Topic: CB550 Four K3 1979

[Cruiser]

I don't think these floats can leak! If you cut one, you'll see they're all foam. BTW, this is explained in the video I've posted in reply #116, from 10:05 - 10:20. No cavity in yours.
Do your choke flaps function as should?

I'll redo the test when I have the new ones. But they remained wet on that part where you see the tiny crack. So even if it has foam, I'd think the foam absorbs the fuel and in turn gets too heavy. Thats maybe why in my video you see the level stabilize (the float floats and closes the valve) starts to fill up (float drops since its heavier) and the fuel level goes all the way up.

The choke works as it should I think, closes the flaps when pulled. They spring back to the off position quite easily.



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[Deltarider]

A test to find out, is to swap the float - and only the float - with one in another carb and see if the problem follows.

[Cruiser]

A test to find out, is to swap the float - and only the float - with one in one in another carb and see if the problem follows.

I'll do that test tomorow.

Assuming it's not the float that sinks, what other options are there? Where would you go and look?

The float itself isnt getting stuck, moves up and down freely. Any other way this can overflow then? When I manually push the float up it also closes as should (and I gently push it up just when the valve seats, not pushing the spring in)

I have no clue.

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[Cruiser]

When maintenance is needed, cleaning the floats swivel pins is recommended*. A little naphtha or WD-40 will do. You may use one of your granddad's pipe cleaners. Do not use anything abrasive. Swivel pins are best removed by using your fingernails. If you must use pliers, I repeat must, do not pinch the pin's ends!
Is the O-ring around the float valve seat OK?
* Here's why. Although this video deals with the oldstyle carbs, the principle also applies to your PD carbs. From 17:00 - 18:20 it shows what goes on in practice.

Note how gentle the movement is and how little force is exercised. Note also the little pin at the bottom of the needle does not compress. It's only there to absorb eventual shocks. So measurements should be made with the float's tang touching that little shock absorber, but not compressing it!
Video courtesy Gruzzel

Concerning the o-ring around the float valve seat... I remember not replacing these since I couldnt get the valve seats out. So that could also be a culprit. They are pressed all the way in, not sure how to get them out without damaging the brass?

Is there an O-ring even in the seat? Since I've seen other just pressed in.

Any tips?

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[Deltarider]

Is there an O-ring even in the seat? Since I've seen other just pressed in.
Any tips?

I'm afraid not. It's been too long I had a look at these but I suppose they're more or less similar to those on mine. I can wiggle them out. If you have the needle removed, you could check by putting a thumb over the opening and pour gas into the tube that feeds it and see it it leaks.

[Cruiser]

Is there an O-ring even in the seat? Since I've seen other just pressed in.
Any tips?

I'm afraid not. It's been too long I had a look at these but I suppose they're more or less similar to those on mine. I can wiggle them out. If you have the needle removed, you could check by putting a thumb over the opening and pour gas into the tube that feeds it and see it it leaks.

I think there isnt either.

Anyway, did the float swap and test. Hands down you are right, it works in the other carb. But now again I have strange findings...

Using the clear tubes on the underside of the carb bowl, so with the drain open, 1, 2 and 4 stabilize at the float height level. 3 does as well for a fraction and then starts to flood through the idle air hole.

However, if I close the drain screw and fill the carbs by opening the petcock, none of them are overflowing (test on the bench).

So I'm totally lost right now. When they where on the bike, I occasionally saw an overflow issue while testing this 2 days ago. Thats why I did the clear tube test.

Why does number 3 overflow with the clear tube test (and thus when the drains are open) and the others don't? I'm pretty sure I have a leak since last time I stopped at a red light, I smelled gasoline fumes. So I think it was overflowing then and spilling out the air filter drain.

Or am I testing this the wrong way?!

Getting my grips on carbs... They are complicated, but I'm happy to have learned this much already.

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[Deltarider]

Do all carbs vent?

[Cruiser]

Do all carbs vent?

What do you mean? Where should they vent?

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[Deltarider]

OK, study the parts list for your model first. It is here: https://www.honda4fun.com/dwnload/Part-List/CB500/CB500-K3-CB550-K3-K4-Parts-List.pdf You can identify your model by comparing the frame- and enginenumber of yours to those listed in the first few pages of the parts list. The carb nummers are also there. The carbs themselves are in p.33 - 40.
I've seen them with a vent tube, but I have also seen later models that have a little vent hole in the carb body (see pic below). They should be open. Carbs need to have vents, so the float chambers can all have the same (atmospheric) air pressure to guarantee bowls will fill equally. In the last pic you see two pipes next to eachother, one is for fuel supply, the smaller one for venting. Carb vents are interconnected by small rubber tubes in between them. It's easy to check all carbs vent.

