Author Topic: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning  (Read 7349 times)

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Offline vulture0027@gmail.com

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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #25 on: March 04, 2019, 09:26:33 PM »
Sorry to beat this thread into the ground...
BUT.... how long do you think it should take for gas to stop running from the overflow tubes at the bottom of the carb bowl? It’s been about 48 hours since I put the carbs back into the bike. This thing just keeps wanting to leak gas from the overflow tubes. Just now went to the gas station. I got there, turned off the bike and after a few seconds gas was flowing pretty good from carb 4, then stopped, then started draining from carb 3, then started dribbling from carb 2 then 1. By the time I left the gas station there was a puddle of gas about a foot and a half in diameter. Is this normal?

Offline bryanj

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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #26 on: March 05, 2019, 01:35:23 AM »
ALWAYS turn the petcock off when you stop the engine but having said that you still have a problem with either float neddle valves or standpipes
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Offline Deltarider

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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #27 on: March 05, 2019, 03:27:47 AM »
White smoke can indicate condens, usually generated by short rides where the engine did not reach its working temperature or water in the fuel.
First you have to be sure where the fuel comes from. Is it really coming out of the tubes or from somewhere above and then running down the carb bodies?
If from the pipes, here's a couple of questions:
Do you have the genuine Honda (Keihin) valve seats and needles?
You didn't use anything abbrasive cleaning them, did you?
Did you mess with the floattangs?
Did you fit the float seats with their O-rings snug and the valve needles with their pyramidlike tip ^ up?
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Offline nuwonder

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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #28 on: March 05, 2019, 05:07:02 AM »
Some floats can also be installed upside down, which would probably cause serious overflow as the tang wouldn't make the needle valve close at all.
Sure you put floats back as they were?


Offline vulture0027@gmail.com

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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #29 on: March 05, 2019, 09:37:38 PM »
Bryanj: sometimes I would forget to shut off the petcock and a little gas would leak from one of the carbs, but not like this... now there is a steady stream. Not sure what a standpipe is. I googled it and the front forks came up. Are you talking about the brass tubes that are at the bottom of the float bowls?

Deltarider: definitely didn’t mess with tangs (if you meant did I bend them ... then, no I didn’t)... I did however pull off the swivel pins to clean them with carb cleaner. Didn’t use anything abrasive to clean ANYTHING. I used one of those fuzzy pipe cleaners to clean the “hinges” where there the float pins insert. If the picture that is attached is what you mean by “float seats and valve needles”, I didn’t remove the valve seats. I only removed and cleaned the pyramid-like tip or each carb (put them in face up - towards me) Not sure what kind of valve seats/ needles are in there, I didn’t replace them, I only cleaned the pyramid- like tips.

Nuwonder: (as I recall, the floats that are in my bike are rounded on both the top and bottom... I think put them back the way I took them out, but now that you say that, I’m second guessing myself... kinda like when I leave the house and get to work then I think to myself “did I lock the lock the door?”

One thing I DID notice was that when I had everything put back into (what I THOUGHT was the right place), there was a VERY SLIGHT resistance getting the float bowls back on to the carb body. There was about less than a 1/16 of an inch gap at some points in between the float bowls and the carb bodies... I thought that the float bowls might be pushing on the leaf springs that sit over the floats (problem there?). I’m guessing I’m going to have to take the carbs out again to investigate, right? Should I just buy this gasket/o rings kit to play it safe?

Offline Deltarider

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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #30 on: March 06, 2019, 12:43:35 AM »
Not sure what kind of valve seats/ needles are in there, I didn’t replace them, I only cleaned the pyramid- like tips.
Theoretically the O-rings around the valve seats could leak or there's still some dirt in the seats holes that prevent the needle tips to shut off the flow completely. You can use a Q-tip with some carbcleaner or WD-40 to clean those holes.
Quote
One thing I DID notice was that when I had everything put back into (what I THOUGHT was the right place), there was a VERY SLIGHT resistance getting the float bowls back on to the carb body. There was about less than a 1/16 of an inch gap at some points in between the float bowls and the carb bodies... I thought that the float bowls might be pushing on the leaf springs that sit over the floats (problem there?). I
No, it's normal to feel that resistance and you're right in your assumption.
Quote
Should I just buy this gasket/o rings kit to play it safe?
I can't tell from here.
Don't despair. There must be a simple explanation for your problem. It seems to me you did the right checks. Just go over the list of what we suggested once more.
« Last Edit: March 06, 2019, 12:48:58 AM by Deltarider »
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Offline bryanj

