jets, so why the third one, and where does the fuel for the third jet come from with that plug in place?

I went online searching for answers and came across these diagrams, which explained how the fuel flows through these three sets of jets. The second diagram exposes this Keihin “secret.” These diagrams are from a CX500 forum https://www.cx500forum.com/threads/carb-problem.62209/

CARB CUTAWAY 2 KEIHIN VM 22.jpg CARB CUTAWAY KEIHIN VM 22.jpg

The jet with the plug controls the mix at idle, and a little bit off-idle, the “slow” jet—the smaller one, (#72 +/-) controls the mix until the throttle is open enough for the main jet (#118 +/-) to take over. We should call these three, slow, medium, and high-speed jets, but we don’t for some reason, adding to the confusion.

Since the backfires on my bike tended to come at the speeds controlled by the slow jet, the one with the plug), I began to suspect that it was clogged, but had no idea how to get the jet out of its passageway since it has no slots for a screwdriver. So how to get them out? Drill and tap the jets for a small bolt and nut which will work as an extractor.
To see how to extract these “unserviceable” jets, view this video. It uses carbs from a bigger bike, but they have the same design.
https://www.youtube.com/watch?v=SRUnVvHSAf8

By using this method to get the slow-speed jets out, I found that they were totally clogged blocking the passageways, in spite of the fact that they had been cleaned in a pro carb bath and finished in an ultrasonic cleaner 3-4 times. They were so junked up, I had to carefully drill out their orifices, using a drill with a 0.0011 inch diameter. Also needed to drill out the slow carb passageway to the cutoff valve.

backfire Jet 1.jpg backfire jet 2.jpg

Instead of the 4-40 tap the video uses, I went with a 3mm x .0,5 tap, which worked fine. BTW, when drilling the jet, I used a drill press to keep the drilled hole concentric with the jet’s opening; it really helped.

Once these jets and their passageways were cleaned up, and the carbs put back together, the bike started easily and runs great, especially after dynamically balancing the carbs with an antique Motion Pro mercury-tube balancer.

So, if you have been frustrated by backfires, even after trying every typical remedy, try this one. The jets I took out, from all three sets of carbs that I have gone through, were hopelessly clogged—air would not blow them out-- some with junk in them that looked like lime deposits, a few of which I had to gently dig out with some tiny pin-drills.


PS: I also want to thank the person who sent me a set of carb bodies several months ago when I first joined the forum. I lost track of your name, so I could not thank you. I greatly appreciate your generosity. Please let me know who you are so I can thank your personally.

So, as Scotty says, "..rev up your engines!"
 
How does it run now? I have never heard of drilling those slow speed jets, as the internal passageway narrows to the thickness of a fine wire. They are always the culprit when at slow speed or at idle. As you noted removal is the only way to ensure they are clean, since within the bodies they don't respond to any cleaning method if calcified.

Good links and tech tips for sure will help others. Just not sure on the drill method??
 
I went online searching for answers and came across these diagrams, which explained how the fuel flows through these three sets of jets. The second diagram exposes this Keihin “secret.” These diagrams are from a CX500 forum https://www.cx500forum.com/threads/carb-problem.62209/

You might have gone down the topic list to this one:

https://www.vintagehondatwins.com/forums/showthread.php?545-VB-Carburetor-Circuits

The jet under the plug is the slow jet, Your #72 jet is the primary main jet. The jet with the metering rod is the secondary main jet.

I thought we had a thread around here on the issues with the slow jet, can't put my finger on it though.

In any case, congratulations on getting it sorted out.
 
LongDistanceRider, I'm working on a 1979 CM400T. The manual seems to be giving me some confusing info on jet size and location. Primary 70 and secondary 112. Primary goes on the needle tube?
 
