Remove vacuum requirement for Petcock - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 41 (permalink) Old 04-14-2013, 10:12 PM Thread Starter
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Remove vacuum requirement for Petcock

Got a quick question. Rather than pay $35 for a petcock rebuild kit or use a different petcock which needs anouther outlet added (what Wolffie did) can I simply plug the vacuum line from the front carb and slightly modify the vaccum diaphram in the petcock to allow it to flow fuel without vacuum?
My petcock vacuum diaphram doesn't work well on the starter (engine shut off from no fuel, new battery, spins fine) I've replaced the line from the carb using good clamps and a vacuum gauge shows the vacuum from the carb is probably fine (the needle really jumps so it's hard to read). I've gotten stuck twice now when I didn't get the reserve flipped fast enough. Sucking the vacuum line to the carb for a minute gets the bowls refilled.
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post #2 of 41 (permalink) Old 04-15-2013, 12:39 AM
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Originally Posted by FoolAmI View Post
can I simply plug the vacuum line from the front carb and slightly modify the vaccum diaphram in the petcock to allow it to flow fuel without vacuum?
That seems to be the real question here that a few (including Wolfie) have been asking recently.

At this point, we just need someone to simply test this out to see if it works.

......I'd rather wake up in the middle of nowhere then in any city on earth.

*2014 VN900 Custom (16,200 miles and counting)
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post #3 of 41 (permalink) Old 04-15-2013, 01:12 AM
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Adding the TW200 petcock was super simple. Simpler than rebuilding the stock one.

1985 VN700 unknown mileage (over 33K)

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post #4 of 41 (permalink) Old 04-15-2013, 02:25 AM
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Adding the TW200 petcock was super simple. Simpler than rebuilding the stock one.
As soon as I can locate an appropriate "T" fitting, I'll be putting my TW200 petcock on. May do it same time (or shortly after) I do my ear shave. It's just that time of the year now where I don't want to rip into anything because I'd rather be out riding

......I'd rather wake up in the middle of nowhere then in any city on earth.

*2014 VN900 Custom (16,200 miles and counting)
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post #5 of 41 (permalink) Old 04-15-2013, 03:13 AM
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Originally Posted by Ndr View Post
As soon as I can locate an appropriate "T" fitting, I'll be putting my TW200 petcock on. May do it same time (or shortly after) I do my ear shave. It's just that time of the year now where I don't want to rip into anything because I'd rather be out riding
Search eBay using the words "1/4 fuel T fitting" and you'll see a bunch of them in different materials. If you want to buy it locally you can still do the search anyway to see which you want to look for.

1985 VN700 unknown mileage (over 33K)

AGM Battery
Iridium spark plugs
NGK wires and caps
Relocated R/R
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post #6 of 41 (permalink) Old 04-15-2013, 05:03 AM
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That seems to be the real question here that a few (including Wolfie) have been asking recently.

At this point, we just need someone to simply test this out to see if it works.
Yes, it will work. Even though I have never had a Kaw petcock apart, I have had others. They are all simple devises that must necessarily act in the exact same manner. The exact same principals apply to vacuum/boost referenced fuel regulators.

I have not been inside a VN petcock, but this is what you will find.

Vacuum overcomes a spring (compresses), and pulls the diaphragm toward the vacuum side. In the middle of the diaphragm directly opposite the spring will be a protrusion/fuel obstruction. To eliminate vacuum control, remove the spring and shorten the protrusion on the opposite side of that spring. If the protrusion provides a 'seat', simply removing the spring/disconnecting the vacuum source will remove vacuum control. If the resulting fuel delivery is insufficient, find a spring with a slightly larger diameter than the protrusion and install it on the gas side of the diaphragm using the protrusion as the spring guide. You quite possibly could remove the spring and just turn the diaphragm around. Install it backwards.

You will now have reentered the 1970's, and must (for safety's sake) turn the petcock off anytime the engine is not going to run in the short term.

I may eventually do this to mine. HTH.

Edit. You could also just install a check valve in the vacuum source hose. This would maintain a constantly high vacuum to the petcock. Available at auto parts stores, these should cure virtually all issues. You would still have to constantly turn the petcock off when not in use.

Last edited by wmsonta; 04-15-2013 at 05:26 AM.
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post #7 of 41 (permalink) Old 04-15-2013, 07:46 AM
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Your biggest issue with any gravity fed petcock is to remember to turn it off at the end of a ride.

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post #8 of 41 (permalink) Old 04-15-2013, 03:36 PM
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My local hardware store had the T fitting...$1.25
I been scratchin my head for days trying to remedy the stock one. More work than its worth IMO, but CAN be done, definitly with one of the older ones with "prime"...Prime becomes "on", then where the "on" is now, the orifice would need to be closed off to become the "off"...really not worth it IMO since the TW200's can be had for $14...
Some guys switched to Pingels, but they cost more and dont believe are bolt ons...



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post #9 of 41 (permalink) Old 04-15-2013, 03:48 PM
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Your biggest issue with any gravity fed petcock is to remember to turn it off at the end of a ride.
Why?

Just wondering because I have an old atv I am working on, gravity fed petcock.

I also have many pieces of gravity fed equipment.

thanks for the info, ken
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post #10 of 41 (permalink) Old 04-15-2013, 03:49 PM
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fyi the VN800, has reserve, prime and on in that order, starting with the knob facing up.

kenny
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