Topic: Vacumn operated fuel switch

[Goatman]

More questions from the rookie

I have a 82'CB650SC there is what appears to be a fuel safety switch that is operated by the vacuum from # 3 manifold. Is this just overkill on Honda's part to compensate for people forgetting to turn off the fuel?? or does it do something else? Mine seems to work OK, but it takes a little while to start after it sits for a week or so. Just trying to eliminate things that may leave me stranded.

Thanks in advance for the help

[mgbgt89]

I've got the exact same bike. I don't know if i would eliminate it, But maybe just replace the vacuum line that runs to it.

Lets see pictures of your bike? Black or blue?

[Goatman]

Mine is Blue, purchased from a family member for $700.00. Had to rebuild the Carbs as the bike had not been ridden much in the past 5 years or so. Put about 1600 miles on here since the rebuild (thanks to all the info on this forumn) I actually got all the pcs. back together.

[BVCB650]

Doesn't that have something to do with the CV style carbs, I was just reading something about that the other day on here.

[Goatman]

Not sure about that?? It appears that it is a switch that controls the fuel flow from gas tank to manifold that distributes fuel to the float bowls. Since it is a vacuum operated switch is it just an on and off thing ?

[BVCB650]

That I don't know cause I have a 79, but I know those style carbs work off of vacum in some way different than mine.

[Gordon]

More questions from the rookie

I have a 82'CB650SC there is what appears to be a fuel safety switch that is operated by the vacuum from # 3 manifold. Is this just overkill on Honda's part to compensate for people forgetting to turn off the fuel??

Yes it is.  You can safely and easily get rid of it (and all of the problems it can cause) and just remember to turn off your petcock when you park. 

[w1sa]

Yes it is.  You can safely and easily get rid of it (and all of the problems it can cause) and just remember to turn off your petcock when you park. 

+1
I have an '81 900 with similar arrangement.
If not used for a week or two, and to avoid loading the battery and starter, I often had to remove the fuel line where it distributes to the carbs and prime/fill the carbs directly.

[eurban]

Listen to Gordon; don't get confused by all the earlier posts! The object is a vacuum operated fuel safety device (call it VOFSD if you like).  It is designed to keep fuel spills from happening while parked or in an accident.  Fuel will only flow when vacuum (engine is cranking/running) is applied to the unit thus if a float hangs open or isn't sealing properly you won't end up with the contents of the fuel tank on your garage floor.  It was likely a govt mandated safety feature. . . .Remove it and your carbs will function just fine, and the engine should require significantly less time to crank over after longs periods of being unused.  If you remove it, you should always shut fuel off at the petcock when parked.  Also make sure that your petcock actually stops the flow of fuel in the off position. Oh and make sure to plug the vacuum hose that goes to the unit. . . .

[BVCB650]

I wasn't confused.

[Raul CB750K1]

FWIW, my modern GZ250 had a vacuum-operated petcock. Its smaller sibling, GZ125, has a "classic" petcock. I ended up changing mine for a "classic" one just because the rest of my bikes have the same, so I have already developed the habit of shutting the petcock off.

In the GZ250 petcock there is no "off" position, as it is in that position as long as the engine is not running-cranking. There is an "ON" position, there is a "RES" position -their names speak for themselves" and there is "PRI" position, that opens the petcock without the need of vacuum. That is used to prime the carb in the cases you have mentioned, when the bike has been sitting for some time, in order to fill the carb bowls and avoid that the first cranks waste battery energy because the carbs are not ready yet.

[jeepster]

I just thew mine in the trash today. Instead of having a random, useless hose flopping around on the carbs I am just going to seal it up with a new vacuum plug. (props to JTB)

[Goatman]

Thanks for the input, I will remove this contraption B4 my next ride

[vames]

Don't forget to plug that vacuum line.