[Cruiser]

OK, study the parts list for your model first. It is here: https://www.honda4fun.com/dwnload/Part-List/CB500/CB500-K3-CB550-K3-K4-Parts-List.pdf You can identify your model by comparing the frame- and enginenumber of yours to those listed in the first few pages of the parts list. The carb nummers are also there. Carbs are in p.33-40.
I've seen them with a vent tube, but I have also seen later models that have a little vent hole in the carb body (see pic below). They should be open. Carbs need to have vents, so the float chambers can all have the same (atmospheric) air pressure to guarantee bowls will fill equally.

Aah ok, I thought you meant I needed to make a seperate vent during the clear tube test. Miscommunication.

I'll check the vent tubes again.

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[Deltarider]

I've edited my last reply.

[Cruiser]

I've edited my last reply.

Deltarider, you are truly a life saver!

So when I cleaned these carbs (almost a year ago) I checked the vents and all other holes to make sure they where free with a guitar string before ultra sonic cleaning.

Now a year later, when I finally installed, them I never thought of the vents anymore and sure enough, carb 3 had a clogged vent!!

Sticked the trusty guitar string through again and tested... No more overflow!

I cancelled my order on new floats since they worked when swapped into another carb.

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[Deltarider]

If your model has a tube for venting, make sure it is (and remains) free and will not be pinched closed by anything like the main stand. Some owners had to cut an inch of that tube's end. It's curious: all problems with CB500/550 carbs not venting which I have seen, were K3s.

[Cruiser]

If your model has a tube for venting, make sure it is (and remains) free and will not be pinched closed by anything like the main stand. Some owners had to cut an inch of that tube's end. It's curious: all problems with CB500/550 carbs not venting which I have seen, were K3s.

As far as I know there are no tubes from the vents out (not even linking the carbs).

If you where to connect them, only 1 and 2 are opposite to each other and 3 and 4. You can't seem to link 2 and 3. Since the vent for 2 is on the left and the vent for 3 is on the right.

There are also no link tubes on the diagrams for that carb.

Other type carbs seem to be linked or interconnected.

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[Deltarider]

[...]
If you where to connect them, only 1 and 2 are opposite to each other and 3 and 4. You can't seem to link 2 and 3. Since the vent for 2 is on the left and the vent for 3 is on the right.

That's what owners of models with the oldstyle carbs have. 1+2 are connected and 3+4. From the right side of 2 and the left side of 3 two 3,5mm vent tubes go to somewhere in the vicinity of the battery.

There are also no link tubes on the diagrams for that carb.
Other type carbs seem to be linked or interconnected.

Yes, there are different models. So your model carbs have the small vent openings in the bodies as seen in the pic below?

[Cruiser]

See picture with colored circles
Red looks like dummy ports, those holes dont appear to be bored out (see the other picture as well). I assume these probably were on other carbs but they didnt change the design mould for these and just didnt bore them?

The yellow circles are the vent tubes but according to the schematics are not connected.

Also inside the bowl, red is the place where the dummy port connects, there is no hole. Yellow is where the vent tube connects to and has a hole.



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[Cruiser]

She's giving me more head scratches

I had 2 very good rides after the carb adjustments, however on the last ride I blew the main fuse. No problem, I had a spare, changed it and I was able to get home with no further issues. I knew there was a loose cable from the buzzer in the headlight, figured that might created a short.

2 days later I wanted to go for another ride, since she drove beautifuly the ride before I wasn't expecting issues, however she was down on power, lagging when I opened the throttle. So after 2 kilometer I returned home and started checking for issues.

Cylinder 2 was cold. Spark? Yes! Fuel? Yes (spark plug is wet).
I've let the cylinder dry out a bit and tried several hours later with 4 new plugs. 2 still doesn't ignite. However I have spark and fuel (again spark plug was wet). I also blew compressed our into the main jet just to be sure nothing was clogged up.

Timing is good (wasnt changed either after the last ride).

