Topic: 1977 CB500K3 carburator questions

[Malovski]

Hello everyone!

Two weeks ago I became the proud owner of my first ever motorcycle, a 1977 CB500 K3. The bike is in a bit of a rough shape (but nothing serious) and will need some work to bring back its former glory! I have since I bought it spent hours and hours reading on this forum, trying to obtain as much knowledge as possible. Some questions have however come up that I have not been able to find any answers for. At least not so that I understood it.

My first question came up as soon as I opened up the float bowls to evaluate their condition and see what I need to buy before rebuilding them. What struck me was that three out of the four floats are BENT?! One of them also have some slight damage done to it. Can this be fixed by bending them straight again, or should I just buy new floats? Also, any idea why whey are bent? Other than that all the brass in the carbs looks to be in very good nick, but all the gaskets needs replacing.

Pictures of the Carbs/floats: http://sv.tinypic.com/a/fkxk6t/3

My second question is straight up if the carburetors that is on the my bike are the correct ones, or from a earlier Cb500? What makes me ask this is that when I go on Davidsilver/Ebay/4into1 the top gasket for the carburetor ”lid” that is listed to fit my 1977 Cb500 isn’t the ones that is on, and will fit, my carburetors. I instead have the ones found in the kits for the 1976 Cb500 and bellow! I also doesn't have the vacuum port screws in the inlet manifolds if that matter. I googled my way to this thread http://forums.sohc4.net/index.php?topic=85743.0 and for me it looks like I have the same situation, that is to say that I have inlet manifolds for PD carbs but earlier 022a carburetors (not that I know the difference between them). Feel free to remark me if I’ve gotten anything back-ways!

Pictures:

The carburetor lid gasket said to fit my bike:
https://www.davidsilverspares.co.uk/graphics/parts/16010393305P_large.jpg

The gasket type that fits/is on:
https://www.ebay.co.uk/itm/Carb-Rebuild-Kit-Carburettor-Repair-Kits-for-Honda-CB500F-CB500-F-Four-CB-500-HH/382483998668?hash=item590dd2a7cc:g:35gAAOSwM9RbGKus:rk:11:pf:0

Thankfull for any help!
Cheers,
Max.

[Yamahawk]

Looks like someone replaced your carbs with an earlier set. The floats may appear to be bent, but I think that is stock, as sometimes they have an off kilter look to them. The ones with the 'keyhole' gasket are also used on the Cb550's of that year.
Charlie

[calj737]

The floats may be hanging crooked due to how they’re affixed to the main jet. There’s a larger hole that fits over the jet, then a slot for holding them in place, and then two guides to rotate onto the post for keeping them. Not uncommon for the floats to become wonky after some rattling around.

Look at the outside of the #4 carb, engine side of the carb, there’s an ID # stamped into the flange. That will tell you exactly which model carb you have and the proper components for it. If you have the incorrect intake manifolds, you can drill a vacuum port into them. 5mm tapped hole is the result you want. You can get some 5mmx6 screws and cut them to length so they don’t protrude too far into the intake manifold. A rubber o-ring beneath the screw is advised.

Looks like you have pods on that bike. Will make tuning more of a chore. Beneath the main jet, is the emulsion tube. If you lift the throttle slides fully, you can sometimes remove that with a small wooden toothpick or similar. They push in from below. You’ll need those to be spotlessly clean.

[Deltarider]

Malovski, welcome here. Your K3 is one of the rare CB500K3s (around 4000 assembled). Your first step should be to determine what manual and what parts list is appropiate for your model. This is the genuine Honda parts list: http://www.honda4fun.com/pdf_parts_list/pdf_spac500-550/CB500-550_K3-K4.pdf On p.4 you'll find your model listed and what carbs originally it had fitted. You can check the carb number on yours with the number listed. The pic below shows you where to find the number on your carb (yours originally had PD46B however). Let us know if you happen to have the oldstyle carbs that were on earlier CB500s. The good thing of forsaid parts list is that you will also immediately see what parts your model shares with the CB550K3, a model that was sold in the tens of thousands. You'll find the original Honda Shop manual CB500 - CB550 here (scroll down): http://forums.sohc4.net/index.php/topic,17788.0.html. In particular Part 10 from p. 173 on is important for you: https://www.classiccycles.org/media//DIR_1653304/DIR_1653404/DIR_1653507/ecc6759db0a214d5ffff8825ffffe41e.pdf. BTW, unfortunately p.8 of forsaid manual is missing. I attached it below.
Aftermarket manuals like Clymer and Haynes are incomplete and consulting them can lead to errors. That's probably the cause of your bend floats and wrong parts. Somebody must have drawn the wrong conclusions from the wrong data. I mean, 14,5 or 22 mm float height makes quite a difference...
To complete: a copy of the Owner's Manual you can download here: http://www.honda4fun.com/materiale-documentazione-tecnica/libretti-uso-a-manutenzione To avoid you pick the wrong one, here's the link for the first part: http://www.honda4fun.com/pdf_libretti/500/CB500_550/CB500_550_01.pdf Success in getting familiar with your bike and we are here to help you.

