Topic: CB550 Petcock Leak

[10ianbrown]

Hi all, I'm a brand new contributor to the forum after lurking for quite some time as I've been tinkering with my '76 CB550. I've spent quite a bit of time and a little bit of money over the past few months in my garage attempting to stop the petcock from leaking fuel.

When the petcock is in the "stop" position gas slowly dribbles out of the forward-most nipple. It does this whether it's attached to the fuel lines or not, and regardless of whether the fuel cap is open or not. In the other positions it seems to work as it should, flowing from one or both of the nipples freely.

I've replaced the whole petcock twice, once with a cheap-o petcock on amazon, and then again with the nicer version I found on Common Motor. Neither have solved this is any way. I then found on this post (http://forums.sohc4.net/index.php?topic=51569.0) that the petcock's washers might be the issue so I ordered bolts with the red washers from old bike barn website and no luck there either.

Any ideas as to what's causing the leak?
Also, the reason I know it continues to run when it's hooked up to the fuel lines is because fuel leaks out of carb 1's overflow tube- I know this is its own separate issue and that the float height needs to be fixed.

[newday777]

Welcome aboard the forum 10ianbrown from another brown.
You said you have a 1976 CB550, and that you got the screws and red washers to install it.
1975 and 1976 shouldn't need those screws and red washers as they use one the threads on with a big nut to a bung on the tank(on the left side of the tank.
Post a picture of your tank and petcock.)

Here is the petcock the 76 uses.

https://www.southsoundhonda.com/--xpartsstream#/Honda_Powersports/CB550KA_(76)_550_FOUR%2c_JPN%2c_VIN%23_CB550K-1230001/FUEL_TANK_%2b_AIR_CLEANER/f77665b3-598c-4e35-ad4b-7a873770e3e5/e4d1e2bc-0ddd-4900-af3f-466f033bd48a/y

[10ianbrown]

Thanks for that, newday. Funny enough I actually bought that petcock for my first attempt and realized quickly it wasn't the right model. The bike's previous owner mentioned swapping the tank at some point, and I saw on Common Motor that some '76 tanks actually do use the model I'm describing. Check out the description on this item: https://www.common-motor.com/honda-cb550k-early-petcock

[Stev-o]

I currently have a petcock issue on one of my bikes, I believe it is the ethanol fuel causing the issue.

In the past, I have not had good luck rebuilding petcocks or buying cheapass ones, buy the Honda petcock and be done with it.  Looks like the Common Motors petcock is an aftermarket one as well.

As far as the carb leak, try running the motor dry w/o a fuel supply and tap on the bowl to force the float to move down, sometimes they get stuck and need a nudge.

[craz1]

I had that same issue with an aftermarket petcock for my RD 350. Just would not seal in the off position. Tried one more and that one has been fine. What I did was remove the bowl in the off position and put a catch bowl under it so I could see where the gas was coming from. I also thought it could be the screws but it was just a bad casting. I agree buy OEM if you can.

[10ianbrown]

Thanks everyone! Just to be clear, will fixing the float issue resolve the gas actually leaking since it won't flow freely when the floats are up?

[craz1]

No the floats are not a positive shutoff. If the petcock is leaking there is a great chance of fuel leaking past the float needle and overflowing the carbs or worse, like flooding the intake and into the pistons, then into the crankcase in sever situations. Got to have a positive off at the tank.

[RAFster122s]

Problem is Honda no longer offers that OEM petcock and CMSNL doesn't have any either... So, you may need to pick up a fuel shutoff valve. I know DrATV offers a tiny plastic one that is black and red but I believe it is made for 1/4" fuel line.
Lawn mower repair shops sometimes have these kinds of shutoffs too, but usually made for SAE lines instead of metric lines.

[Kenzo1979]

Common motor is a pretty decent place. If I had a problemlike this, I would reach out and talk to people and see what they can do for me. Tell them about the one you bought from them and ask for a replacement. See if they can actually test one out and send you one that works properly. You may be surprised, they may be cool and agree to work with you and do that for you. If you can find an OEM on eBay, etc., use the gaskets and other parts from the aftermarket ones you bought and try to make your own working version.  Good luck!

