Topic: Keyster PD 46A carburetor (Honda CB 550 K3) questions

[Julius]

Hi!

I am restoring a Honda CB 550 K3 (built in 1977 for the European market) and have a few questions about the Keyster PD 46A carburetor. Although I have red most of the relevant posts here, I did not find answers to those questions and I hope you can help.

First question: The installed emulsion tube has a slightly different arrangement of holes than the one included with the Keyster gasket set. See attached photo. I would simply continue to use the existing emulsion tube. What do you think?

Second question: The choke flaps were previously screwed to the choke rod with the familiar hollow screws (to prevent them from loosening due to vibration). I would replace the screws with stainless steel screws with a spring washer for security, or is there any reason not to?

Third question: My carburetor was missing the part that can be seen in the attached drawing (highlighted in yellow). However, my carburetor seems to be slightly different anyway, because my two choke rods are one connected piece, while those in the illustration are connected with small plastic brackets (highlighted in red). I'm not sure what the function of yellow part is, and since it wasn't present on my carburetor anyway, I would just leave it out. Does this makes sense?

Thanks,
Julius

[newday777]

Welcome aboard the forum Julius
First off, you have Keihin PD46A carburators,  not Keyster carburators.
You bought Keyster carburator rebuild kits correct?
You can use the gaskets from the kits.
Don't use the brass parts from the kits. Aftermarket brass are not machined to the same tolerances and standards as Keihin did.
Just clean the stock jets and reuse them.

[Julius]

@newday777: absolutely, it's a Keihin carburator but the replacement kit was manufactured by Keyster. Sorry for the confusion. Some of the brass parts have shown some damage so I replaced them with the parts from the kit, I was only hesitant to do so with regard to the emulsion tube because of the different hole pattern so I used the old one (which still was in good shape). Many thanks for your reply!

[newday777]

Aftermarket brass parts not manufactured in the same tolerances and specs as Keihin did. You will be fighting a hard battle to get it running properly.

[bryanj]

You must fit the small w.asher and O ring on the mixture screw properly and DO NOT tighten too much or the tiny metering pin and hole will be distorted, aslso ensure old O ring is out.

Pilot jets are pressed in but need to be removed and cleaned

[Julius]

Thanks for all your advice, which is really helpful (it's my first motorbike restoration project). I have very carefully red everything I could find and also stumbled across the issue that many folks forget to get the washer and o-ring out of the mixture screw hole. That's all done and all the small canals are completely clean. I will use the old and original Keihin brass parts then, they seem to still do the job.

As mentioned in my first post, I will change the screws to stainless steel allen screws (but not for those screws with contact to aluminium). I guess there is no reason not to do so?

[Deltarider]

[...]
Third question: My carburetor was missing the part that can be seen in the attached drawing (highlighted in yellow). However, my carburetor seems to be slightly different anyway, because my two choke rods are one connected piece, while those in the illustration are connected with small plastic brackets (highlighted in red). I'm not sure what the function of yellow part is, and since it wasn't present on my carburetor anyway, I would just leave it out. Does this makes sense?

Thanks,
Julius

Julius, I don't know where you live, but many questions about these PD46 carbs can be answered by studying thoroughly the CB500K3/CB550K3/CB550K4 part list. It has no less than 8 pages about these carbs...  Use this edition: https://www.honda4fun.com/dwnload/Part-List/CB500/CB500-K3-CB550-K3-K4-Parts-List.pdf The one in the UK site is not complete.

[Julius]

Thanks, I have actually very intensively studied this part list. The drawing of the carb in that part list is the same as that one which I included in my first post. However, my carb is different in some respect. For example, the choke rod does not have these plastic connectors (highlighted in red in the drawing attached to my first post). Instead it is the same like the one used in this PD42A http://forums.sohc4.net/index.php?topic=146893.0. In fact I have not yet found a drawing that shows exactly the version of my PD46A. I guess, however, I am just a bit to scientific. I will finish the carb and see if everything works as it should.

 I live in Munich, by the way.

[newday777]

Thanks, I have actually very intensively studied this part list. The drawing of the carb in that part list is the same as that one which I included in my first post. However, my carb is different in some respect. For example, the choke rod does not have these plastic connectors (highlighted in red in the drawing attached to my first post). Instead it is the same like the one used in this PD42A http://forums.sohc4.net/index.php?topic=146893.0. In fact I have not yet found a drawing that shows exactly the version of my PD46A. I guess, however, I am just a bit to scientific. I will finish the carb and see if everything works as it should.

 I live in Munich, by the way.

Do you know that the PD42A  is for the 78 CB750F3?

[Julius]

I was just referring to that PD42A rebuild post because this particular carb has aparently the same choke rod like my PD46A. The choke rods shown on the drawings of the CB 550K3 carbs are different because they have those plastic connectors. I have attached a picture showing the parts of my PD46A for reference.

[HondaMan]

I have used non-OEM screws and split washers on the choke plates on occasion, also including Loctite thread locker, but I first split the tips of the screws with a thin Dremel-style moto-tool grinder wheel so the ends could be slightly spread - much like Keihin's special hollow-point screws. I used a small v-block of steel I fabricated as the wedge, and some small lock-type pliers for the force. They spread the screw tips only a small amount, but this prevents them from turning and lets them be ground off if necessary to remove them again.

[Julius]

Great, thanks for your comments. I will do the same hoping that it will last for some years.