Compression (measured cold with throttle open, still new rings on the pistons as well, only has run 500km)
1: 140
2: 120
3: 125
4: 140

Never had issues before on cyl 2.

Coils are good (new) and I have spark on cyl 2. Same issue when I change lead cables from cyl 2 and 3... Cyl 2 remains cold.

Ideas are appreciated.

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[Deltarider]

Check for arching between plugcap and the head. Best seen in the dark. Also check its resistance and the connection.

[Cruiser]

Check for arching between plugcap and the head. Best seen in the dark. Also check its resistance and the connection.

I renewed all plug caps last week (before the last good ride) so I'll give that a check when its dark.

However shouldn't it then fire when I switch cyl 2 and 3 cables around?

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[RAFster122s]

Did you trim back about 1/4 of the insulation of the wire for the new caps?
Might have an issue with the plug on the dead cylinder. Apparently lots of counterfeit plugs in the supply chain and sometimes even the real ones won't fire under compression.
Pop a new plug or swap the plugs from a good cylinder to see if that is the issue.

[Deltarider]

I renewed all plug caps last week (before the last good ride) so I'll give that a check when its dark.
However shouldn't it then fire when I switch cyl 2 and 3 cables around?

In principle Yes. Arcing (by plugcaps and/or HT wires) is a known issue CB500/550s have. When you unscrew caps, check their resistance. Another thing: I hope you don't have R(esistor) sparkplugs. And - as Rafster suggested - make sure connection is good.

[Cruiser]

Did you trim back about 1/4 of the insulation of the wire for the new caps?
Might have an issue with the plug on the dead cylinder. Apparently lots of counterfeit plugs in the supply chain and sometimes even the real ones won't fire under compression.
Pop a new plug or swap the plugs from a good cylinder to see if that is the issue.

I had to cut them to length, but I didn't trim them (you mean trimming them as in, removing a small part of the insulator to expose a little part of the copper wire?). I just cutted them with nippers and then screwed the cap on as far as I could again.
The plug itself can't be the issue I think. When I take it out of the cylinder, and place it on the engine, I can clearly see the spark between the electrodes.

I'll see if I can spot any arching but I need to do it in the evening then so its dark.

I renewed all plug caps last week (before the last good ride) so I'll give that a check when its dark.
However shouldn't it then fire when I switch cyl 2 and 3 cables around?

In principle Yes. Arcing (by plugcaps and/or HT wires) is a known issue CB500/550s have. When you unscrew caps, check their resistance. Another thing: I hope you don't have R(esistor) sparkplugs. And - as Rafster suggested - make sure connection is good.

The plugs have 5 ohm resistors (NGK XD05F and VD05F) and I use the Denso X22ES-U, so without any resistor.

[Deltarider]

When idling and in absence of other surrounding sounds, you might hear it crack when it arcs: a sharp very short sort of 'crickr'. Also check the routing of the HT wire and see to it, the wire does not contact the head or make ground elsewhere.
Testing a sparkplug 'outside' so to speak, is no guarantee, I'm afraid. Just use another sparkplug to be sure.
When the HT wire has been screwed on and of a couple of times, you may need to shorten it by say 2 mm, so the screw inside the top of the plugcap has a good grip in the core, resulting in a firm connection.

[Cruiser]

So I looked for any arching and couldn't see any obvious sparks anywhere.

Took a small end of the lead wire, reattached the new cap, still nothing. Measured the new cap, resistor reads 4.75k ohm. So resistor appears to be good.

I measured the old cap, resistor reads 4.3k ohm. Placed that on the wire and cyl 2 fires.

It gets hot, but not as hot as the others though (still hot enough to burn my.fingers though ).

No idea why the new plug cap fails, and since it doesnt get as hot as the others, I'm wondering if she still arches or leaks sparks anywhere.
 


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[Deltarider]

[...] Measured the new cap, resistor reads 4.75k ohm. So resistor appears to be good.
I measured the old cap, resistor reads 4.3k ohm. Placed that on the wire and cyl 2 fires.

As far as resistance, both caps are good. Strange one doesn't work, because there's clearly continuity.

It gets hot, but not as hot as the others though (still hot enough to burn my.fingers though ).

That's good enough. I'd take her for a ride.

[...] I'm wondering if she still arches or leaks sparks anywhere.

I doubt it, arcing always goes with a very abrupt and ultra short but noticeable hesitation in rpm.