Turning off Gas

[5th_bike]

Originally Posted by alantf

There is no such thing as a "non vac petcock".

Sure there is, my 50 cc mopeds had a non vac petcock "on" and "off". No reserve as far as I remember.

The 35 cc Solexes didn't have a petcock at all. The gas just got vacuumed into the carburetor and flowed back when the engine went off. They also didn't have a float with needle nor associated problems.

[alantf]

What I meant was that a "petcock" is vacuum operated. If it's not vacuum operated it has another name. I agree that if it's the old type, that was just a manual switch, then yes, I always used to switch off whenever I turned the engine off. I always got into the habit. But, offhand, I didn't know that there were any modern bikes that still had the old type. Even the geezer, which is just about the cheapest bike on the market, has a vacuum petcock, so it seems that the instructor is years out of date, or just plain & simply doesn't know what he's talking about. Perhaps you could ask him to name any modern bike that uses the old system, to see how extensive his knowledge is.

[geezer]

so if its not vac its not a petcock? ok let me go tell everyone i know this new bit of info :lol: anyway if you werent aware most people with vacuum petcocks tend to delete the system all together due to age and diaphrams going out, like on my old 83 midnight maxim. i converted cause fuel was leaking. lots of harley riders also swap due to theres being unreliabe. so here in america only i guess the valveswithnoname i shall refer to them as now are still very alive and kickin

[blaine]

Originally Posted by geezer

so if its not vac its not a petcock? ok let me go tell everyone i know this new bit of info :lol: anyway if you werent aware most people with vacuum petcocks tend to delete the system all together due to age and diaphrams going out, like on my old 83 midnight maxim. i converted cause fuel was leaking. lots of harley riders also swap due to theres being unreliabe. so here in america only i guess the valveswithnoname i shall refer to them as now are still very alive and kickin

I would buy a rebuild kit,before I ever reverted to the old style of petcock.(also cheaper) Harley had a known problem with their vacuum petcocks,because the high vacuum of the engine,kept rupturing the diaphram's in the petcock.

:cool:

[FutZ]

petcock - regulator consisting of a small cock or faucet or valve for letting out air or releasing compression or draining
regulator - any of various controls or devices for regulating or controlling fluid flow, pressure, temperature, etc.

A petcock is still a petcock with or without vacuum. The only difference is a spring loaded diaphragm that will engage when vacuum is lost to prevent flow.

Off=Off
On=Flow if Vac Present or on Non-Vac flow until the float stops it.
Pri=Flow until the float stops it.
Res=On, but uses a secondary inlet that is lower in the tank

On non-vacuum operated, if your float sticks due to lack of maintenance or if it is not adjusted correctly it can fill your engine or go out the carb overflow and leave you stranded. Hence the repeat warnings to “turn it off” as a good habit. This can also happen on Vac operated but only if the diaphragm or spring fails at which point it’s time for new parts and there was nothing you could do to stop it.

If you have an off, use it. It is easier than walking. If you don't have an off (GZ standard is vacuum operated), for the purpose of this forum make sure it is set to On until you run out of gas.

[geezer]

bravo good sir :2tup:

[savrip]

EKG! Sorry I had that screamed at me all weekend.

E-Engine Shut-off
K-Key Off
G-Gas Off

Generally this was for the older bikes, but they teach it to you because it's good to know, and they don't know what type of bike you're riding in the future.

[tulsawalk]

MSF instructor here. I'll take a shot at clearing the mud on fuel valves:

Fuel injected motorcycle = no fuel valve

Gravity fed carburetor = On / Off / Reserve - In the on position the fuel simply gravity feeds from the tank as long as there is fuel. If you have this type of fuel system you always want to turn the valve off when the motorcycle is not running because the needle and float is the only thing keeping the fuel from flooding the carburetor, cylinders and then crank case. If the needle and float fail you have the chance of hydro locking the piston and bending a connecting rod and/or filling the crank case and diluting your oil with gasoline.

Vacuum fed system such as the GZ250 has = On / Prime / Reserve - In the on position the fuel will not free flow to the carburetor. It depends on intake vacuum to open a valve in the fuel shut off valve to allow fuel to flow. The prime position is just what it sounds like. If you bike has been parked for some time it allows fuel to free flow to the carb until the bowl fills and the bike starts. Once started the valve should be returned to the on position. You should never have to use the prime position unless the bike has sat for a time.

The reserve position is just that. It allows you a few more miles to get to a station if you run out of fuel. Of course if you forget to return the valve to the on position after filling up you no longer have the advantage of the extra fuel.

[Gz Rider]

...

[jonathan180iq]

I think the question here is: "Are there any bikes made in the last 20 years that have gravity fed petcocks that require being turned off? Do the manufacturers recommend using off, unless you are performing some type of maintenance?"

Cause, uh, I don't know of any. And of the bikes that I've owned that had the "OFF" option, there was never any reason to use it, unless I was going to remove the tank.

And if there are none, then why do we continue teaching to turn then off?