LDR; I've finished cleaning up my VB21's and I'm comparing what came in the rebuild kit to what I took out of the carb (singular, doing one at a time). The primary (I think that's what it's called, #31 on CMSNL) that was in there was a 105, and my kit comes with a 75 and a 110. (both are the same physical shape, albeit different bore diameters)
I've not yet pulled the slow speed jet out, fyi (it's on my list, since based on your excellent writeup, it's likely clogged to heck) For the slow speed, tapping it doesn't render it unable to be reused?


-EDIT-
I made a screw driver to remove the slow jet, and that thing does not want to budge, at all. Yeah, it's been soaking in carb cleaner and then I ran it thru an ultrasonic for a few minutes. Still no dice.
Oh, and the mixture screw was missing a spring. I was looking at the kit and saying "huh, wonder what this spring is for, there's nothing that's come out of the carb that resembles it". Fiche clearly shows it, so I can only assume someone has had this apart at one point and lost the spring.

-EDIT 2-
It also looking like the Emulsion tube had the #75 installed. So, they had this jetted backwards?
 
Also, is the "slow speed" jet supposed to be drilled thru (not for the tapped hole, but in oem config)? Mine feels like it's plugged up solid on both carbs, not taking even a .010" gage pin very deep.

-Edit-
Do you have a P/N for the slow jet?
 
The aftermarket slow jets will be fine.
The slow jet has a extremely small hole in the very center, .38mm or .015". They plug up easily and are a booger to clear.
75/105 was the original jetting size with a 110 being optional so you will be fine with a 75/110 combo. However you should use the original 75 jet at least. Kit jets are notorious for being over/under sized. We recommend to everyone to use the original brass when rebuilding any carb. New Keihin jets are available from Jets-R-Us https://www.jetsrus.com/a_jet_kit_street/honda_400_CM400_1980.html
STOP! trying to remove the emulsion tube. 1st shoot some penetrating oil into the hole and let it sit, PB Blaster or Kroil not WD40. While it soaks get a 4mm Allen head socket, 1/4 or 3/8 drive. Round of the 6 corners of the wrench with a file until it just fits the hole. I used my drill press to spin it while filing. Now make a straight blade screwdriver tip on the end that just fits, use one of the other jets to check. It's @1mm width. Once this is done the penetrating oil should have worked to some degree. Insert socket with ratchet and lean down hard on it so it can't slip and apply pressure, it'll break loose eventually. You may need to stop and resoak with penetrating oil for a day if it starts to feel like it's going to break.
Here's a picture of the tool
RIMG0152.jpg RIMG0153.jpg
 
the "drill" I is used is a skinny (about.010 diameter) wire that I cut from a wire brush wheel. After straightening any curls in the wire, I used it to dig out the hardened junk in the jets and it works quite well. Also, in the clogged jets I described, there were hardened lime and calcium deposits, which I cleaned out with a toilet cleaner, the Works, that dissolves lime and calcium. While this cleaner will not burn flesh, it will rust any steel tools left overnight within 2 feet of an open bowl of it, so don't leave it out after using it.
 
Well, I soaked and soaked, poured PB in from both ends over a couple of days. Made up a tool like you recommended, and...I only succeeded in finishing off the damage from the prior owner. Dead in the water, I said to myself "Seth, you're a shop owner dammit, you know how to solve this..." So into the CNC mill it went!
2023-06-06_19h43_54.png 2023-06-06_19h45_08.png

Slow spiral down, cut off all the brass, staying about .003" from the wall. That separated the nozzle from the threads and (with a bit of force) was able to push it out from the other end. A little bit of thread cleanup later and liberal amounts of compressed air and washing, followed by more air, it was good as new.

So, I've got the remnant of the slow jet, and comparing it to the aftermarket, I'm not too certain if I'm going to be okay with them. The number of holes is the same, but the placement is different:
2023-06-06_19h48_24.png
 
Cross posting this, but I found a screwdriver of very similar dimensions to work for the emulsion tubes. Made quick work of it. Wera 05110006001 Kraftform Plus 335 Slotted Screwdriver, 4mm Head, 8" Blade Length.