[Malovski]

Thanks for all the feedback, the mystery has been solved! 

I first checked the carbs for serial numbers. They read "649A". A quick search later got me this info (along with alot more):

"CB500s in Europe (France and UK excepted) had 649A carbs that were jetted differently.
We have the same slow jet #40, main jet is #78 and airscrew is recommended 1 turn out +/- 1/8. But these models have a cover over the airfilterbox as shown below."

As I live in Sweden this makes total sense, and also, the reason for me not finding the right carb rebuilding kits was of course, as quoted above, that neither the UK nor the United States ever had these carbs on their bikes. I guess that you Deltarider thought I had another type of CB500K3? Because there surely must have been more than 4000 european K3's produced? Or are they really that rare?

As for the vacuum ports I haven't yet been able to conclude if my 649A carbs does have them situated inside of the carburators as the PD's have, but if they don't, then I will follow your advise calj737 and drill a vacuum port into them. I do however suspect that the 649A's does have a vacuum port hidden somewhere, because why would a PO swap out the manifolds to a pair that would'nt alow for carb syncing .

Lastly, I've dubble-checked and, to me, it does really look like the floats have been manually bent out of shape. As you said Deltarider I suspect that it has to do with a PO who has been tampering with them. The carbs also do have 95 main jets in them rather than the size 78 ones. I'm planning on going back to a factory airbox (I have found one which seems to be complete for 40€) so I'll have to think about what jets to put in after the rebuild (the bike also has a aftermarket 4-1 system). But that is a later problem  .

Thoughts on a carb kit like this?
https://www.ebay.co.uk/itm/Carb-Rebuild-Kit-Carburettor-Repair-Kits-for-Honda-CB500F-CB500-F-Four-CB-500-HH/382483998668?hash=item590dd2a7cc:g:35gAAOSwM9RbGKus:rk:11:pf:0

I am a student so so I'd rather avoid paying around 80€ or more for a genuine rebuild kit. Alternatively I've considered finding the individual sizes of o-rings (have seen them mentioned in the forum) and buy them from a o-ring-retailer aswell as making the top gasket myself, but it would be alot more work than just buying a 4 kits from ebay...

[Deltarider]

So... yours is a K3 that had the original PD carbs replaced by earlier oldstyle carbs?? The CB500, CB500K1 and CB500K2 had little screws in the intake manifold. That's where you can screw in the adapters for syncing (encircled red in the pic). Normally these bikes do not need syncing unless they're 'played' with.
That set offered in Ebay has an incredible low price and must be imitation. The seller 'Honghong' seems to be in China... I don't have experience with aftermarket products, but people here complain a lot about aftermarket. BTW, what makes you think you need new? My experience is the original brassware hardly wears if at all. That's no wonder, if you realise how little gas has passed it, the bike being only 500cc and then having no less than four carbs... So far I haven't had to renew one of these items in 140.000 kms... rubber seals, yes, a few (around the main jets), but no jets, no needles.

[bryanj]

The 500K3 is a rare beast even in europe and was never imported officially into the US or the UK. It is basically a 550K3 with 500 barrells and pistons. The PD carbs are notorious for being a swine to work on and keep clean internaly and were designed so the engine could run lean for certain US states. They were so temperamental that if the bike stood on the showroom floor for over a month you could just about guarantee having to remove and clean them. The bent floats could be because somebody tried to set early carbs to PD settings which are a lot different

[Malovski]

Deltarider, as I have come to understand (I may be wrong), these cb500's k3's, mine included, who were sold here in Scandinavia never recieved the PD carbs from the factory, but instead the "old style" 649A carbs? Or have I gotten it wrong? As for the cheap knock-off rebuild kit's I am totally with you on that the original brassware are completely fine, I just need new gaskets and for the 5€ the cheap kit cost, my idea was/is to buy them just to use the gasket/o-rings but keep the original jets etc. It would still be cheaper than buying gasket kits from say DavidSilverspares, who charges 12€/piece for a aftermarket gasket set or 25€/piece for an oem one (which I think is too expensive for just a couple of orings + a gasket).