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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #31 on: March 06, 2019, 02:39:31 AM »
Standpipes i meant are the brass tubes inside the float bowls which can crack an allow gas to come out of the little pin on the outside at the bottom.
Floats, if you look at the tang that sits on the pin of the needle(which should be sprung loaded-- meaning you can push the pin in a bit and it springs back) the tang is normall bent a small amount towards the pin, also if i remember correctly there is a small bet piece on the float arm close to the pivot poit to stop the float moving too far and if you install upside down it more or less stops the float moving.
In the past i have had the pipe from petcock to carbs split at carb end and gas pour down the carbs making it seem that they are overflowing, if so use only the proper black 5.5mm id pipe NOT the clear crap, with or without reinforcing!
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Offline vulture0027@gmail.com

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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #32 on: March 09, 2019, 01:34:40 AM »
Removed the carbs again...

Here’s what I saw in carb #4 (pictured)

The float in this carb doesn’t seem stuck AT ALL.

I will say that the main jet no.100 sits kinda loose... the o ring that I got from my local bike shop seals the main jet, but there is still quite a bit of wiggle room in it... is that a problem (as far as the bike “gushing” out gas)?
Also: I put the main jet 100 in the position shown in the pic ... is this the right way? Or should it flipped the other way?

Offline Deltarider

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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #33 on: March 09, 2019, 04:23:40 AM »
The float in this carb doesn’t seem stuck AT ALL.
Good. The little floattang looks OK. The minuscule (springloaded) pin of the floatneedle is supposed to sit on that tang (the side not shown in the pic).
Quote
I will say that the main jet no.100 sits kinda loose... the o ring that I got from my local bike shop seals the main jet, but there is still quite a bit of wiggle room in it... is that a problem (as far as the bike “gushing” out gas)?
No, a bit of wiggle room is normal as long as it seals well. Not sealing has nothing to do with gushing out gas. The seal is there to prevent the cylinder suck in extra unmetered gas.
Quote
Also: I put the main jet 100 in the position shown in the pic ... is this the right way?
I think you're OK. The hole that is shaped conical goes up. Easy to remember: its conical form is to accommodate the tip of the needle above it.
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Offline vulture0027@gmail.com

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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #34 on: March 09, 2019, 11:56:02 PM »
Here a pic of carbs 1-3... just took off the float bowls and snapped a pic with out touching anything (other than the floats to see if they were stuck)....

Can anyone see anything wrong with how this is set up? Any glaring problems here that would cause gas to continuously drain from the over flow tubes? Lemme know if there is any other angles I can take a pic from that might help.

Offline vulture0027@gmail.com

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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #35 on: March 10, 2019, 01:13:59 AM »
I watched some videos on YouTube about how carburetors and floats work... I THINK I have a better understanding...
 When I turn the carbs in the “upright position” (pictured), the conical needles (valve seats?) dont drop down on carb #2 and #3.... this is a problem, right? Is this the reason for the overflow?... if so, how can this be corrected?

Offline Deltarider

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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #36 on: March 10, 2019, 06:14:02 AM »
I watched some videos on YouTube about how carburetors and floats work... I THINK I have a better understanding...
 When I turn the carbs in the “upright position” (pictured), the conical needles (valve seats?) dont drop down on carb #2 and #3.... this is a problem, right? Is this the reason for the overflow?... if so, how can this be corrected?
I'm afraid not, but I am not 100% sure I understand what you mean. In the normal (upright) position the valve needle rests with its tiny springloaded pin end on the little floattang at ALL times. The float moves up and down with the fuellevel, because that's what floats do. When the fuellevel rises, the float goes up, pushing the floatneedle up forcing its conical tip into the valve above it to shut off the fuel supply. The valve has exactly the same shape as the needles tip 'in the negative' so to speak. Normally the tip shuts off perfectly and the fuelflow stops until the float drops again. Ofcourse the floatneedle is supposed to go down with it. Sometimes however the floatneedle sticks and keeps hanging up there in the valve but that will not cause overflow but quite the opposite: it will prevent fuelflow and so starve the floatbowl. Let me say that, now that you have the carbs 'dry', it's not unusual that you sometimes see the needle stick. This is because there's no pressure exercised by fuel coming down.
Now that you have the carbs removed, you could test with your finger, by moving the float up and down, to verify if the floatvalve really closes. It will be a bit messy because you would need fuelsupply.
But before that. Have you inspected the brass overflow pipes in the floatbowls for cracks/leaks yet? If not, do so first. It's very simple to do. Now that you have the bowls of, fill them with gas or a similar fluid and watch.
« Last Edit: March 10, 2019, 06:32:04 AM by Deltarider »
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Offline vulture0027@gmail.com

