Topic: Changing over to Vacuum operated??

[LoopsAndLogic]

Since the weather is starting to break here in Ohio, I'm rushing to get my 400F ready for the riding season.

But after taking a spare petcock that I know works (1980 GL500) to put onto my 400F's tank,
 I noticed that the threads are the same size, but the GL's threads are fine, where as the 400's
is course.

Is there anyway to get my threaded nut onto the GL's fuel valve??

Does anyone know of a Vacuum operated petcock that has the same threads??

Maybe a CB750F???

I could really use the help, as this add-on was my plan for the entire winter

Cheers

LL

[GammaFlat]

I think a vacuum operated petcock is a great idea for these bikes.  Every time I think about it, I am stopped by the notion of "what happens when you get low on gas?"  The reserve concept works on these bikes and those bikes that have vacuum operated petcocks usually have a gas gauge (including Yamaha Razz scooters... hmmm, there's a place I can steal a gauge).  hrumph.

[GammaFlat]

now we're talkin'

[detdrbuzzard]

my nighthawk 450 has a vacumme operated petcock also but it still has the stop, on and reserve settings

[fuzzybutt]

the xs850 has a vacuum operated petcock that has the same spacing for the screws that the earlier cb750's had, when they fastened with 2 screws.

[BeSeeingYou]

I think a vacuum operated petcock is a great idea for these bikes.  Every time I think about it, I am stopped by the notion of "what happens when you get low on gas?"  The reserve concept works on these bikes and those bikes that have vacuum operated petcocks usually have a gas gauge (including Yamaha Razz scooters... hmmm, there's a place I can steal a gauge).  hrumph.

Yamaha used vacuum petcocks on the XS650 from 78-85 and I am sure on other bikes too.  They have three positions, on, prime, and reserve.  Prime allows a continous flow of fuel and is only used to fill the carb after the bike has sat long enough for the fuel to evaporate.  Reserve works the same as any other petcock.  In the on position fuel only flows as long as the bike is running and becomes in effect the off position when you shut down.  Having lived with them for 29 years on my XS650 I can say that I really like them.  In this time I have rebuilt mine twice, replacing the O ring and whizzer valve.  I still run the original vacuum diaphragms.  I have never been a big fan of non-vacuum style petcocks because if you forget or just get lazy you are relying on the needle valve to shut off the fuel flow. 
I am not as familiar on this point about Hondas.  Which models and years have vacuum petcock?  I am about to get my hands on a 76 750F. 

[eurban]

My experience with the factory vacuum operated fuel safety device (an inline fuel valve that only allows the flow of fuel from the tank to the carbs when vacuum is applied) on an 81 CB650 was that it made starting an extra long procedure with no provision for priming and caused fuel starvation issues when it began to fail.  I removed this critter and starting was quicker.  I am in the habit of turning off the petcock when I shut off the bike and don't miss the vacuum device at all. 

[Alan F.]

My 92 750 Nighthawk has a vacuum operated petcock, it threads onto a threaded bung on the left side of the tank.  Sound familliar?

91-03 were identical

[Soos]

The CB650 uses an automatic petcock (vacuum opperated) that goes inline between the original petcock on the tank and the carbs. You only ever have to touch your tank petcock to switch to reserve, or, turn it off to remove the tank.

But only on the CV carbs...


l8r

[BeSeeingYou]

Yamaha vacuum petcocks from a 79 XS650.  These are a right and left versions and there is also a  version with a 90 degree fuel outlet.  Hole spacing is 45mm and they use a 6mm 10 pitch machine screw threaded into the tank. No threads on the petcock itself so a different screw could be used.  They take the vacuum feed off the carb boot.  Rebuild kits for the rubber parts and diaphragm are readily available.

[LoopsAndLogic]

Guys, I need to know which one has the same threads....fine or course???

Can anyone take a snap shot of there threads on there CB650?? Or 750??

I know this is a lot to ask for, but the junk yards what big $$$ which is bull, and
any ebay seller won't waste his time.

Kinda in a pinch now.....

 

[LoopsAndLogic]

bump...

[Alan F.]

Sorry dude, the NH is put up for the winter with a full tank... but the threads looked like later model sohc4 if I had to guess.  Maybe Pingel makes a petcock that's threaded correctly?

[LoopsAndLogic]

Whats Pingel??

Thanks

LL