Topic: CB500 K3 leaking fuel (video)

[Teddyhoeg1982]

Got this ‘78 CB500 K3 cheap. Had been standing still for some time and carbs were full of dirt. Took the carbs apart and Ultra sonic cleaned all parts. Did not replace anything.
Now after assembly it leaks fuel everywhere… See for yourself in the video.
I did replace the fuel lines, guess i will check if it comes from the fuel Line assembly… Any other ideas what i should look for?

[Kenzo1979]

Yeah if your float lights are not set right it will not shut off the fuel and everything will come out the overflow tubes. Another thing to check is if things were that bad inside the carbs, you may have hairline cracks in the overflow tubes themselves. Take the carb bowls off and inspect them very closely, with a magnifying glass if you have to. But you definitely need to set the float Heights right and also make sure that the little float needles are not stuck. Soak them in some PB blaster or something and squeeze the springs down back-and-forth a few times get them operational. If those float needle springs are seized, you may leak fuel.

[Kenzo1979]

Sorry just watched that video, that seems to be your float bowl gaskets, but also more likely your float height. The fuel shouldn’t even get to the level to where the gaskets are. So you’ll have to check float height and your float needle spring anyway. Looks like your overflow tubes are fine though.

[Teddyhoeg1982]

Yeah if your float lights are not set right it will not shut off the fuel and everything will come out the overflow tubes. Another thing to check is if things were that bad inside the carbs, you may have hairline cracks in the overflow tubes themselves. Take the carb bowls off and inspect them very closely, with a magnifying glass if you have to. But you definitely need to set the float Heights right and also make sure that the little float needles are not stuck. Soak them in some PB blaster or something and squeeze the springs down back-and-forth a few times get them operational. If those float needle springs are seized, you may leak fuel.

Thanks. I was curious that it seems to come out of all carbs, while before disassembly it did not leak..

By the way, getting the carb rack on and off was really hard and frustrating. Any tips to make it easier?

[Kenzo1979]

Unfortunately there’s really no “easy“ way of getting your carburetors off. It’s the number one thing everybody complains about. But my advice is to loosen the rear clamps on the engine insulator boots as much as possible without the screw coming out of the other side of the band, then do the same thing for the bands on the airbox insulator rubbers. Reach in with your fingers and push the rubbers into the airbox Plenum so they are out of the way.  Of course you have to remove your throttle cables, And if you have to, get any of your vent hoses, clutch cable, etc. out-of-the-way as much as possible. From here, the best way to get the carbs out of the intake insulators in my opinion is to try and push the entire set of carbs down so that the tops of the intake side of the carbs rocks loosen inside the insulators then wiggle it back-and-forth up and down while pulling them back until they pop out. After that you just have to slide the carbs out. 

Put them back in in the reverse, but don’t try to put them in with the airbox rubbers already installed. Retrieve them from the plenum and Save those for dead last. If they’re in good shape you can squeeze them up into place with a little finesse. 

[Kenzo1979]

Don’t over tighten your carb bowl screws.  If you strip even 1, the bowl will never seal properly and you’ll leak at some point.

[Deltarider]

Teddy, I see the original PD carbs (K3 models) have been replaced by the oldstyle carbs, but that's OK. As long as you do not apply carb setting data of the PD carbs to yours...
Leaking can occur when the O-rings have been dry for a long period of time. Sometimes it helps to give the seals time to swell again. BTW, that's why I prefer to keep my carbs wet during hibernation. The floats in these carbs never ever need (re)adjustment. Period. Only when the PO has messed with them. Some in this forum have concluded, after buying the Clymer manual, it's a maintenance thing. Well, It's not.
There's a simple and safe method to verify fuel levels are correct. It's described here:   http://forums.sohc4.net/index.php/topic,185754.msg2151647.html#msg2151647
BTW, fuel levels are not that critical as some think.

[bryanj]

MOST IMPORTANT the float adjustment level for the proper PD carbs is WAY different from the carbs you have, you need to use the settings for a 500K2

[Deltarider]

MOST IMPORTANT the float adjustment level for the proper PD carbs is WAY different from the carbs you have, you need to use the settings for a 500K2

Teddy, could it be you have applied the K3 float height data to yours that has the oldstyle carbs? Then it's no wonder they all leak. If so, you have to redo them to 22mm and consult p.60 of the Shop Manual Honda CB500-550. BTW, you don't need that gauge. You can cut one yourself from an old card (see pic). One 1mm more or less is no problem.
To all: never ever 'adjust' the floattangs. If you develop this strange desire to do not needed 'maintenance', suppress it. Hey, maybe you can mowe the lawn instead or make yourself usefull in the household.
Below is one of my floats after doing over 135.000 kms. They are all still OK. 

[seanbarney41]

Everybody freaks out about the floats...but do we know the fuel t o-rings are in good shape?

[Kenzo1979]

Everybody freaks out about the floats...but do we know the fuel t o-rings are in good shape?

True, hard to tell the source from the video.  For all we know there’s not even fuel lines connected…maybe just 2 funnels hovering over the fuel tees aimed in the general direction of their inlets with a 5 gallon plastic bucket full of fuel feeding them from two drilled holes in the bottom.  Who knows what’s going on out of view.