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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #37 on: March 11, 2019, 11:20:28 PM »
Deltarider- thank you for the advice. you explained that very well and i think i get what you said 100%. i DO NOT see any cracks or fractures in the brass overflow tubes. gas isn't leaking from around the tubes, it is streaming from the opening (at the bottom) of the brass tubes.
when you said "Now that you have the bowls off, fill them with gas or a similar fluid and watch"....by "similar fluid" what do you mean? can I flow something else through the carbs? would distilled water work?

Offline Deltarider

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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #38 on: March 12, 2019, 04:50:04 AM »
i DO NOT see any cracks or fractures in the brass overflow tubes.
You informed us what you don't see... 
Quote
gas isn't leaking from around the tubes, it is streaming from the opening (at the bottom) of the brass tubes.
So? It doesn't rule out eventual cracks in the tubes...
Quote
when you said "Now that you have the bowls off, fill them with gas or a similar fluid and watch"....by "similar fluid" what do you mean? can I flow something else through the carbs? would distilled water work?
I was referring to the bowls only. Position bowls (only the bowls) on a table or bench. You need to support them so they mimick the position they have on the bike. I can imagine you don't like to use fuel for this test, so fill them with water and see if the fluid exits from the brass pipes. I am not 100% sure if gas can penetrate where water can't. You could also use WD-40, which is known thinner than water, but you need quite some to fill a bowl. I myself have that quantity stored: I've made it a habit to cut the cans open after they've stopped spraying and collect what's still in there (a lot!) in a jar. This is because I use WD-40 also for other purposes.
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Offline bryanj

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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #39 on: March 12, 2019, 05:13:46 AM »
Gas will leak where water will not, you could use paraffin instead.
If the tube is cracked the gas will still leak from the nipple hole on the outside as it leaks through the crack to the inside of the brass tube
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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #40 on: March 12, 2019, 05:37:29 AM »
.. you could use paraffin instead...
Are you sure you mean paraffin and not naphta, Bryan? The paraffin I have here in a bottle seems way thicker than gas.
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Offline bryanj

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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #41 on: March 12, 2019, 08:31:07 AM »
Naptha to me is a wax, parafin in UK is what can be used in old agricultural spark engines, we also call it Tractor Vapourising Oil.
Meths may work for testing but its more flamable so needs more care!
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Offline vulture0027@gmail.com

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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #42 on: March 12, 2019, 10:07:11 PM »
Deltarider- sorry, I guess I didn’t follow what you were saying at first... I guess I jumped the gun when I used the phrase “I understand 100%”... :/

So... I just used gas. I filled each carb bowl with gas (like you said).... no visible leaks in any of the bowls from the brass overflow tubes. Attached is a pic of how I set up each float bowl with gas.

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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #43 on: March 12, 2019, 10:38:39 PM »
AND... just to reiterate, the valve seat/ conical-like “needle” needs to be in the position shown in the picture, right?

Offline Deltarider

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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #44 on: March 13, 2019, 01:17:28 AM »
No! You've fitted the needles up side down. No wonder it's leaking gas. The pyramide end is supposed to be ^ so it can be a nice fit to close the valve which has a hole also shaped ^ but in the negative so to speak. The other end with its tiny springloaded tip is supposed to rest on the floattang. So congrats! You've found the cause. I hope all the air vents were open at the time and no fuel was spilled into the engine... I would advice you to check the oil, if it smells of gasoline. When in doubt, change the oil!
BTW, now that you have the carbs on the bench with the floats removed, it's a good opportunity to look after a few other things. It's very easy to do. Interested?
« Last Edit: March 13, 2019, 03:20:49 AM by Deltarider »
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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #45 on: March 13, 2019, 07:35:38 AM »
Yes please! ...might as well.

