[kontiki891]

Thought I would share my research on the rebuild kits for those twin Keihin CVK 34's.

EDIT: Notes on actual rebuild process have been added.

Online you can find many kits advertised for $22 or so however they are usually missing crucial items, and the machining of the brass may not be as precise. Don't scrimp on these precision parts which are the heart of your fuel system.

The CVKs have these parts which are replaceable.

I call the Drain the Jet Chamber, sounds much better and is more descriptive, no?

The Choke Plunger is also known as the Starter Plunger.

Most people in the industry call the Coasting Enricher the Air Cutoff Valve.

Here is the list of must have parts:

• Main Jet #132
• Jet Needle (N53A front and N53B rear. Be very careful not to order qty 2 of a single rebuild kit, as you would then not get the different jet needles!)
• Needle Jet Holder "F" (While the Service Manual labels it the Needle Jet Holder, it is technically the Main Jet Holder. The actual Needle Jet Holder is pressed into the bottom of the slide bore).
• Pilot Jet #38 (also called Slow Jet)
• Pilot Screw with spring, washer and o-ring (often called Pilot Air Screw, but on the CVKs it is on the fuel side, so I believe it should be called Pilot Fuel Mixture Screw).
• Float needle
• Float chamber O-ring
• Jet chamber O-ring
• Coasting Enricher (aka Air Cutoff Valve) O-ring

Here is the list of parts to replace as needed:

• Choke plunger (also called Starter) with spring, seat and cap
• Coasting Enricher diaphragm aka Air Cutoff Valve
• Screws for Float chamber
• Screws for Jet chamber
• Screws for Coasting Enricher
• Screws for Vacuum slide

Rarely need to replace:

• Float
• Jet chamber drain plug
• Vacuum slide diaphragm, spring and seat
• Coasting Enricher spring

Available Kits:

All Balls Racing rebuild kit $48 online has float & jet chamber gaskets, pilot screw with spring and washer and o-ring, jet needle, main jet, pilot jet, float needle, enricher (air-cutoff) chamber and passage o-rings, and replacement screws for float chamber, jet chamber and coasting enricher. Missing choke plunger & enricher air cutoff diaphragms.

EDIT: It is also missing the Main Jet Holder, which is labelled Needle Jet Holder in the Service Manual. On Amazon their ad says the Needle Jet Holder is "pressed in" which is true. Normally the Needle Jet Holder has the Main Jet screwed into the bottom, and the Jet Needle fits directly down into it. On these CVKs the Main Jet has its own holder "F" which unscrews. I believe lots of people call it the "Emulsifier Tube", and it routes through an internal passage to the actual Needle Jet Holder. Only the Niche Cycle Supply kit includes this "Main Jet Holder".

Niche Cycle Supply has an excellent $39 kit that includes gaskets for float and jet chambers, jet needle, choke plunger, float needle, pilot screw with spring and washer and o-ring, needle jet holder (actually the main jet holder), idle adjustment screw (oddly...not sure on this usage, comments welcomed!), pilot jet and main jet. Missing screws for float and jet chamber and coasting enricher, enricher o-ring and diaphragm.

Chinese version of the K&L kit 18-9341 $22 eBay includes float chamber gasket, float needle, main jet, jet needle, pilot screw with spring and washer and o-ring, float chamber screws, enricher o-ring, jet chamber screws and jet chamber gasket. Missing pilot jet, needle jet holder (main jet holder), enricher diaphragm, screws for jet chamber and coasting enricher!

Japanese K&L rebuild kit $50 from Dennis Kirk includes gaskets for float and jet chambers, pilot screw with washer and o-ring (but no spring!), float needle, choke plunger cover (oddly!), pilot jet, and float chamber screws. Missing needle jet holder (main jet holder), jet needle, main jet, pilot screw spring, enricher o-ring, enricher diaphragm, screws for jet chamber and coasting enricher! (hard to believe it is missing all those parts, but I have verified that this is the case).

Hope this helps you with all those detailed parts, and your comments are welcomed!

 

[4StringFarley]

JBM industries does still sell the Vacuum valve diaphragms (I purchased a set first week of Decemeber 2020). Quick service and at $20 a pop it's a lot better than the $150+ that most sellers ask.

 

[kontiki891]

JBM industries does still sell the Vacuum valve diaphragms (I purchased a set first week of Decemeber 2020). Quick service and at $20 a pop it's a lot better than the $150+ that most sellers ask.

I’m gonna check that out. I noticed only K&L Japan says their rubber is Viton. I’m an engineering freak on the details. They’re sure making their $ on markups it seems.

