Turning off Gas

[birdmove]

This confusion on gas "petcocks" can be excused due to the fact that very new riders may never have been exposed to the earlier petcocks that were , and are, gravity fed, engine vacuum having nothing to do with fuel supply on those bikes. Since I'm 57 years old and started riding at eight, almost every motorcycle I've owned has had a gravity fed petcock. With the gravity fed one must develope the habit of twisting the lever on the petcock to the off position when parking the bike. The reason being, that if the needle and seat develope a leak, possibly due to a little piece of dirt, the gas will continue to fill the float chamber, and then will overflow and continue leaking.

But, don't get the idea that vacuum controlled petcocks are trouble free-they most certainly are not! Check that subject of a Suzuki DR200 thread at, say, advriders.com, and you will see that the vacuum petcocks are known to develope leaks and fill the cranckcase with raw gas. Many owners of those bikes replace the vacuum petcocks with gravity ones and simply turn them off when parked. Many DR200 owners even replace the OEM petcock with a gravity fed before any problem developes. Dual sport bikes are often way off the beaten path and owners need to be pretty self sufficient-many dual sport riders are set up to fix a flat on the trail, because noone is going to find them and haul their bikes out to the road.

I prefer a gravity fed petcock any day due to simplicity-just turn it to off when parked and you won't have a problem. The Royal Enfield Bullet still used a gravity fed petcock right up until the new fuel injected model came out. There are other motorcycles still using the gravity fed units also.

Jon

[mole2]

Originally Posted by jonathan180iq

I agree that the point is valid. It's just dated.

And like you said, if people are riding around with faulty fuel control valves, then they have bigger problems than simply remembering to turn the petcock to "off".

The generalization that all "modern" petcocks are vac operated is untrue. I just looked at my 2009 carb V-Star 650 and my neighbors 2007 carb V-Star 1100 and both do not have a vacuum line to the petcock. They both have electric fuel pumps which draws the fuel. Hence the petcocks are flow valves with Off - On - Reserve. Teaching AND utilizing the "turn the petcock off" (on bikes/petcocks that have an off position) is very applicable to bikes made today.

[alantf]

Originally Posted by mole2

They both have electric fuel pumps which draws the fuel.

So they're both fuel injected, as opposed to carb, right?

[mole2]

Originally Posted by alantf

So they're both fuel injected, as opposed to carb, right?

No, they're both carb.

[blaine]

Originally Posted by mole2

The generalization that all "modern" petcocks are vac operated is untrue. I just looked at my 2009 carb V-Star 650 and my neighbors 2007 carb V-Star 1100 and both do not have a vacuum line to the petcock. They both have electric fuel pumps which draws the fuel. Hence the petcocks are flow valves with Off - On - Reserve. Teaching AND utilizing the "turn the petcock off" (on bikes/petcocks that have an off position) is very applicable to bikes made today.

Typically the pump has a built-in pressure-relief valve to keep it from oversupplying the float bowls. When the float bowls fill up, and the float needles rise into their seats to cut off the flow of gas, the pump senses this rise in pressure in the fuel line and stops momentarily starting up again when the pressure in the line drops.

The pump is often connected to the engine's ignition system so that it doesn't pump unless the engine is actually turning over. This prevents the pump from working in case the bike falls over and the engine dies but the ignition is still on. In many Hondas, for example, the pump is connected to a fuel cut-off relay that is in turn connected to the ignition control module. The relay prevents battery current from getting to the pump unless the ignition module is transmitting ignition pulses to the relay indicating the engine is running. No ignition pulses, no current to the pump.
:cool:

[Water Warrior 2]

On the Vstrom with fuel injection there is a tip over sensor/relay that will shut off the fuel pump if the bike takes a nap. Probably quite a common safety feature on many bikes.

[mole2]

Originally Posted by blaine

Typically the pump has a built-in pressure-relief valve to keep it from oversupplying the float bowls. When the float bowls fill up, and the float needles rise into their seats to cut off the flow of gas, the pump senses this rise in pressure in the fuel line and stops momentarily starting up again when the pressure in the line drops.

The pump is often connected to the engine's ignition system so that it doesn't pump unless the engine is actually turning over. This prevents the pump from working in case the bike falls over and the engine dies but the ignition is still on. In many Hondas, for example, the pump is connected to a fuel cut-off relay that is in turn connected to the ignition control module. The relay prevents battery current from getting to the pump unless the ignition module is transmitting ignition pulses to the relay indicating the engine is running. No ignition pulses, no current to the pump.
:cool:

Which means turn the petcock to the off position when you turn the bike off. :biggrin:

By the way, the fuel pump comes on as soon as you turn the key on on the V-Star to pressurize the system. It does not work off of ignition pulses. That means the pump is live as long as the key is on. This means you must turn the key off as well as turning the petcock to the off position when parking the bike. I am sure many other bikes work this way.

[mole2]

Originally Posted by Water Warrior

On the Vstrom with fuel injection there is a tip over sensor/relay that will shut off the fuel pump if the bike takes a nap. Probably quite a common safety feature on many bikes.

I wonder if they have that on the Stars. I'll have to research that. :biggrin: I know they have it in cars and boats.