20230712_100153.jpg

20230712_100157.jpg
 
Last edited by a moderator:
Cross post, but for all years (that I'm aware of) the following o-rings are a drop-in replacement for the carb insulators:

40mm ID x 45mm OD x 2.4mm W.

MCM has 2.5mm W which will fit fine. They have an NBR one that meets the specs, is likely the same as the original: https://www.mcmaster.com/9262K451/

You have a few options though, there's a Viton one: https://www.mcmaster.com/1295N464/

There is also a red silicone one, very good temperature range however does not explicitly state motor oils: https://www.mcmaster.com/5233T719/
 
The Primary #70 goes closest to the mixture screw.
View attachment 21969
There is confusion on this in the fiche. In the fiche it actually shows the primary under the Jet Needle Holder and the secondary under the emulsion tube/"main nozzle". I thought this to be a mistake for the 1979 CM400A fiche, but it's the same problem on the 1979 CM400T fiche. For the 1978 and 1980+ years it IS correct. So beware, apparently it is wrong for 1979 in the fiche and it was never corrected!
 
How does it run now? I have never heard of drilling those slow speed jets, as the internal passageway narrows to the thickness of a fine wire. They are always the culprit when at slow speed or at idle. As you noted removal is the only way to ensure they are clean, since within the bodies they don't respond to any cleaning method if calcified.

Good links and tech tips for sure will help others. Just not sure on the drill method??
The drilling of jets I did had no effect on their mixtures since the drill went into the open end of the jet only about 6 mm, not changing the size of the jet orifice which is located much deeper inside the jet.
Drilling was done only to enable tapping the slow jets in order to remove them.
 
Not strictly carb related, but fuel related. If you need the o-ring for the petcock I have found a replacement from MCM. It's a 11.5mm ID x 16.5mm OD x 2.5mm W o-ring. Original is NBR and I used the same. Part number is 9262K916 get it here - https://www.mcmaster.com/catalog/129/3956/9262K916. They come in packs of 50. Enough to last a lifetime. If someone needs one PM me and I'll throw one in an envelope with a stamp if you're in the US.
 
  • Like
Reactions: J-T
How does it run now? I have never heard of drilling those slow speed jets, as the internal passageway narrows to the thickness of a fine wire. They are always the culprit when at slow speed or at idle. As you noted removal is the only way to ensure they are clean, since within the bodies they don't respond to any cleaning method if calcified.

Good links and tech tips for sure will help others. Just not sure on the drill method??

It runs great, like a factory-tuned Honda! No backfires, starts easily, idles and accelerates nicely. Dont worry about drilling the jet bottom to extract it. The middle pilot jet is at least 10mm long, with many millimeters below its jet orifice, so drilling it has absolutely no effect on the orifice size.

If this still concerns you, how else will you get this jet out? If your bike is running poorly; i.e., bad idle, constant backfiring, hard starting, how else are you going to get the middle (slow) jet out??

Door #2, drill it, extract it, and buy a new replacement jet. Case closed!

BTW, this jet is such a problem with cm400's -- a problem that few people can fix -- that I now shop for cm400's online, looking for ones with this problem and owners who are eager to get rid of them. I got a fairly nice one recently; with a Corbin-like seat, white pearl finish, fair tires and a new battery for $350! Sure enough, the slow jet was well-clogged, not to mention hatchet-job work done to the carbs. After replacing the floats, adding the missing backfire valves, and resynching the carbs, it ran like a Honda. And, with the counter-balancer designed into this engine, it runs as smooth as silk.

PS. Even tho I have reworked over 750 carbs (in 50 years) I had to go through these VB22's 10 full times (!!!) before figuring out how to clean the slow jet. I had used an ultrasonic cleaner, nasty carb cleaning dip, and a combination of both trying to clean that jet. Even so, when I finally got it out, the slow jet was as clogged as it could get, even after 10 tips into cleaning fluids. The slow jets simply have to come out to clean them.

Sorry for my delayed response.
 