Offline Deltarider

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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #46 on: March 13, 2019, 11:45:37 AM »
OK. Carbs in normal position (on the bike) are always numbered from left to right: 1, 2, 3 and 4. So the carb that has the chokelever, is #1. Numbering is important when we remove parts for inspection and temporarily keep them in a little jar or box that is also numbered 1, 2, 3 or 4. BTW, if it's not too much trouble, I'd appreciate if you would take pictures of each step. Pretend as if you are going to instruct us.
For the time being there are two DONT'S: do NOT remove the top lids and do NOT separate the carbs from eachother.
Now that you have the carbs on the bench with the bowls of, it's easy to carry out a few inspections. Let's start with removing the slow jets (aka idle or pilot jets), the little brass pipes next to the main jets. These cause most of the problems. The internal ⌀ is only 0,4mm and you can expect that during a long period of inactivity, when lighter fractions of the gasoline have evaporated, residu is left behind that hardens, forming an obstruction in there that will eventually reduce fuelflow. OK, use a screwdriver that fits the slot. If stuck, spray a little WD-40 or similar where the brass meets the carbbody and wait a few minutes. Usually you can unscrew them easily. Have a good look at them. They are supposed to have the number 40 stamped in. You must be able to see through the tube. If you can't see light, it needs cleaning. As a rule of thumb, do NOT use any tool that is harder than the brass the jet is made of. These jets are precisely made (see pic 1) and easily damaged which will result in your bike running too rich. I personally use stranded copper wire (see pic 2). Cheap and effective. I suppose you have a spraycan carbcleaner at hand with a straw. You could also leave the jets a night soaking in a bit of carbcleaner and clean them the next day. All orifices should be open. Now that the slowjets are removed, squirt some carbcleaner in the orifices where they sat and check fluid comes out of the tiny orifices just in front of the carbslides engineside. Realise that, when the engine idles and the slides are down, this is where quite some of the mixture exits. Fluid should also come out of the little holes you will find at the other side of the carbs, in the throats so to speak. When the bike idles, and the slides are down, this is where the air enters on its way to the little orifices you have seen in the sides of the slowjets that are there to help aerate the fuel. In the third pic below you'll see these little intakes named: Pilot system air jet. In its turn, when you squirt carbcleaner in here, fluid should come out of the holes where the slow jets sat. Whilst you're here, squirt some WD-40 in the opening named: Main Emulsion tube airjet. OK, the idle system has four orifices. We've seen three, let's move to the fourth. In the sides of the carbs are the airscrews that regulate the air taken in for the idle mixture. I'd suggest before unscrewing them, turn them in gently counting the turns (probably between 1 and 2). Do NOT exercise force, this to prevent you damage their tips. Write down the turns so you, when the cleaning is over, will be able to position them exactly where they were. Unscrew them and remove them for cleaning. You may need pointed pliers for that. Do not loose the little springs (see pic 4). Squirt some carbcleaner in the orifices where they sat. You will notice it comes down inside the carbs.
Do NOT poke anything in any of the orifices we have met. Most will be open and clean anyway provided you run the OEM airfilter element. Only the slowjet might need some gentle cleaning with the stranded copper wire. You may use compressed air to clean ofcourse.
To be continued. But so far for now. I wanna watch the BBC and the circus in the UK, but I will be back. Oh, before I go, I advise you to remove the main jets, just wiggle them out with your fingers and put them aside. Squirt some WD-40 in the orifices where they sat. This will make it easier to remove the needle jets (aka emulsion tubes) later on.
« Last Edit: March 14, 2019, 09:18:11 AM by Deltarider »
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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #47 on: March 13, 2019, 11:27:23 PM »
deltarider- i have previously done all of this (as per your instructions)... all EXCEPT messing with the air screw...

with that being said, i have done all of this again and documented each action (taken pics)  as requested (except the air screw procedure)...to be honest, i'm hesitant to do this... i REALLY dont want to mess this up...

anyhow... give me the next instructions...
at the end i will post all instructions paired with pictures (as requested)

thanks again, man.... i've learned SO much about my bike doing all of this with you and CAL and BRIAN and EVERYONE on this forum...invaluable info!!!