[bryanj]

If you did not change any O rings that could be your problem, especially on the tee pieces between carbs

[Kenzo1979]

Unfortunately there’s really no “easy“ way of getting your carburetors off. It’s the number one thing everybody complains about. But my advice is to…

Sorry, if you didn’t already know…

Forgot to mention to remove the 2 airbox bolts under the seat so your plenum will move around enough to give you a little more play and space.

[Deltarider]

If you did not change any O rings that could be your problem, especially on the tee pieces between carbs

In spite of harsh treatment by me and after passing all kinds of hydrocarbons, my O-rings on the tees between the carbs still refuse to leak. Replacing them, implies separating the carbs from the rack. Honda has forseen that and therefore put not one but two O-rings on each side for robustness. If you keep your carbs in winter in a natural state - which is wet - they'll live forever. If you drain the carbs to store dry for a long period of time, you can expect leakage afterwards. Often the problem will cure itself, once the seals haven swollen again.

[Teddyhoeg1982]

Teddy, I see the original PD carbs (K3 models) have been replaced by the oldstyle carbs, but that's OK. As long as you do not apply carb setting data of the PD carbs to yours...
Leaking can occur when the O-rings have been dry for a long period of time. Sometimes it helps to give the seals time to swell again. BTW, that's why I prefer to keep my carbs wet during hibernation. The floats in these carbs never ever need (re)adjustment. Period. Only when the PO has messed with them. Some in this forum have concluded, after buying the Clymer manual, it's a maintenance thing. Well, It's not.
There's a simple and safe method to verify fuel levels are correct. It's described here:   http://forums.sohc4.net/index.php/topic,185754.msg2151647.html#msg2151647
BTW, fuel levels are not that critical as some think.

My carbs are stamped 649A which I think is not PD version?

[bryanj]

As said before they are off a CB500K0,1or2

[Deltarider]

These 649A carbs were for the CB500(K0), CB500K1 and the CB500K2 (ED, G also known as GENERAL EXPORT). Your K3 can use them well, as the engines do not differ. Other markets like US, UK and France had the 627B carbs. We still don't know if the difference between the 649A and 627B carbs is only in the jetting. Possibly they had different venturis. We don't know. I've made an overview of these oldstyle CB500/550 carbs.

[Teddyhoeg1982]

So I took the carbs off again. This time I pushed the airbox rubbers out of their sockets and removed them before pulling the carbs, which made the removal much easier.

When I want to check the float height, the floats Seem so heavy that they just push the needle spring down. The floats touch the needle spring at 22 mm height, but just Fall down to 18 mm when i let go of my grip.

Could this somehow be bacause i Ultra sonic cleaned the floats at 50 degrees celcius, 122 degrees fahrenheit? It does not Seem they took in water, but i am suspecting if they just Fall to the bottom of the housing and does not rise to the top and close the needle? See the video.

https://youtube.com/shorts/IhuL-NQEm-s?feature=share

[bryanj]

You dont seem to have grasped the idea of float level setting, try reading the manual for the earlier 500

[Teddyhoeg1982]

You dont seem to have grasped the idea of float level setting, try reading the manual for the earlier 500

See the two pictures below. Float height should be 22 mm with this method. Mine are 18 mm., but it seems to be because the floats just compress the spring in the needle and Fall to 18 mm. The floats would touch the needle spring at 22 mm in my case.

[Deltarider]

Teddy, please go to p.60 of the genuine Shop Manual CB500-550. There it is shown, you have to do it sideways, to avoid gravity play a role. The idea is the float needle is not compressed. https://www.dropbox.com/s/88zdzlj8olqi8pl/Honda%20CB500_CB550%20%20Four%20Service%20Manual.pdf?dl=0
You don't need that special gauge. Cut your own from an old card.

[Teddyhoeg1982]

Teddy, please go to p.60 of the genuine Shop Manual CB500-550. There it is shown, you have to do it sideways, to avoid gravity play a role. The idea is the float needle is not compressed. https://www.dropbox.com/s/88zdzlj8olqi8pl/Honda%20CB500_CB550%20%20Four%20Service%20Manual.pdf?dl=0
You don't need that special gauge. Cut your own from an old card.

Thanks a lot! Then I can confirm that the float height is 22 mm and correct. So that is not where my problem is then.

[Teddyhoeg1982]

Just noticed that the fuel Lines are too thick and not able to go all the way over the fuel inlet tubes. See below. Maybe the leak is coming from here. Will try to purchase some slimmer fuel Line.

[Deltarider]

The correct dimensions are: for the CB500 and CB550Ks: 18 and 30 cm length for the models with the bowltype petcock and 17 and 28 cm for models that have the newer style petcock*. Do not be tempted to have them even one cm longer. For the tube that supplies carbs 3+4, use the soft metal clamp in the middle front side as shown in the pic (btw, horizontal is good enough) for proper routing. Ideal inside ⌀ of the fuel lines is 5,5 mm. Outside ⌀ will be around 9-10mm. Have this and the lines will not kink. Abstain from extra inline filters. Some have been lucky with them, but my experience is that they can't be trusted. Often it isn't that filter itself, but the rerouting of the fuel line that - sometimes intermittent - impedes a proper delivery of the gas.
*Your K3 model may have a different tank and petcock, so length may also vary some.

[Teddyhoeg1982]

Just another Update. The o rings on the main jet and needle tube seem really dried out and for the needle housing is probably letting fuel seep past them. See video.

https://youtube.com/shorts/e_mKya8iF-8?feature=share