[craz1]

I agree to work with them on the petcock issue. Some of these aftermarket parts can be a pain, but at least someone has taken the time to support the old bikes especially if you cant get OEM anymore.. A lot of times they need the feedback to improve and they may have had a bad run of them. If you cant get it figured out look into PINGLE petcocks. If you have the type that mounts with two screws then you would need an adapter plate to use on of the PINGLE valves.

[newday777]

Thanks for that, newday. Funny enough I actually bought that petcock for my first attempt and realized quickly it wasn't the right model. The bike's previous owner mentioned swapping the tank at some point, and I saw on Common Motor that some '76 tanks actually do use the model I'm describing. Check out the description on this item: https://www.common-motor.com/honda-cb550k-early-petcock

I'm wondering if your bike has a earlier tank on it. How about posting a picture of your tank and bike vin plate(maybe you actually have an earlier bike??)

[Stev-o]

I agree to work with them on the petcock issue.

+1.  I had same issue with my Z1, bought an aftermarket petcock and it leaked [OEM not available].
Z1parts.net sent out another and it has been good since [5+ years]

[10ianbrown]

Thanks for the input everyone. I think I've figured out that my tank is from a '72 CB500 (keep forgetting to grab a good pic to post here) and I've gotten a cut-off valve installed in the fuel line. Working on the float height this week, and have emailed common motor about the leaking petcock. Hoping to have it up and running this week!

[exponent]

To hijack the thread a little. I have a 78 tank with the single line petcock. It was leaking and I wanted to know if the motion pro 3/16 fuel valve is an ok choice? Does it restrict flow too much? Have a repro petcock on the way but I'm assuming low quality

[Stev-o]

I wanted to know if the motion pro 3/16 fuel valve is an ok choice? Does it restrict flow too much?

I would not think so, I use 3/16" fuel line on my bikes.

[rollypoli]

Thanks for that, newday. Funny enough I actually bought that petcock for my first attempt and realized quickly it wasn't the right model. The bike's previous owner mentioned swapping the tank at some point, and I saw on Common Motor that some '76 tanks actually do use the model I'm describing. Check out the description on this item: https://www.common-motor.com/honda-cb550k-early-petcock

Do you still have the nut style one?? mine is leaking a ton and is out of stock everywhere

[newday777]

Thanks for that, newday. Funny enough I actually bought that petcock for my first attempt and realized quickly it wasn't the right model. The bike's previous owner mentioned swapping the tank at some point, and I saw on Common Motor that some '76 tanks actually do use the model I'm describing. Check out the description on this item: https://www.common-motor.com/honda-cb550k-early-petcock

Do you still have the nut style one?? mine is leaking a ton and is out of stock everywhere

A lack of people posting a picture of what they have makes it hard to know exactly what they have and need.

[Little_Phil]

I currently have a petcock issue on one of my bikes, I believe it is the ethanol fuel causing the issue.

I've found the aftermarket petcocks are hopeless with E10. The genuine Honda petcocks have been fine. I have three of this type on various thanks.

[rollypoli]

Thanks for that, newday. Funny enough I actually bought that petcock for my first attempt and realized quickly it wasn't the right model. The bike's previous owner mentioned swapping the tank at some point, and I saw on Common Motor that some '76 tanks actually do use the model I'm describing. Check out the description on this item: https://www.common-motor.com/honda-cb550k-early-petcock

Do you still have the nut style one?? mine is leaking a ton and is out of stock everywhere

A lack of people posting a picture of what they have makes it hard to know exactly what they have and need.

True, I have the more rare one(it seems) for my 75 cb550, that you posted a picture of, it seems to have been out of stock for a while, and they don't sell rebuild kits for them, mine leaks out of the face and I lost the oring when I had it apart so I gave up on trying to repair it, though now I'm in a pickle