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For those interested, I've found a way to modify the stock vacuum tap to give an OFF position and do away with the troublesome vac operation.

I'll describe the basic here but I'm going to link the whole thing on imgur if I can. This is for the ZRX 1100 tap

1; Take the back off the tap exposing the rear view of the casting.
2; See the keyhole-shaped recess where the o ringed plunger seats in the tap.

3; Fill that recess with epoxy paste/silicon ensuring you don't go deeper than the recess or above the rear face. Don't fill in the actual drilling passageway just the depth of the seat. This blocks that port.

4; Look at the front tap lever, remove the lever holding plate, see the small tab/flag and file off the tab.

5; Remove the plastic knob from the tap front, see the locating boss has 3 flat faces and 1 slightly curved face. This locates the knob in one direction. File the curved face down to flat so the knob fits 180 degrees from original.

6; Refit knob and tap front with plate. Mark the plate at the 3 O'clock, 6 O'clock and 9 O'clock positions if necc with a dab of paint.
7; With the new knob position turning the tap to 9 O'clock gives you ON, 6 O'clock is OFF and 3 O'clock is RES. There is now NO Prime position.
8; Turning to the back of the tap, make a gasket of suitable material to cover the rear face and secure with the original cast plate, leaving out the vacuum diaphragm.
9; Plug the original vacuum line or cap the inlet manifold as this is now redundant.

You will be able to rotate the tap 360 but if you stick to the 3 positions it should function like a non vac tap.
I can't say whether it works on all K vac taps but a bit of investigation by the owner may reveal a similar solution.
 

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I'm following this thread with great interest because I too am getting REAL sick of seeing a puddle of gas in the catch-basin I put under the overflow tubes on my KZ650. My OE fuel tap is the 'top-hat' variety, which ostensibly uses a rubber cone to stop the flow of fuel from the tank. But it doesn't. And they apparently don't make them, or the parts, anymore.

Does anybody know what everybody else is using/has substituted for a non-leaking petcock? I'm thinking a straight manual one would be good as I have gotten in the habit of turning off the petcock of every bike I have when I stop. Do the K&L petcock kits on Ebay work? I like the convenience of a vacuum-operated petcock, but am rather loathe to pay $50 for an On/Off/Reserve petcock with two simple plates.

Is ther a regular, standard petcock that you can just bolt on? Dartmoor Dave, you wouldn't happen to have made a picture tutorial for that above procedure, would you...?
 

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I bought a service kit off eBay which worked well but I’ve never had a problem with fuel leakage.

If I had that problem, the first thing I’d check is the floats and float valves in the carbs. Fuel shouldn’t be able to get past the valve when the bowl is full and shouldn’t therefore overflow.
 

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That's a very good point - but I believe my carbs are spot-on, after having redone them three times when I was resurrecting the bike. The bike runs great, idles great, etc., but I have noticed after I come back from a run they're fine - come back a bit later and there's fuel dripping sporadically out of the overflow tubes, usually the #1 / left side of the bike. I don't think that would happen if the vacuum-operated petcock was sealing. "Six of one, half a dozen of the other", as they say...

What you say is correct, it shouldn't be leaking but even after a bench-test to check to see if the floats are shutting off the fuel (they do), I still get fuel occasionally dripping out of the overflow. Yes, its maddening. The pilots are snug, the needles are fine, the floats are shutting off the flow of gas when I manually operated them on the bench...but also these vacuum petcocks have a history of leaking, so be it as it may I'm going to go to a manual one and see if that helps. Yes, if it still happens then I have obviously overlooked something, but I have the original 'top hat' vacuum petcock, and that top-hat was looking kind of scrunched when I took the petcock apart to try and fix it, and changing the oil every two days or so gets rather old, and expensive. And of course they don't make that/those parts anymore.

FWIW, I was looking around online and there's a guy on Ebay who is offering a (pretty ugly) manual petcock with an adapter plate and gasket, for $50! I looked around, and a decent petcock online is about $20, and Lowes sells a 1/4" x 2" x 3-FOOT piece of aluminum for $8. It will be a simple matter to chop that aluminum piece into MANY adapter plates and fit that $20 petcock to it, which is what I hope to do and see what happens. It would be simple enough - drill/countersink the M6 mounting holes where they should go and drill/tap the larger center hole for the petcock, cut out a gasket and BOOM! $28 and a little work. We'll see what happens.
 
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