It runs great, like a factory-tuned Honda! No backfires, starts easily, idles and accelerates nicely. Don't worry about drilling the jet bottom to extract it. The middle pilot jet is at least 10mm long, with many millimeters below its jet orifice, so drilling it has absolutely no effect on the orifice size.

If this still concerns you, how else will you get this jet out? If your bike is running poorly; i.e., bad idle, constant backfiring, hard starting, how else are you going to get the middle (slow) jet out??

..drill it, extract it, and buy a new replacement jet. Case closed!

BTW, this jet is such a problem with cm400's -- a problem that few people can fix -- that I now shop for cm400's online, looking for ones with this problem and owners who are eager to get rid of them. I got a fairly nice one recently; with a Corbin-like seat, white pearl finish, fair tires and a new battery for $350! Sure enough, the slow jet was well-clogged, not to mention hatchet-job work done to the carbs. After replacing the floats, adding the missing backfire valves, and resynching the carbs, it ran like a Honda. And, with the counter-balancer designed into this engine, it runs as smooth as silk.

PS. Even tho I have reworked over 750 carbs (in 50 years) I had to go through these VB22's 10 full times (!!!) before figuring out how to clean the slow jet. I had used an ultrasonic cleaner, nasty carb cleaning dip, and a combination of both trying to clean that jet. Even so, when I finally got it out, the slow jet was as clogged as it could get, even after 10 tips into cleaning fluids. The slow jets simply have to come out to clean them.
For clarification, you are describing the issue with the jet you show in Post #11 above with the crud all over it,
and not the emulsion-tube-nozzle GearSoup shows in his Post #21 above, am I correct ?

My two '82 Customs came used with different VB22 carbs - a correct VB22G on one, and a VB22A on the other.
There's several VB22 variations, and I'm still learning, noting the differences, trying to lessen the complexities :
VB22A
VB22B
VB22C
VB22E
VB22G
VB22J
VB22JN
 
Well, I soaked and soaked, poured PB in from both ends over a couple of days. Made up a tool like you recommended, and...I only succeeded in finishing off the damage from the prior owner. Dead in the water, I said to myself "Seth, you're a shop owner dammit, you know how to solve this.
View attachment 22286
LDR I didn't read all the way back into the beginning of this thread initially and you did an excellent job with your tutorial on cleaning these carbs. These and the early Goldwings carbs are the toughest to get right IMO.

MY SOLUTION:

Having cleaned my share of CV carbs, if that emulsion tube as pictured is not damaged by a PO or yourself then here's my sure fire way to properly remove it. First get a correct sized flat blade screwdriver that fits the slot ears perfectly with no slop. I custom ground one for a tight fit for that top slot and you may need to do the same.

Using a small pin torch heat around the carb tower area where that emulsion tube sits for 30-45 secs, then place the blade into the slot and tap the top lightly to disturb the bond in the threaded section. Then twist the screwdriver carefully and it will break the old gas varnish bond and screw out relatively easily.

This method has never failed me. I have removed many of those emulsion tubes from banks of four CV carbs on four cylinder bikes over the past 15 years. I damaged a few initially, before I figured the above method out.

Do not force the emulsion tube, if it doesn't break free after this procedure. Stop and reheat the tower again and try until it lets go. :)
 
Last edited:
LDR I didn't read all the way back into the beginning of this thread initially and you did an excellent job with your tutorial on cleaning these carbs. These and the early Goldwings carbs are the toughest to get right IMO.

MY SOLUTION:

Having cleaned my share of CV carbs, if that emulsion tube as pictured is not damaged by a PO or yourself then here's my sure fire way to properly remove it. First get a correct sized flat blade screwdriver that fits the slot ears perfectly with no slop. I custom ground one for a tight fit for that top slot and you may need to do the same.

Using a small pin torch heat around the carb tower area where that emulsion tube sits for 30-45 secs, then place the blade into the slot and tap the top lightly to disturb the bond in the threaded section. Then twist the screwdriver carefully and it will break the old gas varnish bond and screw out relatively easily.

