Electronics Guru's Needed

[512tr]

Dave is right (as always)…..

Some further comments.
Nice to hear that it starts, you are on the right track

But, with a unknown history of your carbs and the symptoms you are describing, do the “obligatory”…..Do the carbs!

The CBX 6 carb-rack is a masterpiece, but it is not rocket science, so all with relatively fair technical skills and insight could rebuild them.

The most common problems with CBX carbs are hard starting, lack of idling and carb progression…. due to clogged pilot jets.

When it is running as you describe on the bench in the garage, the only fuel contributor is the pilot jet circuit, The Dynajet stuff should not be involved unless you are hard on the throttle.

When I did my carbs (after the engine rebuild) I tried to collect as much information as possible to understand how the CBX carbs works. I did some illustrations in order to educate myself and try to understand the different processes.

If I’m wrong in something, please “arrest” me….I’m learning new things every day.

It is all about the pilot jets.....

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Dynajet Stage 3:
According to Dynajet, the clip should be at the second grove from the top.

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Note!
My experience with Dynajet 3 is that my engine was running far too rich, even with the smallest main jet DJ122 and needle in lowest position (clip in upper grove).
(I have an 80 mod. with the relatively rare VB65A carbs, bored with 67,5mm Wiseco pistons (CR 10,25:1), individual pods and custom exhaust.)


Accelerator pump:
It is easy to check if it’s working, just twist the throttle fast, at the same time as you observe if it injects fuel through all 6 spray nozzles (you don’t have to start the engine).
BTW, the accelerator pump is not a vacuum pump, it’s a 100% mechanical membrane pressure pump, un-dependent on carb vacuum or engine running.

Your observations deviate 180 degrees:
- That you have throttle response only with choke on, indicates lean mixture, if your engine is warmed up. A cold engine will hesitate when
giving hard throttle without choke, that’s normal.

- That you have unburned fuel at the exhaust indicates an extremely rich mixture. If it is unburned fuel, you should smell it, ensure
that the droplets are not H2O (water), which is normal during cold start combustion.
If it is unburned fuel, it could be misfire….recheck your ignition, be 110% sure that all your plug wires, coil wires are routed correct.

[Larry Zimmer]

Great illustrations. Thank you. Enjoy your project and ride. Happy 2025 for you.

[512tr]

Thanks Larry, same to you

[Fw66]

Once again, thanks for all the instruction- I figured there was no way around but to remove the carbs and inspect!

Tasks Completed:

1. Adjusted the idle fuel mixture screws to 2.5 turns out while carbs still on the bike. Noticed a significant improvement in idling already.

2. Removed the carbs and changed all clip dynajet needle positions to the second from the top + 2 washers.

3. Readjusted all fuel mixture screws to 2.5 turns out (more precisely done with the carbs off the bike).

4. Removed all pilot air jets and sprayed compressed air through the jet, jet holes to remove any blockage.

5. Eye checked all transfer progression ports for any visible blockage + sprayed compressed air.

6. Confirmed accelerator vacuum was installed correctly.

Questions

1. Jets are stock (I never changed them)- my air pilot jet is a 35 and my main jet is a 105: given that I am supposed to be following the stage 3 instructions, I'm thinking I need to go to 130 Jets as the instructions state? Are there any glaring issues with using 105 on this setup based on dynajet needles (second from the top position) + tims 2x3 pods + stock carbs + 3 into 1 into 2 exhaust?

2. I'm missing the black plug that sits on top of the carb piston (that goes into the top carb cover) on one of the carbs- this probably is ok correct?

2. I only have the main jet and the pilot air jet on all the carbs, I'm guessing this is because i have the 62 carbs- not sure what you referred to as removing the pressed-in jet?

3. Possible issue: I noticed that when the butterflies were opened, there was no movement on the accelerator rod at all. Upon closer inspection, I saw that the lever that would mechanically push the accelerator rod was bent on one side, which prevented the entire lever from moving. I'm guessing this could be one of the reasons the engine dies when the throttle is twisted?

I used some pliers to straighten it and now opening the throttle moves the lever. However, once the lever moves, I also noticed it wasn't pushing down on the accelerator vacuum smoothly. It actually looks like the piece of the lever that would contact the accelerator rod is chipped off? It kind of gets stuck behind the rod now when it moves which I assume means I need to replace the part.

[daves79x]

You've got a lot going on there. I think you are closer on the clip position. You MUST determine of your main jets are Dyna or Keihin. A 105 Dyna is probably close to correct for pods. A 130 Keihin is sort of equivalent to the 105 Dyna. You have screw-in #35 slow jets. These carbs are VB64, '82 version, if that's the case.

Yes, you need the plastic stopper caps on the slides.

I can't see exactly, but it does look like your accelerator pump arm is broken. So do you plan on separating these and fixing the problems?

There is a lot more to testing the circuitry for good flow than you've done so far. If you are serious about getting these right without taking them off 2 or 3 more times, contact me and I'll be happy to walk you through a bunch of stuff.

Dave

[512tr]

It looks like you have several carb issues, a complete rebuilding is overdue.

Sooner than later, you will need to split the carb rack and replace the O-rings (without knowing the carb history, they could be +40 years old)

You may have the stock Keihin105 main jets and not the DynoJets, check if it has the star-shaped K stamped on it.

Picture of my old 105 main.

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If you have the original Keihin needles, use them instead of the Dynojet needles, if you don’t have them try to get hold on some (or Keyser if you can’t find Keihin)

You mention you have the VB62 carbs, I think you need the 55F needles, others familiar with these carbs may confirm if this is correct.