Fun to hear that the Cb500k3's are so rare! Just so I've understood everything correctly however; my 649A carbs, those arent "PD" style carbs are they? But "old style" ones? I'm not really familiar to the terms yet namely...

[calj737]

Correct on all accounts.

[Deltarider]

Correct on all accounts.

Calj is mistaken. The CB500K3 originally did have the PD carbs  A quick glance at the appropiate Parts List could have told you. These were the same PD carbs the CB550K3/4 had, be it with a slightly different jetting. See the Honda Shop Manual from p. 173 on for the details. Malovski, have you verified by comparing the engine- and framenumber, yours is a K3? Anyway, don't worry your bike doesn't have the original PDcarbs. Consider yourself lucky you have the oldstyle Keihins instead. I have the 649A carbs as well on my CB500K2 (ED), first registered in 1977 (!) that I own since 1980. The oldstyle carbs are easy to work on if needed (mostly not). I can guide you with the do's and dont's. The CB500K3 with the original mufflers was the sweetest running of the whole CB500/550 range and had almost no vibrations, the reason I'd prefer it over the CB550K3. Does yours look like this or the second pic?

[Malovski]

Okay now I get it! Sorry if I came cross as ignorant, I should have looked at the parts-list more carefully. The bike looks like the one on the first picture, even if a previous owner has tried to imitate a Cb500 supersport by respraying it and mounting a 4-1 exhaust. I've compared the serial numbers on the engine/frame to the parts list and they both match.

Here's a photo of the jewel, now that I've learned how to post photos 
My to-do list as for now:
*New correct front fender
*New seat cover
*Clubman bars
*Carb cleaning
*Find an airbox
*Fix any rustspots on the frame
*New smaller turn-signals
*Either a repaint or a new tank as the current one has started to rust on the outside next to the frame mounts.
*New fork seals
*New dampening in the silencer
*Overall service with oil,plugs etc
*New gear shaft oil seal
*Maybe some performance mods a'la "The thoughts of Hondaman"

[Deltarider]

Your bike is a K3 with the 649A carbs that were on the earlier model CB500K2 (ED or G). Congrats, these carbs are troublefree compared to the PDcarbs with their horrible slow jets that always get clogged up if you don't ride regularly. The 649A are also much easier to work on and they should do fine on your bike as the engine is 100% identical to the older models.
Now that you have the carbs out, this is is what I'd do. Excuse me, a "Don't' first. Don't separate the carbs from the rack. It is NEVER needed, not ever, NEVER!
Looking at your pics, I don't see why the floats couldn't be reused after being readjusted. Check for the correct procedure p. 60  in the Honda Shop Manual CB500 - CB55O. You can make a 22mm gauge yourself easily (see pic). First check if the floats can move freely on their swivel pin. If not, remove swivel pins and polish them lightly and spray with a little WD-40. If you need pliers to extract the swivel pins, do it very carefully! Some manage to break the towers, so do it gently and don't pinch the ends! Study the floats brass. The little adjustable tang in the middle should run parallel with the rest of what it is cut out. Inspect the float needles and maybe polish very lightly the tip (top) that shuts and opens the valve. A bit of WD-40 is probably enough. Inspect the O-ring around the valve. Remove the main jets and inspect their little O-rings are still in good condition and will seal well. Screw out the slow jets (gentle!) and see if they're open. Use carb cleaner and only stranded copper wire as seen in the pic below. Don't be tempted to use materials harder than the brass. You will damage your jets. When in doubt, order new original ones, they're not expensive.
I trust you still have the carbs in the rack. Again, don't separate them from each other! There's no need to, ever, no matter how many manuals show you how to do it! Ignore them! Now with one hand, imitate full throttle by raising all 4 slides. If the needle jets (aka emulsion tubes) don't come falling out by themselves now, you can help by inserting a little wooden toothpick or whatever from below and pry them out. A bit of WD-40 at forehand can help. Inspect the needle jets and check their little holes in the sides are open. BTW, don't bother to open the top lids of the carbs, There's no need to go there. In other words: leave the needles where they are (that is: for the time being). Unscrew the airscrews in the side of each carb after you've took note of what position they were at (how many turns out). Don't loose their little springs. Now you can spray carb cleaner in/through each of the 4 holes that consist the idle (aka pilot or slow) circuit of each carb:
1. the orifice where the slow jet sat,
2. where the airscrew sat,
3 The little orifice in the intake of the carbmouth ('Pilot system air jet' in the pic)
4 the tiny little hole just in front of the carbslides (engine side)
By using a straw on your carbcleaner can and by - in turn - closing each orifice, you can check the passages are clear.

