Topic: K1 bizarro petcock stuff

[phil71]

I understand how this guy works, and did rebuild on it a few months back. Cleared the crap out, chased as much as i could with gtr strings etc..
Bike started running funny, and mostly on 2 cylinders, the two that run off the rear tap. So i took some clear hose and fed them into a gas can. Turned on the tap and one flowed great, the other just barely trickled.
Then, I plugged the free-flowing one, and the other came to life, but not AS lively as the rear tap.
  Took it apart and fed compressed air thru everything. Far as I can tell, the 2 brass outlets are just "Y"'d , and the blown air confirms this, and seems free as can be.
Why the hell would one flow less than another?

[seanbarney41]

Fuel line routing?

[ekpent]

That has been noted before that one spigot on the petcocks seem to flow first or more than another so yours is not an anomaly.As Sean mentioned pay close attention to the fuel line routing.

[phil71]

I thought of that, which is why I used some clear line for testing. Both were straight down and into a gas can.

[slowjo]

I have the same problem on my CB750. And like you said it doesent sound right! My lines are routed right also. But even without any lines hooked up and the petcock is turned on gas flows out  better on one side, and drips out the other.

[HondaMan]

The "alternate flow action" you see has always been a trait of the dual outlet petcocks, even on the old Twins. It doesn't hurt anything in operation.

But, what DOES cause trouble is the fuel line routing on the bike itself. With dual outlets. the hoses must NEVER run vertically, so check for that. On the 750, the hoses should come out of the petcock, immediately turn sideways and pass through a hole in the carb mount bracket, then route toward the center of the bike, turning downward to their respective Tees. Too often, I have seen the hoses hangin DOWN, then going back up to the Tees: this always causes trouble in the form of low bowls.

Another thing that can cause uneven flow: if the O-rings on those Tees are real old and are weeping a tiny bit of gas: this indicates they are also leaking the very small hydrostatic head pressure of this gravity-drain system. This can make one side stop flowing until enough fuel happens to wet the area enough to create a seal, then it flows that side again by balancing the suction between the two pipes. New O-rings will fix it up. 

[slowjo]

So if the fuel lines are a little long they could be a problem? Because the lines will be more vertical from the "T" ?

[phil71]

O rings in the Tee?
 You don't mean where they meet the carbs?
If you mean at the petcock, nothing's leaking. The lines have always been routed in exactly the OEm way.

[HondaMan]

So if the fuel lines are a little long they could be a problem? Because the lines will be more vertical from the "T" ?

Yes, that can cause a bubble to trap in the upward bend. It should be flowing downward the whole trip to the Tee, or at least horizontal, like when it runs along the tops of the head's hoses enroute to the far Tee.

[HondaMan]

O rings in the Tee?
 You don't mean where they meet the carbs?
If you mean at the petcock, nothing's leaking. The lines have always been routed in exactly the OEm way.

That Tee between the carbs: each Tee has 4 O-rings on it. The "extra" one on each half of the Tee was added to ensure the system never leaked the tiny bit of vacuum that makes it work.