 

[Spockster]

Viton is great with ethanol gas. The low octane kit for the outboard came with viton tipped needle valves.

I see coast enrichers on eBay two for $25, some at $10 each. For some reason all the ebay sellers call them air cut valves.

If their listings are correct, the KLR650 uses the same part.

 

[kontiki891]

Viton is great with ethanol gas. The low octane kit for the outboard came with viton tipped needle valves.

I see coast enrichers on eBay two for $25, some at $10 each. For some reason all the ebay sellers call them air cut valves.

If their listings are correct, the KLR650 uses the same part.

Yes you can save lots if you choose. I saw basically three kits out on eBay: Made in Taiwan, China, or Japan by K&L.

I decided to get K&L diaphragms but only because the others did not mention Viton rubber even though the pics of the Taiwanese mfg looked similar but how can I know looks can be deceiving.

I want the best in the carbs since they breathe life into the Vulcan. And Amazon ships fast so I can pick them up at the drop off locker tomorrow. So I paid $29 each but I had my gift card still that my daughter gave me for Father’s Day so that just about covered it.

 

[kontiki891]

Yes you can save lots if you choose. I saw basically three kits out on eBay: Made in Taiwan, China, or Japan by K&L.

I decided to get K&L only because the others did not mention Viton rubber even though the pics of the Taiwanese mfg looked similar but how can I know looks can be deceiving.

I want the best in the carbs since they breathe life into the Vulcan. And Amazon ships fast so I can pick them up at the drop off locker tomorrow. So I paid $29 each but I had my gift card still that my daughter gave me for Father’s Day so that just about covered it.

Oh yeah by now you probably googled it. The “coasting enricher” cuts off air making the circuit rich with fuel.

When you close the throttle quickly air can flow through the idle air circuit. So the mixture is very lean and without enough fuel to ignite. So that unburned fuel gets ported out into the exhaust pipes which are hot enough that they ignite it 💥 boom when enough accumulates.

The coasting enricher pulls a vacuum at closed throttle, moves the diaphragm, cuts off the air flow which gives you a rich mixture and so the fuel ignites in the cylinder instead of the pipes.

The only thing that wasn’t certain is the flow of air. Since it’s a “cutoff” it has to stop an existing flow. We talk about jets a lot but only the fuel jets. There are three air jets: main, pilot and starter but they are permanently pressed in so we pay them no attention. I’d love to see an internal cutout of the CVK to show the full flow of all fuel and air and ports.

 

[Spockster]

Then there's all the air bleeds, many good carbs have been condemned as "bad" and tossed in the junk because of a simple clogged air bleed.

On some bikes the air bleeds look like magic, you cover the air bleed with your fingertip and gas will pour from the overflow. One guy thought I broke his carb.

A 4150 Holley will dribble through the transfer slots if air bleeds are clogged. People will blame this on a porous carb body and toss it in the trash.

Air bleed - Those brass balls pressed into holes. Some function as a siphon break.

This thread keeps getting hidden, after I post in it, I can't find it until someone else posts in it.

 

[kontiki891]

Then there's all the air bleeds, many good carbs have been condemned as "bad" and tossed in the junk because of a simple clogged air bleed.

On some bikes the air bleeds look like magic, you cover the air bleed with your fingertip and gas will pour from the overflow. One guy thought I broke his carb.

A 4150 Holley will dribble through the transfer slots if air bleeds are clogged. People will blame this on a porous carb body and toss it in the trash.

Air bleed - Those brass balls pressed into holes. Some function as a siphon break.

This thread keeps getting hidden, after I post in it, I can't find it until someone else posts in it.

You are one step ahead. haha.. Yesterday I bought a small tube of anaerobic gasket sealer. The reason is exactly as you said, I have been hearing about lots of air leaks,, especially in the rubber boots, but here is the reason I bought this sealer:

First, there is a guy who has been rebuilding Bing CVs for years, and he has a guide (I will try to link to it later) and he cautions about how to avoid air leaks. He does a coupla things including using wet-dry sandpaper like the #300 I think and a flat surface and runs the carb mating surfaces over it just a few times in a figure-eight motion. Then he applies silicon grease very sparingly with a q-tip.

Second, when I disassembled the four covers: vacuum slide, float chamber, jet chamber, air cutoff (or coasting enricher!) I noticed that there were sealers used as follows: in the vacuum slide, float chamber and coasting air cutoff the o-ring channel had been filled carefully and sparingly with a light yellowish grease, which I take to be silicon grease.

The jet chamber o-ring channel was very very carefully and expertly sealed with a line of orangish elastic material in the groove of the outer edge only, not filling the channel enough to make the o-ring immersed in it. Looked like some kind of gasket sealer. So it got me thinking: these carbs are not designed to be sealed by o-rings alone; we should give them some help!

