Petcock testing after storage

[MisterCinders]

I have an OEM petcock that I pulled from the bike when I had some fuel overflow issues last year. The overflow cause turned out to be sticking slides/floats, so I am all but certain that the petcock worked fine.

Nevertheless, I have been using an aftermarket petcock from Z1, and it works great. Because I keep multiple tanks/seats around (so my bike can match my outfit, natch), I'd like to return this petcock to service.

I want to test the petcock beforehand to make sure it hasn't gotten out of whack in storage. I'd hate to put the thing on and find it now leaks because of dried out seals or something that requires me to wrestle with a full tank, etc.

So are there any methods for testing a petcock's function before installing it? Alternatively, what might I do to test it installed on a spare tank, without actually running it on the bike/engine?

[tkent02]

Whether it flows and stops with vacuum, easy to check. Use a syringe or something to suck on the vacuum hose, watch the fuel flow and stop.

Testing whether or not fuel will seep through when it is closed is harder. Put some gasoline in the tank, set it up several feet above the floor. Run a hose from the outlet to a jar or something you can cover up. Use prime to fill the jar about half full, and cover it so the gasoline won't evaporate. Make sure the end of the hose is under the liquid in the jar.

Mark the level in the jar and come back later. If the jar has more fuel in it that it did before it is seeping, and can allow carbs to keep overflowing until the tank is empty if they have a weak needle valve.

With a tight petcock the level of the fuel should not rise at all.

[hikermikem]

Whether it flows and stops with vacuum, easy to check. Use a syringe or something to suck on the vacuum hose, watch the fuel flow and stop.

Testing whether or not fuel will seep through when it is closed is harder. Put some gasoline in the tank, set it up several feet above the floor. Run a hose from the outlet to a jar or something you can cover up. Use prime to fill the jar about half full, and cover it so the gasoline won't evaporate. Make sure the end of the hose is under the liquid in the jar.

Mark the level in the jar and come back later. If the jar has more fuel in it that it did before it is seeping, and can allow carbs to keep overflowing until the tank is empty if they have a weak needle valve.

With a tight petcock the level of the fuel should not rise at all.

Just curious, why does matter if the fuel line stays submerged or not in the jar? Wouldn't it leak either way, if the tank fuel gets past the diaphram?

[MisterCinders]

Thanks tkent. I recalled that you had some petcock leak test but didn't remember the details.

[tkent02]

Just curious, why does matter if the fuel line stays submerged or not in the jar? Wouldn't it leak either way, if the tank fuel gets past the diaphram?

The reson for having the jar a few feet below the tank, is to create a syphon to help pull fuel through the petcock. More suction makes a better test. The longer the vertical drop between the level of fuel in the tank and the level of fuel in the jar, the more suction. And no Chuck, the size of the tank does not matter, only the vertical distance. To make a syphon, the hose must be full of fuel, and the end must be below the surface for the fuel to stay in the hose.

If the tube comes out of the liquid in the jar, the fuel will run out of it the tube, and you lose the syphon effect of having the jar a few feet below the level of the fuel in the tank.

Remember there is a syphon going on when the fuel line is attached to the carburetors, too, although it's not as far down.

If it doesn't seep any with the jar a few feet down, it certainly won't leak with the 16 inch or so drop when it's on the bike attached to the carbs.

[gsgeezer]

Petcock tests always indicate a Pingel, for me!