This method has never failed me. I have removed many of those emulsion tubes from banks of four CV carbs on four cylinder bikes over the past 15 years. I damaged a few initially, before I figured the above method out.

Do not force the emulsion tube, if it doesn't break free after this procedure. Stop and reheat the tower again and try until it lets go. :)
Yes, grinding a screwdriver to fit is critical. Heat is a good assist in removing them as well.
I wrote this up years ago on the other forum after fighting with these VB series carbs and several long conversations with Larry Cargill who deals with the CX models as well as Goldwings. He published a book on doing them http://donlhamon.com/carbbook.html
There were so many failed rebuild attempts at the time that I just had to try and do something to help out.
 
For clarification, you are describing the issue with the jet you show in Post #11 above with the crud all over it,
and not the emulsion-tube-nozzle GearSoup shows in his Post #21 above, am I correct ?

My two '82 Customs came used with different VB22 carbs - a correct VB22G on one, and a VB22A on the other.
There's several VB22 variations, and I'm still learning, noting the differences, trying to lessen the complexities :
VB22A
VB22B
VB22C
VB22E
VB22G
VB22J
VB22JN
That's a crazy number of variations.
 
Yes, grinding a screwdriver to fit is critical. Heat is a good assist in removing them as well.
I wrote this up years ago on the other forum after fighting with these VB series carbs and several long conversations with Larry Cargill who deals with the CX models as well as Goldwings. He published a book on doing them http://donlhamon.com/carbbook.html
There were so many failed rebuild attempts at the time that I just had to try and do something to help out.
In the several VB-22 carbs I have rebuilt, the slow jets were not slotted so there's no way a screwdriver can get a hold of them. Some later Keihin carbs had slotted slow jets, but the early-80's VB-22's did not, leaving the screw-extraction method as the only viable option.
 
In the several VB-22 carbs I have rebuilt, the slow jets were not slotted so there's no way a screwdriver can get a hold of them. Some later Keihin carbs had slotted slow jets, but the early-80's VB-22's did not, leaving the screw-extraction method as the only viable option.
The screw in slow jets started with the VB22G carbs, prior versions were press in.
 
Hey LDR, I know you stated that aftermarket jets are not the correct sizes and should refrain from using them, however I wanted to know what you would think about the washer/o rings that come with the aftermarket kits to replace the old ones? Are those still usable as well?
 
Hey LDR, I know you stated that aftermarket jets are not the correct sizes and should refrain from using them, however I wanted to know what you would think about the washer/o rings that come with the aftermarket kits to replace the old ones? Are those still usable as well?
The rubber parts should be fine.
 
The screw in slow jets started with the VB22G carbs, prior versions were press in.
Dear LDR, thank you for letting us know that VB22G slow jets are slotted. Very helpful information!
Quite often I need information like this but don't know where to get it. Is your source a particular book or set of books? If so, which book(s) should I get?
Thank you again for your very accurate and insightful information. Cheers, Roger
 
Dear LDR, thank you for letting us know that VB22G slow jets are slotted. Very helpful information!
Quite often I need information like this but don't know where to get it. Is your source a particular book or set of books? If so, which book(s) should I get?
Thank you again for your very accurate and insightful information. Cheers, Roger
No books, just dealing with the different versions and making notes. I've bought a lot of "junk" carbs in the past off eBay just to experiment with.
 
They're fine to use, however the accel pump rod could be too long requiring some trimming to length.
LDR, thank you for this service. After making my previous mistake (you mightve seen on my othed thread) im making sure to read your instructions very carefully and clarifying as much as i can. I appreciate your patience with me.
 
a few more questions and I’ll try to ask whatever I have so you can just answer all at once.

For the air cut off valves, what grit sandpaper do you use to sand down the bore and ball of the air cut off valve? What grit would you use for the bores made up of brass?

Since your replacing the screws, do you still use the original crushwashers/washers with the allen screws or do u not use em at all? Replace em?