[Malovski]

Thank you for putting in the time and effort to educate me on how to do this properly! I will certainly follow your advise to make the 22mm guage.

HOWEVER, make sure you're sitting down now, I just might have dissasembled the whole rack yesterday... To my defence, I was following the Honda service manual on carb dissasemble...

The thing is also that even if your carb-cleaning method most certainly will make the carbs work like they were new, I also want to make them look like new on the outside. This (I thought) would be inpossible without taking it all apart. My plan has therefore been to completely dissasemble the carb-rack (SORRY!!) and submerge them into a swedish equivalent to simple green, followed by a thorough rinse in hot water,  pressurised air blown into every hole and lastly a coat in WD40 to keep any corrosion/flashrust away. Do you think this would be a bad idea?

To put some perspective on it, here is how dirty the carbs/rack were AFTER I already had blasted their outsides with a toothbrush and brakecleaner, this is really not something that I would want to install back on the bike:




Now this is the rack after going through "my" treatment yesterday. Just imagine yourself all the carbs in the same condition


Again THANKS for going through the trouble of helping me, I greatly appreciate it and will absolutely follow your advice in how to inspect the insides of the carbs.
Max.

[Deltarider]

Every CB500 will eventually leak some oil near the head gasket. Nothing serious, it is not even the headgasket that is leaking. Mine has been sweating ever since I bought the bike in 1980 and with two intervals after renewing the head gasket, guess what, it is sweating as before. It has to do with the little O-rings around the oil passages and their shrinking during hibernations. So IMO cleaning the outside of the carbs is useless. They will get dirty again, combination of the oil flying from the engine and the dirt/dust that will swirl around in the vacuum whilst riding. Mine look dirtier than yours before they went into the bath, but inside they're spotless. It's the nature of the beast, I'm afraid. In all those years my bike gave me very little trouble and practically all issues had to do with standing, not with riding...
Although I advise you to leave the carbslide needles alone (back then nobody would go there, where in this forum... ). Anyway, if you really must, make sure you use a proper JIS screwdriver to free the 3mm screws in there. When you use a Phillips, you will most probably ruin their heads and then it will be very difficult to get them out.
As for manuals, ofcourse Honda had to describe every dissassembly imaginable, because Honda could not foresee what problems would occur. Experienced mechanics later however knew, after seeing hundreds of these bikes in their workshops. They knew from experience which type of bike would likely develop this but never that. Aftermarket manuals like Clymer and Haynes lack that experience, although Haynes here and there warns 'ít would be unlikely...' Mind you, these manuals were put together partly by copy and paste from manuals that had been published before on other bikes (British, Guzzi's, Laverda's, BMWs, you name it). But every bike (or car for that matter) has its own typical faults. Only mecs that worked on these bikes for years, knew what would occur with this or that bike and also what not. The stupid thing is that Honda had much improved on errors other brands had made. Now, the publishers of aftermarket manuals like Clymer and Haynes will gladly fill their pages with what they had already published before in their books on other bikes. Paper and ink are cheap and the thicker the manual, well the more succesful, because adspirant buyers will think they'll get 'value for money'. That is the reason you will find so many things described in these manuals that occur very rarely in the life of a Honda. But these things are still in their books in full and lots of people think: hey, this refers to me. Alas, this often leads to unnecessary 'repairs', 'overhauls' and what not. The messing with the floattangs is a just an illustration of this phenomenon. Very sad. I myself have never encountered a CB500 or 550 that needed their floats to be adjusted.

[calj737]

Malovski - be careful with the solution you soak the carb bodies in. The carb is an alloy and many solutions have an aggressive pH and other potential caustic elements that will damage, not clean, the carb.

