Never heard that before. I thought it was a vacuum petcock that would not leak fuel down when there was not vacuum from a running engine present. It was a safety measure in case the float valve failed and then fuel would end up on the floor and in the crankcase.
I part out bikes and sell used parts, and have owned a few Sabres to ride....somebody fed you a line. The fuel is fed to the carbs like your lawn mower, by gravity. The vacuum line to it...is as I explained. There is no need for a fuel pump. Do some research or check your repair manual. Petcocks on the Sabre VF750S and VF700S were the same from 82 to 85. They are obsolete even though they are still listed on cycle sale sites parts fiche diagrams and price lists. The part would come from Honda and there are none available. You would be very lucky to find even a NOS part now.
You can get the petcock rebuild kits on ebay all day long for around 20 dollars. Or you can do like I did and bypass the vaccum operation and make the petcock function like others. and it's much cheaper than the rebuild kit.
You can buy fittings to adapt to fit any size petcock and just delete the vaccum altogether for a lot cheaper. Unless you just have to go back stock. I still say if you have to have stock buy the rebuild kit.
I want to resurrect this thread. I have a vf700s, I just replaced the fuel petcock from another bike, everything looks still in decent shape and it doesn't leak, however, the vacuum line I have disconnected and sealed off. This was how the other leaky petcock was setup too. Now, when I drive, I get about 45 - 70 miles and I start to die out and have to switch to the reserve setting. I go to fill up again, and i'm only putting in about 1.5 gallon (out of 5 gallon tank). Does this sound like this petcock acts like a low pressure pump? or least drawing out fuel from the tank when the tank level hits a certain level???
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