Topic: PD42A Carb Disassembly/Assembly

[Tanerrx]

Does anyone know where I can get just the o-rings for this part in the picture?

Also, how important are those felt washers?  I destroyed mine.  Wish I would have seen this before I disassembled mine. 

My carbs are from a 1980 CB650C but I'm guessing those fuel joint connectors are the same size.

[DWS]

You can get the felt rings here and other parts also, it took awhile to find this sight.


http://www.motorcyclecarbs.com/BUTTERFLY-SHAFT-SEAL


if it does not work for you just type in:
www.motorcyclecarbs.com
and find the link there.

[futility]

Thanks for all the replies and kind words and I apologize for the long absence. I'm looking into the problem with some of the pictures. If necessary I'll host them somewhere more reliable. I understand this post isn't very helpful without them!

[SKTP]

Thank you — this is in my future

[Darren Jakal]

I wanted to thank the original poster for providing the details for this job and would like to offer something back if I could.

I just finished cleaning up the carbs on a 78 cb550 and unfortunately the choke felts were finished (it's been parked in a back alley in Canada for 20 years).

I was looking for an alternative as these felts seem hard to come by and I've read that o-rings are likely to interfere with the chokes movement.

I was looking through a parts box for something that I could slide over the shaft and push it up against the carb body to make some kind of a seal (not sure how much of a seal the felt provide when new, but nothing seemed pretty bad).

Anyway I came across some brass grommets that I was able to slightly enlarge on the narrow end to fit over the choke shaft. They slide right into the carb body as long as you don't over enlarge them. They seem to provide a not bad seal with no interference of the choke movement.

Now, is this a bad idea?

Cheers, Darren

[sdmsc]

Darren:
Thank you ever so much! I would still be staring at the choke rods and their springs if not for this studious and photo-heavy post.

[Ericcb750]

We cannot thank you enough for taking the time to do this...Seriously. Although I've been through this myself, these carbs can still be a little tricky and this is an awesome write up with great photos....Very much appreciated.

[Yoshimatic]

Thank you for the very detailed repairs. Excellent.

[Johnie]

Subscribed for future reference...thanks!

[Jonm99]

Hi, amazingly helpful thread, thank you! I am in the process of restoring a cb750k 77 and I accidentally stripped one of the screws in the carb arm set link (the one that bolts it to the cam). I can't seem to find any replacement for this screw other than purchasing the entire arm set? Does anyone have a link or part number for this screw?

Thanks again,
Jonathan

[flybox1]

Hi, amazingly helpful thread, thank you! I am in the process of restoring a cb750k 77 and I accidentally stripped one of the screws in the carb arm set link (the one that bolts it to the cam). I can't seem to find any replacement for this screw other than purchasing the entire arm set? Does anyone have a link or part number for this screw?

Thanks again,
Jonathan

How about measuring its length, width and TP....and then buying one at a hardware store  (or cut a longer one down to the same length)
If you want to be more exact with it....boltdepot.com

[Jonm99]

How about measuring its length, width and TP....and then buying one at a hardware store  (or cut a longer one down to the same length)
If you want to be more exact with it....boltdepot.com

LOL, and then there is the practical approach... Thanks for the link Flybox, that'll do it

[akranem]

one of the best PD's carb break down ever seen on the internet.....thank you for the risk you took, learned alot without jumping into it with out some kind of reference......im going to just #$%*ing do it now, got an extra set of carbs might as well try right?

[Erny]

This is really great thread!
First time I found such comprehesive and detailed procudure for PD carbs

I plan to clean mine PD41A (CB750 K7) as I have issues with idling (suspect clogged slowjet passages and issue with accel pump)
Will decide when I inspect if I break them apart or not.

Many thanks again!

[goodtryer]

I'm in the middle of this rebuild process and wanted a printed copy of this procedure to work from. So I made a PDF of the page and thought it might be useful to others.

All credit to the original author. Thanks for a great post!

Cheers

PS: In order to get the file down to an acceptable size for upload, I had to split it into 2 pieces and make it compatible only with Adobe Acrobat 10 or later. If I went to version 9 or earlier, it grew to 74MB.

[jayrdee]

+1 on the awesome write up. I just finished putting together my PD41 (77 CB750K) carbs and this was a great reference.

Although I do have a question for you veterans out there (I'm a young guy and this bike is my first one, like ever) ...

After tightening the rear stay plate, my choke valves only close about 65-70% of the way using the linkage, and you have to force them to go any further. When I take all 8 screws out of the stay plate, the valves close 100% using the linkage. Seems like there's a bind somewhere when I tighten everything up.

Has anyone else ran into this problem?  Or should I just roll with it? I would imagine its not that big of a deal since its just the choke assembly. The main throttle valve assembly opens/closes just fine, which thats the important part.

Disregard. I'm a dumb@$$ and didn't notice the linkage catching on the adjustment screw. Literally talks about how to adjust it on the following page, after how to sync the carbs in the service manual 

[Flyin900]

Just my 2cents!