As I understand it:
The black rubber plug at the top of the vacuum piston is a bumper/stopper, to stop the vacuum piston in upper position.
Without it, the vacuum piston will go approximately 4,5 mm too high at WOT at high rpm, thus causing the jet needle to rise 4,5 mm higher in the needle jet…..As a result, a much richer AFR from this carburetor, at high rpm.

Tuning and finding the correct jetting is the last thing you do, AFTER you know the carbs are in 100% good condition.
Start with the stock setup (only richer on the idle mixture screw) and see how the engine behaves and take it from there.

Take Dave's offer to guide you during the carb rebuild, you are in the best hands.

[Fw66]

To my relief, the accelerator lever was pretty badly bent but not chipped off.
I was able to straighten everything and reinstall- moving the butterflies now properly moves the arm and pushes the accelerator rod down.

I checked the jets and the 105 main jets I have on do not have the K stamp which leads me to believe they are Dyna 105's. Is there any other way to be sure or is this an assumption ok to make at this time?

I also have a replacement piston cap ordered and on the way!

@Dave- am I at the point good to put the carbs back onto the bike to bench test?

[daves79x]

Those are Dyna main jets. Such as it is, the Dyna set-up you have is pretty much the way it should be. Can you please verify that you have VB64 carbs? They are the only ones with screw-in pilot jets, which you showed. I think you claimed they were VB62, which cannot be.

Do you know if/when the carbs were completely separated and the o-rings replaced? You are just fooling yourself if you do not know and go ahead and use them this way. Original o-rings are all leaking by now and early aftermarket ones were not Viton (some still aren't). You should really consider doing all that before further testing and installation. But if you want to roll the dice, you can wet test them on the bench. I think there is still circuit testing you need to do, but looks like you have them all buttoned up now. Put gas to them, prop at about the installed angle. Test the accelerator pump. You should get a strong squirt from all six when blipping the bellcrank. I'm doubting that you will - there are a lot of moving parts that you have fiddled with in that system. Even with the best efforts it's sometimes a challenge.

You need to carefully bench sync the carbs before installation also. Not sure where you are in that process.

It also looks like you have the bowl vent hoses routed incorrectly. They should exit above the upper rear carb frames. Where you have them, it will be impossible to get the tool in to gauge (or bench) sync them.

Dave

[Fw66]

Hey Dave, yea they are VB64 carbs because all have the screw in pilot jets.

As for the carbs- these came off of a fully running 1982 prolink which I purchased about 5 years ago. The previous owner was on these forums but to your point I don't know if these have for sure been split apart. They have definitely been worked on as I have had to replace rounded out screws and see signs of prying/flathead marks in a few places. Either way, I have already wet tested these carbs on the bike and didn't find any leaks around the fuel joints as I troubleshooted my previous issues around mis-wired ignition timing and rough idling.

I'll give the accelerator pump a test today.

I have bench synced the carbs by adjusting all butterflies to just barely cover the first progression port: started from carb 4 then went to 5/6 and then 3/2/1. Not sure if the picture shows much but attached!

[daves79x]

Couple of things I see - the air cut connector tube between 5 and 6 looks pretty dodgy. Hope it's not cut through. Then one connector joint is missing the rubber covers. This is not good. Dirt will get into the joints and you cannot get a reliable sync with those missing. I fear you will regret not completely rebuilding these.

I've said this many times - the carbs are the heart and soul of the CBX. If they are not right, does not matter how much other work, expense and bling was done, it'll never be right.

Dave

[Larry Zimmer]

Carb work might be an effort. However, believe me -- DAVE KNOWS WHAT HE IS SAYING!! Follow his advice/thoughts/etc or you will be chasing ghosts forever.

[512tr]

There is no “quick fix” for old and mistreated CBX carbs, do it the right way…. just saying.

[Fw66]

Hey all- thanks for the feedback about the carbs, I am working on them!

I wet tested the carb circuitry and to no one's surprise, Dave was right again. I was only able to get fuel to squirt out of carb 3 when manually pumping the accelerator rod.

1. I figured I needed to clean the accelerator circuit so I adapted a nozzle to fit into the fuel port on carb 3 and sprayed carb cleaner through. After a mix of air and carb cleaner, I was able to get consistent and strong spray out of all six accelerator fuel ports beside the choke plates.

2. After reading some other forum posts, I noticed that I was missing an o-ring between the the accelerator pump body and the float bowl (7mm o ring i believe?). I saw a little bit of fuel escaping the accelerator pump body and the bowl and so replacing this should help.

I havent wet tested the carbs again since confirming spray out of all 6 accelerator ports- is there anything else I should check for before retesting?

Thanks!
F

[daves79x]

You should be testing the low-speed circuitry for good spray out the three progression holes in the carb throat. You have to plug various passages to get the best test.

Dave

[RC 166]

Here are a couple of photos that may help everyone understand the importance of drilling/tapping/extracting the aluminum plug, near the mixture screw tower.
Crud can/will build up there, and like a ship in a bottle, can't be removed the same way it got in there.

I've found that carbs in general, with age, the worse they get. I've had to do this as a precaution for some time now, on EVERY rebuild.

After ultra sonic cleaning, I reinstall the plug with a thin coat of epoxy to insure sealing.

The cut-away carb is a CB900F example, which is very similar to the CBX

Treat this as gospel.

Can you please share tap size, drill depth etc... how to do this. Any pictures?