CB550 Fuel flow question

I have a 1974 CB550. It runs great for a few minutes, then it will start to run rough, like it is not running on all cylinders. I check the fuel filters and one is full, the other is dry.

I tested the flow from the fuel valve by connecting to fuel lines into a gas can. When I turn open the fuel valve, the following occurs which may or may not be normal.

When I open the valve, fuel flows from line A but nothing from line B.
If I plug line A with my finger, then fuel begins to flow from line B.
I release line A fuel is still only flowing from line B nothing from line A.
I plug line B with my finger and fuel begins to flow from line A again
Now if I release line B, fuel will flow from both lines.
If I turn the valve off, then on, fuel is only flowing from line A again.

I can repeat this process every time. I'm not sure if this is normal or not.

I have completely taken apart and cleaned the petcock, it now looks brand new inside. There are no leaks.

Part of getting the bike ready to ride this year included buying a new set of carbs that were already rebuilt. I put them on and adjusted the sync and the idle. I have not made any other adjustments to the carbs.

Is there something else to adjust that will help the fuel flow or should I try to replace the petcock?

Thanks

John

"jchardin" <UseLinkToEmail.TakeThisOut@MotorcycleForumz.com> wrote in
news:8_7454013_2a68606bcb87a03295e93fba48cfee7b@motorcycleforumz.com...
 >I have a 1974 CB550. It runs great for a few minutes, then it will
 > start to run rough, like it is not running on all cylinders. I check
 > the fuel filters and one is full, the other is dry.
 >
 > I tested the flow from the fuel valve by connecting to fuel lines into
 > a gas can. When I turn open the fuel valve, the following occurs
 > which may or may not be normal.
 >
 > When I open the valve, fuel flows from line A but nothing from line B.
 >
 > If I plug line A with my finger, then fuel begins to flow from line B.
 >
 > I release line A fuel is still only flowing from line B nothing from
 > line A.
 > I plug line B with my finger and fuel begins to flow from line A again
 > Now if I release line B, fuel will flow from both lines.
 > If I turn the valve off, then on, fuel is only flowing from line A
 > again.
 >
 > I can repeat this process every time. I’m not sure if this is normal
 > or not.
 >
 > I have completely taken apart and cleaned the petcock, it now looks
 > brand new inside. There are no leaks.
 >
 > Part of getting the bike ready to ride this year included buying a new
 > set of carbs that were already rebuilt. I put them on and adjusted
 > the sync and the idle. I have not made any other adjustments to the
 > carbs.
 >
 > Is there something else to adjust that will help the fuel flow or
 > should I try to replace the petcock?

Steady now, here seems to be a misunderstanding. There is
only 1 (one) fuel hose from the petcock (or it's the weirdest
one I ever saw). The other hose is a vacuum line to operate
the petcock.
The fuel flow that you get out of the vacuum hose means
that the membrane that opens the petcock is broken and
needs to be replaced.
Fuel should only flow with the petcock in "P" / "pri"
position or when there is vacuum (the engine is running).

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