Good detailed write up and if your fortunate enough to be able to only clean the jets and carb bodies while still assembled it is a better way to go.
Having cleaned many sets over the past 12 years unfortunately the only option is to break them down as this poster did if your using aggressive cleaners. The 40 year old fuel rail and accelerator pump rail O rings are likely to leak for sure, given most people are inexperienced. The use of an aggressive carb dunk/carb spray cleaner will destroy rubber O rings on these rails and the old felt seals.
Also, if the carb set uses air cut valves which many do, it is almost impossible to access the 3 inner ones with the bank still assembled. If you use a carb dunk with those still attached it will destroy the diaphragms and small D ring seal in there for sure.

The felt seal can be found at Mike Nixon’s website motorcycleproject.com ( an excellent resource site and ex Honda and Kawasaki tech) and at dudesgarage.com

[Erny]

Gents

don't want to to create new thread so will ask here.

Preparing for long time postponing cleaning of my K7 carbs, including removal and cleaning idle jet (one that is pressed in)

Before starting the work I'm trying to collect methods how to remove safely idle jets.
Sofar, I found methods to protect jet (hose etc) and using pliers/grips do twist/pull to remove it in combination using some penetration oil before..

Any other method proven to work? I was thinking about using some heat?

Thanks for any proven methods, I'm quite afraid not to damage carbs

[70CB750]

Gents

don't want to to create new thread so will ask here.

Preparing for long time postponing cleaning of my K7 carbs, including removal and cleaning idle jet (one that is pressed in)

Before starting the work I'm trying to collect methods how to remove safely idle jets.
Sofar, I found methods to protect jet (hose etc) and using pliers/grips do twist/pull to remove it in combination using some penetration oil before..

Any other method proven to work? I was thinking about using some heat?

Thanks for any proven methods, I'm quite afraid not to damage carbs

I just done it few days ago.  I used a piece of tygon fuel hose that fits over the jet easily and a pair of pliers.  Firm grip and light twist from side to side is all it needed.
I could not fit vice grips over it so I used these.

[Erny]

Thanks! So, hope this method will work in my case too

[cspark901]

I have just put these carbs back together and the needle inside the slide is loose after i tightened the two screws inside the slide. I cant remember is this was solid or loose when i disassembled. Is that correct or are the needles supposed to be solid?

[wildxcard]

In futility’s original post, Section: “Tearing down the carbs” step 11, he addresses removing the throttle shaft seals, “On carbs #1 and #4 these seals are felt. On #2 and #3 they are rubber.” Despite the right tools for the job, my seals were in bad shape and I struggled with these steps, damaging many of my seals.

Thanks to Mike at https://www.motorcycleproject.com/ I think I have the felt seals tracked down but when attempting to remove the rubber seals, they crumbled like brittle old plastic, (see pic).

I have searched and searched for replacements as well as OEM specs (size and composition), but have not had any luck. Does anyone have any suggestions here?

I’m basically at the point where I’m looking at used 77-78 CF750F carb banks on ebay in the hope that I might be able to salvage the seals.

Reproductions would be ideal, but specs on size and composition (type of rubber, plastic, etc…) as well as any suggestions on any recommended vendors would be so so appreciated.

[bryanj]

 I have a bank of pd's off a 550K3 so i will see if the are any more identifyable for you later

[EWFrith]

Wow, this is a gold mine. Thanks for the meticulous write-up, Futility.

I need to this on my '77 f. She gets about 15mpg and spits black smoke out the back like a steam engine. I have practically zero wrenching experience, so I'll be second-guessing myself all along the way. How long did this job take you, and how long would you guess it'll take me? Hours, days?

Thanks again.

Eric

[goodtryer]

It’ll take days.

BE METICULOUS!

Take a thousand pictures before you turn one screw. Take them from every single angle. Take a bunch and then take some more. Take pictures after every step. The hardest part for me was the return springs on the choke. Even though I had a picture, it wasn’t great and I had a hard time getting things lined up.

Have containers and ziplock bags and tape and a pen. Label everything and carefully keep things organized.

Do not throw away any old pieces. Until a year from now when you’ve gotten everything back together and the bike has been running for a while.

There are some little (tiny) brass restrictors in the hoses between the carbs. If the hose are bad you’ll have to cut open the old hoses to get the restrictors out so you can put them in the replacement hoses.

You’re going to need the felt seals and the rubber seals that go on the rods between the carbs. Get these before you do the tear down. It’s much better to have all the replacement parts on hand   That way you don’t have things apart for days waiting and forgetting.

Finally, test the movement of things as you rebuild. The choke on mine had a slight stickiness to it thought I stupidly thought would work itself out after being I use for a while. It didn’t and I had to take the carbs off again and refit the choke plates. The one in #3 was misaligned and caused the sticking. Speaking of those plates, you’ll want to have blue Loc-tite on hand for those screws. Don’t want those coming out and going into the engine.

Finally finally (I keep thinking of more things). I got a set of carb cleaning wires and brushes off Amazon that were really handy for this project. They were only a few bucks and I’ve used them on several other things since then.

Cheers