Topic: petcock problems

[Emodog04]

The petcock on my 76 cb550 will not turn off completely.  It leaks gas into the carbs and is hard to start cause it's always flooded.  Also it is fouling plugs like crazy.  I bought a new old stock petcock that was similar except it had only one fuel out were mine has two. I put the insides out of the new petcock in my old petcock body, but still have the same problem.  Any suggestions to what I might do?  could i put a seperate cut off in the line someway?

thanks,

[TwoTired]

Sounds like you have two problems.  The float valves aren't sealing, AND your petcock leaks.
Have you checked for fuel contamination?

The valve has a plastic cone inside that if scored will cause leakage.  The scoring can also occur in the mating metal body of the valve.  The damaged ones I've seen were scored from rust scale entering from the tank.  These particles get "cleaved" during valve operation and then embed themselves into the soft plastic valve cone.  Each time the valve is operated thereafter the valve body and/or the valve cone scoring worsens.  The in-tank filter screen is supposed to protect the valve from this damage.

I've not been entirely successfull at restoring these valves once they are scored.  And, I've found that exchanging parts with another good valve generally just spreads the disease. And, you end up with two leaking valves.

If you reassemble the one outlet petcock with it's orignal parts (assuming they aren't already damged from the parts swapping), then you can simply put a "T" fitting inline so that both carb feeds can attach to the one petcock outlet.  Reserve will still work.  Later Cb550s had this routing from the factory.

Cheers,

[Dennis]

Have you removed the petcock to check the screen and the interior of the tank? Or did you just exchange the parts?
BTW: I just purchased parts for a similar petcock (for a CB750F) from the local Honda dealer so I would guess that whatever you need might still be available from Honda.
You don't say where you got a NOS petcock, but I'd bet it wasn't inexpensive where ever you found it.
As far as your engine problems are concerned, I am in total agreement with twotired

[Emodog04]

I think the valve seats are sealing because I can take the bowls off and lift up on the floats and the gas flow stops.  I may try putting the nos petcock back together and useing the t valve.  What type of T valve do I need to get, and where could I find it?  Would it also help to eliminate the filter in the tank and put a inline filter on?

[Dennis]

I think the valve seats are sealing because I can take the bowls off and lift up on the floats and the gas flow stops.

This is not consistent with your earlier statement that the carbs are flooding. The only way those carbs can flood is if the float needles are leaking. It could be intermittent. Sediment traveling down from the tank can hang the valve open and then wash away when you start the engine.

Would it also help to eliminate the filter in the tank and put a inline filter on?

An inline filter won't hurt but you never told us the condition of the screen in the tank. Why would you want to remove it? What purpose would that serve. TwoTired just told you that it is there to protect the petcock. Did you use the one that came with your NOS petcock? Or is the old one good?

FYI: On some of my bikes (CB750F and Yammie RZ350 YPVS) I use the OEM filter in the tank with an additional in-line filter. Works fine.

[Emodog04]

I have just rebuilt the carbs so I don't think the valve seats are struck open, but I guess it's possible.  It hasn't had many miles put on it since I rebuilt them.  But I am getting gas leaking from the overflows and I assumed it was because the petcock doesn't close off.  When I try to start it the bike it acts like it is flooded and the number one plug fouls.  This is a recent problem that wasn't happening last time I rode the bike it had sat for about 2 weeks.  But like I said I can lift up on the float and the gas flow will stop.  Perhaps the float is set to high?  But either way I want to stop my petcock from leaking.  The nos petcock didn't come with a new filter, and the guy I bought it from said it would be better to use an inline filter anyway.

[Dennis]

I have just rebuilt the carbs so I don't think the valve seats are struck open, but I guess it's possible. .......I am getting gas leaking from the overflows and I assumed it was because the petcock doesn't close off. When I try to start it the bike it acts like it is flooded .....

The nos petcock didn't come with a new filter, and the guy I bought it from said it would be better to use an inline filter anyway.

So what is the condition of the existing filter?
Are you getting any sediment in the carb bowls from the tank?
What is the condition of the interior of the tank?

Also, there are other reasons for the overflow. As you said, float levels. Damaged overflow tubes is another. Are the spring loaded plungers on the needles working? Or are they varnished and stuck?

If the screen in the tank is not in good condition, I woud contact Honda to see if it is available. When I got the one for the 750 it came as part of a kit which included several other components. It may even be the same part number, who knows?

[Emodog04]

The screen in the tank is actually in pretty good shape i cleaned it before putting the carbs back on.  The tank has also been cleaned and coated with a rust protectent.  But I guess it would almost have to be trash holding the valve seat open.  That would explain the flooding and the fouling of the plug in number 1.  but I still don't under stand what is keeping the petcock from closing off.  The body is in good shape but its just not closing completely.

[Dennis]

I still don't under stand what is keeping the petcock from closing off. The body is in good shape but its just not closing completely.   

Got to be something going on there. Some damage that you may not have seen is what comes to mind. Or a piece of debris stuck to the valve core. I'm trying to remember the design of that valve, I think that damaged (rubber) seals would allow fuel to leak outside the valve body.

But I guess it would almost have to be trash holding the valve seat open. That would explain the flooding and the fouling of the plug in number 1.

 

Maybe, you still haven't said if you are finding sediment in the carb bowls. If you are maybe an in-line filter might help. Many wii stop particles smaller than the screen in the tank can stop.
Have you checked the (float) needle for wear, damage or a stuck plunger?

A couple of months back, I was helping a friend get an old "400 twin" running. Among other problems the carbs were overflowing as would be expected. The plungers on the needle valves were stuck and the local Honda stealer was only too happy to provide special order replacements for a large amount of money. We installed the new needles checked them before screwing on the float bowls and put the carbs back on the bike. Fired it up and what do you know, peeing gasoline all over the floor. Upon close examination a piece of varnish was found stuck to the tip of the brand new float needle. You must study these things carefully. Removed the flake of varnish (which was soft enough to disappear when rubbed between my fingers) and overflow was gone.

Good luck

[bryanj]

If you have taken the petcock off several times check the condition of the sealing washers under the retaining screw heads as if theses aint good gas will continuously bypass the off position on the tap