With the body apart, you can use a toothbrush and scrub with elbow grease more effectively than a risky solution. If you can locate a friend with an ultrasonic cleaner, a 5 minute bath in that works extremely well.

[Malovski]

Okay, it would be foolish of me not to take your advices.There is no need for me to disassemble the carbs further when they actually are'nt that dirty. I will therefore first scrub the carburetors with a bit of good ol' elbow grease as you suggest calj737 and then, when I have new gaskets, follow your advise Deltarider on how to clean/inspect the carbs. If I come across any problems on the way I'll post a question here.
Cheers!

[Deltarider]

Succes and keep us informed! BTW, the other day I've posted some links, including one to the original Owner's Manual. Allow me to make two comments that may be off topic here, but anyway... When checking the tappets, ignore Honda's method. Less chance you make a mistake if you do one cylinder's IN and EX valve at a time. More serious is the method Honda describes in this booklet to adjust the camchain tensioner. It is wrong. I don't know why it is there and I suspect a bad 'çopy and paste'.. You run the risk of never getting the tensioner right that way. BTW, you will not read to do it like this (with the engine running) in any other CB500/550 Owner's Manual and all models have exactly the same tensioner... Best method is the way described in the CB650 manual, which model happens to share the same tensioner.

[mrhonda1948]

You do have to split the carbs apart to replace the o-rings on the fuel feed tube connectors, which is a good idea after 40 years. It does require extra work to get them all apart, especially with the choke shafts/screws. That's the only way to solve the gas leak problems with shrunken o-rings though.

[Deltarider]

You do have to split the carbs apart to replace the o-rings on the fuel feed tube connectors, which is a good idea after 40 years. It does require extra work to get them all apart, especially with the choke shafts/screws. That's the only way to solve the gas leak problems with shrunken o-rings though.

In spite of the pretty rough treatment by me whenever I had to slide new fuel lines on the nipples, my O-rings at the T-joints still don't leak. Honda did well fitting double O-rings at both sides of those T-joint. I personally try NOT to repair things that are not broken, the more when it's very simple to check they still seal.

[Malovski]

Thanks for the advise! I will be sure to post an update when I have made some progress (or when I have more questions needing answers) . As for the cam chain tensioner, thanks for the warning, I will do it the right way, with the engine off! I would prefer to follow the way described in the correct cb550/500 manuals (eg with motor off and in TDC) over the one described in the CB650 manual as I found that my favorite youtuber had made a "How-to" video on his channel accordingly. I namely like having a video to follow over just a manual, I think it becomes easier to understand the procedure that way.

Btw, when changing brake fluid the other day I noticed a tiny bit of leakage at the lever. Is this something I should look further into or ignore until it (maybe) worsen? The break feels just fine overall. If it's just a o-ring I might aswell fix it before riding season so I can be sure it does not result in having to fix it next summer, when I want to be out riding  .

Here is a photo of the lever, sorry for it being sideways

[bryanj]

If it is leaking arround the steel pin the lever pushes on you will need a complete kit and it will only get worse. Only difficult bit is removing the circlip.

[Malovski]

If it is leaking arround the steel pin the lever pushes on you will need a complete kit and it will only get worse. Only difficult bit is removing the circlip.

Yes I suspect that is where the leak is coming from, have not had the time to check more thorough yet. I have taken my time to read around now and it seems like a fair bit of work to rebuild one. I will do a read up on replacing the master cylinder with one from a more modern bike, or if I buy the aftermarket one that Davidsilver sells for 30€. Should be the best option, I'll see after I have read some more master-cylinder-related threads.

Thanks!

[Deltarider]

... as I found that my favorite youtuber had made a "How-to" video on his channel accordingly...

I would like to see that video. Can you post a link?

[Malovski]

... as I found that my favorite youtuber had made a "How-to" video on his channel accordingly...

I would like to see that video. Can you post a link?

Absolutely:

[Deltarider]

I was afraid of that. Don't do that trick with the flathead screwdriver once the nut is loosened. Bryanj will agree with me. Just loosen the nut and then fasten it. There's no harm in using a flatscrew driver to hold the tensioner bolt (very carefully!) in position while tensioning the nut again, but careful, only for that! And certainly DO NOT pressure it inwards! Therefore, for a start I would forget about the flathead screwdriver. Experienced mechanic Bryanj has warned several times here NOT to have a flathead driver even near it! For a reason, lots of tensioners were messed up this way. Don't ask me how I know.