Topic: 1971 cb750 petcock

[bradengineer]

if the brass tube that's attached to the petcock inside the tank has a crack down it, would that allow too much gas into the carbs? When i let my bike sit it leaks gas out the overflows of the carbs if the petcock isn't shut off. I have checked the float heights and they seem right. I'm def not a mechanic but have started running out of ideas from the forums and would like to fix this myself.

[Duke McDukiedook]

These bikes pee a little if you don't turn the petcock off when you put the bike away for more than a few hours.
Part of owning the machine.

You can solder the brass tube or shrink tube it, soldering it is probably the best option.
The tank level will just go lower before you need to switch over to reserve, but you also don't have that much in reserve when this happens.

[Gordon]

No, a crack in the petcock stand pipe will not cause too much gas to flow to the carbs.  The amount of fuel going into the carb bowls is regulated by the needle valves.  

Either the fuel level is set too high or one or more of the valves aren't closing completely, or one or more of the overflow pipes in the carb bowls are cracked.  This is usually caused either by some kind of grit in the valve seat, or a sticking float, but it could also be something else like a float that's taking on gas.  

[Gaither]

No, a crack in the petcock stand pipe will not cause too much gas to flow to the carbs.  The amount of fuel going into the carb bowls is regulated by the needle valves.  

Either the fuel level is set too high or one or more of the valves aren't closing completely, or one or more of the overflow pipes in the carb bowls are cracked.  This is usually caused either by some kind of grit in the valve seat, or a sticking float, but it could also be something else like a float that's taking on gas.  

As you know, the shrink tubing trick will also work on the overflow tubes in the carb bowls.

My '77 550F was leaking badly at idle [carbs were very dirty]. When I had 'em cleaned we found 2 overflow tubes were cracked almost full length. With that condition they leak freely. Nothing short of replacement or the shrink tubing trick will stop this kind of leak [other than closing the petcock].

Keep the rubber side down.