My issue with my bike was that the the bike was leaking lots of fuel through my right overflow tube, when I took apart my carbs, they looked pretty clean (except for the overflow bowls). I inspected the needle and the bore and things (to me at least) looked good and clean so I couldnt see why it was getting stuck, I’ll attach some pics here of what the specific side of the bike that was leaking looks like.

One last thing (for now) is do I have a different type of air cut off valve (this is the one that came out with these carbs) than you? Should I still sand this to get it smooth? I wasn’t too sure cuz of how small the end is.



8334987C-5603-45C9-B0FA-98806C90F016.jpeg5890E752-606E-4951-975B-49991C9D49CB.jpeg8A81DEF0-6747-4FA1-91DD-F176CD00905F.jpeg
 
You have the later pintle type air cut valve. The length is a critical factor. That type doesn't seem to have a sticking issues so not need to try and sand the bore, I don't think it's really possible. Personally I block the vacuum port to that valve and assemble with all the bits in place. It results in so decel afterburn popping at times and eliminates a potential undiagnosable vacuum leak.
I use regular lock washers where there were originals, can't easily remove the ones on the old screws.
It sounds like your original fuel leak was maybe due to a cracked overflow stand pipe, the brass tube in the center of the float bowl. Sand that tube a look for a fine black line which would be the crack. Easily fixed by flux and solder.
 
You have the later pintle type air cut valve. The length is a critical factor. That type doesn't seem to have any sticking issues so no need to sand the bore, I don't think it's really possible. Personally I block the vacuum port to that valve and assemble with all the bits in place. It results in some deceleration afterburn popping at times and eliminates a potential undiagnosable vacuum leak.
I use regular lock washers where there were originals, can't easily remove the ones on the old screws.
Pintle-type as in straight shaft or pin on that air cut valve showing in that plastic baggie. Yeah, no need to sand that pintle - sanding is for the type with the round metal ball type ones where yours only has a straight pintle.
Regarding the float needle valve photo - I see the gas line(s) around its rubber tip but I can't see if there is a groove or notch in the rubber that happens with age and with a full float bowl of gas pushing the float up and thus the float needle valve up and holding it in its brass seat of the carb body.
The groove/notch develops as the rubber tip hardens from age, old rubber. If you push on the rubber tip both straight on and push at it from an angle with something that won't cut the rubber AND the rubber tip is still plenty flexible, supposedly you can keep using that float needle valve.
At its other end is a compressible pintle with a tiny spring between the pintle and the body of the float needle - when you push it in does it return itself back out and push in and out without feeling any crud or resistance ?
I don't know the purpose or function of the springed-pintle opposite the pointed rubber tip on these float needle valves, but it must do something or it wouldn't be built into them.

Lastly, because I have ball-type air cut off valves in my carbs, I used the skinny-narrow wire brush in this kit in my rotary tool (Dremel) to clean the white powdery stuff in the air cut valve bores on the side of my carb bodies (my bikes sat unused in a barn and shed for decades before I bought them) :
 
You have the later pintle type air cut valve. The length is a critical factor. That type doesn't seem to have a sticking issues so not need to try and sand the bore, I don't think it's really possible. Personally I block the vacuum port to that valve and assemble with all the bits in place. It results in so decel afterburn popping at times and eliminates a potential undiagnosable vacuum leak.
I use regular lock washers where there were originals, can't easily remove the ones on the old screws.
It sounds like your original fuel leak was maybe due to a cracked overflow stand pipe, the brass tube in the center of the float bowl. Sand that tube a look for a fine black line which would be the crack. Easily fixed by flux and solder.
Should I go easy on the seat of the float valve (the bore of it) with 1000 grit sand paper or go with 600? Also the vacuum port, is that the one that leads to outside the carb? Is there any performance/health of carb issue that can be caused from blocking it?

I’ll sand the brass with whatever sandpaper grit you recommend and see if there are any cracks. Will update soon.

Boosted, I’m gonna check today the conditions of the needle and get back to you. From what I remember, it didnt seem to have a groove.
 
Back
Top Bottom