Offline Deltarider

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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #48 on: March 14, 2019, 04:37:34 AM »
You're just lucky it's raining cats and dogs here, giving me time to exercise my english. Every now and then I'm distracted however by another country that's fighting the effects of mass poisoning by Murdoch and the likes.
You can leave the airscrews where they are. I hope you have removed the main jets and have already squirted some WD-40 in the orifices where they sat. We can now remove the needle jets (aka emulsion tubes). You can see the pointed tips of the needles in there. It's not the needles that we are after, it's the tubes in which they slide up and down (see pic for an example). Turn the big central idle adjuster knob (well it's on the right actually, but by 'central' I mean it controls all 4 carbs) so that the gasslides rise. It is like giving more throttle. As a matter of fact you have to 'give even more throttle' by hand. This can be a bit hard, because the central return spring is a tough guy and hard to fight. We want the slides up but the real goal is to raise the tapered needles inside the needle jets. Hopefully these needle jets just drop out by gravity. If not, gently tapping the carbs - the slides (and needles) are still up - can help. If they are still stuck, bring a wooden toothpick or similar in them from below, cant it and wiggle them out. This has always worked for me. The WD-40 you have squirted in there before, may help. The needle jets normally do not need maintenance. You may run a pipe cleaner through it, but nothing abbrasive. In the sides of the needle jets there's a serie of tiny holes. They are there to help aerate the fuel. You may find some of them blocked with white stuff, the residu of water. You can use a pin to remove that residu without reaming the holes. You may squirt some carbcleaner towards the needles that will stay where they are.
Now to the main jets. Important is that their tiny O-rings are OK and will seal well. When in doubt, replace.
What else can we do? You could verify all vent tubes are open by blowing some air through them. You could check all chokeflaps move as they should, by playing the lever on the left.
Usually the O-rings around the valves (where fuel enters the carbs) are OK as they fit really tight. You could remove them, but I personally have yet to see the first one that leaks. When you do, take note of how the retaining clip under the crosshead is orientated. Whether you remove the valves or not, is your choice, but do blow air in the direction where the fuel comes from. The ^ shaped orifice in the valve (seen from the bottom), where the ^ tip of the floatneedle fits, can be cleaned with some WD-40 on a Q-tip. Do the same with the ^ tip of the floatneedle.
Assembly time. Put in the needle jets. No need to force them in. The main jets that follow, will do that for you. Just make sure the main jets go in with the tapered orifice up, this to accomodate the tapered needle tips above them. The main jets in their turn will be pressed by the leaf spring, but that comes later. After a final inspection fit the slow jets.
To ensure the floats will be moving up and down smoothly, it's not a bad idea to polish their swivel pins. Don't be tempted to 'adjust' the floattangs. We do not have ANY indication they need adjustment! You know ofcourse ;) how to position the float needles.
Check the floats can move up and down smoothly. To check float heights are correct, go to p. 60 of the Shop Manual Honda CB500 - CB550*. You don't need the float measuring tool shown there in fig. 183. Just cut your own out in an used card (see pic). Follow the instructions on p. 60 of the manual. Now, if you think, if, they need adjustment, think again. I never had to adjust them, not even one. Prescribed is 22mm. Don't worry about a mm more or less, it's acceptable and I'd rather have you keep your hands of them, to be honest. After you've put the springleafs on the main jets, you can put the floatbowls in place. You will feel some resistance which is OK. It tells you the springleaves are pressing the main jets in. I myself have replaced the 16 crossheads by allen screws (see pic). Believe it or not, ever since I can do practically all of what we have described sofar, with the carbs remaining in situ. I do not recommend to do like I do the first time, but once you know where things are, you can do it blindfolded.
The oldstyle CB500/550 Keihin carbs like to have the fuellines in the correct size. In your case it's a 30 cm long fuelline going to the T-joint that distributes fuel to carb 3 and 4 and one that is 18 cm long to the T-joint that distributes fuel to carb 1 and 2. Ideal internal ⌀ is 5,5 mm. Outside ⌀ will be around 10 mm. Abstain from inline fuel filters. They'll cause irregularities on a CB500/550.
I advise to add some fuel system cleaner to the fuel when you're ready to start riding. We here have Forté or Tunap, the Brits have Redex and I believe you have Seafoam. It's good stuff to clean and 'lube' (well not really, but kind of) parts like the swivel pins, and valve needle tips and valve orifices. Owners of K3 models IMO better have it added always, unless they ride daily.
* https://www.classiccycles.org/media//DIR_1653304/DIR_1653404/DIR_1653507/ecc6759db0a214d5ffff881effffe41e.pdf
 
« Last Edit: March 14, 2019, 08:41:04 AM by Deltarider »
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Re: ‘71 Honda cb500- first time attempt of carburetor removal/cleaning
« Reply #49 on: March 16, 2019, 11:21:18 PM »
Alright Deltarider, as per your request, I’m going to post pics/ commentary of the instructions you gave me.... hope this well, and I hope this might help others as well....

Starting with the removal of the slow jets (aka idle jet- the little brass tubes next to the main jet)...removed and cleaned