I don't think the carbs had been opened before, so these expert sealing techniques would have been done by experienced factory engineers.

I can't find silicon grease yet, checked a coupla auto-parts stores and the motorcycle dealer. They all have silicon spray lubricant or lithium grease.

UPDATE:
Ace Hardware has a nice small 1/2-oz tub of Silicon Grease.

Super Lube has O-Ring Silicon Grease in a 3-oz tube P/N 93003.

 

[Spockster]

It does appear that the factory may have used some type of sealer. But myself, I never use any sealer on carbs and only some brush tack on automatic transmissions.

Migration of the sealer into passages is a nightmare.

 

[kontiki891]

It does appear that the factory may have used some type of sealer. But myself, I never use any sealer on carbs and only some brush tack on automatic transmissions.

Migration of the sealer into passages is a nightmare.

Updating:
The All Balls Racing carburetor rebuild kit P/N 26-1722
for the VN750 does not include the Needle Jet Holder. Their Amazon ad says it is "pressed in". Usually the jet needle fits directly into the Needle Jet Holder at the bottom of the bore.

But on the CVKs there is an internal passage from the pressed-in Needle Jet Holder to a Main Jet Holder "F" into which the main jet is screwed. So it is the Main Jet Holder that is missing from their kit. Only Niche Cycle Supply has a kit which includes every removable piece (see post #1 which I have now edited to be more accurate).

Also, replying to Spockster, I hear you about gasket sealers contaminating the gas. I will try to get by without anything other than light silicon grease in the o-ring grooves, which is what I found was there from the stock factory carburetors. If it isn't broke, I will not fix it; only if it leaks will I revisit the o-ring sealing.

Somehow Santa Clara Cycles screwed up and shipped me the K&L Rebuild Kit. It is missing way more stuff than All Balls, including main jet holders, jet needles, main jets, and pilot screw spring. So this is taking way more time than expected, but I will be patient and try to get it done right and in a quality way.

EDIT: Because I found All Balls Racing rebuild kit was missing the "Needle Jet Holder F" I ended up switching over the Niche Cycle Supply kit.

 

[kontiki891]

Notes on the actual rebuild process.

1. Niche Cycle Supply rebuild kit used because it has every jet and holder needed, while every other kit I could locate was missing some vitals (details in original post #1).

2. Ordered new screw hardware from local dealer. He doesn't charge OEM which is good otherwise those hair cotter pins on the throttle linkage will set you back $4.20 each. The hex head jet chamber screws were discontinued, but not critical since hex heads do not get beaten up.

3. Use JIS P.2 x 100 screwdriver otherwise you will burr up the screw heads with regular Phillips #2.

4. The pilot jet (aka slow jet) on my good carburetor was blocked solid. No compressed air would clear it. A tiny wire could not clear it (see photo). It would require a very stiff tiny wire, or perhaps after soaking all night in solvent (Liquid Wrench or ChemTool) it would come out. This is FYI that these jets are definitely a problem area. I am replacing mine.

EDIT: There was conflicting info on the forum about jet needles. Double-checked that this is correct:

5. The stock jet needles front/rear are N53A and N53B. The rear is a bit longer and thinner. The Niche rebuild kit came with D635 front and D636 rear which was the longer thinner one. They are said to match the OEM exactly.

6. The Niche kit choke (aka starter) plunger is different (see photos). The stock unit has a cylindrical extension about 5.5mm long, while the Niche unit is missing that altogether. Likely the Niche unit will block the airflow adequately to provide a rich mixture for starting but this also bears watching.

7. The washer supplied by Niche for the pilot mixture screw is too large in diameter to fit in the threaded chamber (see photos). Surprised at this, it should be caught by their quality control; I will contact them to let them know. So don't lose your old washer as I did, and have to spend time getting the replacement.

8. I used the SuperLube O-Ring Silicone Grease 93003 to fill the channel in the vacuum slide. This sticky grease held the diaphragm in the groove nicely. I rubbed some in on the top outer diameter to seal the groove completely before putting on the cap, so it is very airtight.But don't get any inside the bore.
You can see before the rebuild that the channel came filled with grease from the factory.

9. The front carburetor vacuum slide was sticking when used the manual test. It did have the nice whoosh sound, but if I pushed both slides up and released at same time I would hear thump as the rear slide hit down first, then thump as the front slide hit. No good. I took it apart and used 2500 wet dry to clean up the slide and the bore and this solved that completely. Both slides and bores hugely benefited by being buffed up.