vacuum petcock conversion - did I do it correctly?

[sacruickshank]

The fragile metal doodad inside my '81 GS550T vacuum petcock, the one that pushes out the plunger when in PRI, got mangled on disassembly. I prefer manual petcocks and couldn't find step-by-step conversion instructions, so I "guessed" with some hopefully logical assumptions.
My process was:
1. remove the front pieces of the petcock
2. remove mangled doodad
3. Unscrew four screws on back panel, carefully remove diaphragm, and then remove the spring that pushes the plunger to shut off flow when engine is not running
4. remove the oring from the plunger to let fuel flow whenever the plastic insert's holes line up with the holes in the petcock's body
5. reassemble the back portion of the petcock leaving out the spring and oring mentioned above
6. on the sheetmetal face clip, grind off the nub that keeps the petcock lever from turning to locations it wasn't originally designed to turn
7. reassemble the front portion of the petcock.
8. put a rubber stopper over the vacuum port

If I understand the design correctly, the petcock should operate as normal for the ON (South) and RES (West) positions. OFF will now be at the NW position.

Does that sound correct?

For reference, my petcock is this model
PXL_20220412_184237528.jpg

[dorkburger]

https://www.thegsresources.com/_forum/forum/technical-forums/carb-fuel-exhaust/79268-converting-a-vacuum-petcock-into-a-manual-petcock

[sacruickshank]

https://www.thegsresources.com/_foru...manual-petcock

thanks, my bike is an '81, so the petcock is a different model than the one in your link. Added a pic to the original post.

[Gorminrider]

There's been a couple of threads on this..here's one I just copied the text and it worked for several people...basically the "tab" is filed off the plate so the lever can be turned up.

"By removing the little stop tab so the lever can be straight up I have OFF. By removing the diaphragm o-ring I have ON (without needing vacuum) and still have a functioning RESERVE when in the RESERVE position. PRIME is no longer needed since vacuum is not connected. The filter screen is connected. I also added an inline filter to keep the fine rust dust from the carbs. I did leave the diaphragm spring out but you can do what you want. "

(I read somewhere that if the stop tab is removed so the petcock lever can be put pointing up it serves as an off. With the diaphragm o-ring removed fuel should flow as if vacuum opened the port. With the vacuum port plugged on the petcock to (stop the leak), the carb vacuum port plugged, the reserve position should work. When in the ON position fuel would flow, straight up position the fuel would be shut off.) "

BUT my addition to this is: it doesnt work on all my petcocks... it doesn't work where there is a hole right through the nylon plug that is being turned but it does work where there is one hole that flows into a hollow nylon plug...(the "tab" mentioned is on the chromed cover plateiremoving it allows the tap handle to rotate 360 which in turn rotates the (nylon?) plug that directs gas...

Also tap lever MIGHT hit the tank in some cases .

[sacruickshank]

There's been a couple of threads on this..here's one I just copied the text and it worked for several people...basically the "tab" is filed off the plate so the lever can be turned up.



BUT my addition to this is: it doesnt work on all my petcocks... it doesn't work where there is a hole right through the nylon plug that is being turned but it does work where there is one hole that flows into a hollow nylon plug...(the "tab" mentioned is on the chromed cover plateiremoving it allows the tap handle to rotate 360 which in turn rotates the (nylon?) plug that directs gas...

Also tap lever MIGHT hit the tank in some cases .

My nylon plug has the hole that goes all the way through, which is why I suspect the NW position (and maybe the NE) is the position where the neither the ON nor RES outlets will line up with the hole in the nylon plug. I'll add a pic later today

[Gorminrider]

Yes, I suspect yours won't work with the method explained then. But there's other ways to convert a vacuum petcock I expect. (Beyond a few tests for interests' sake, I haven't bothered to really work on it. I like my vacuum taps.)

[Gorminrider]

I guess the first thing to know in the petcock design is that there's no OFF without the spring pushing the plunger with its o-ring in- (the default without vacuum to pull it out......)Prime works because the nylon barrel has that brass thing behind it that it turns to push back against the plunger and spring...no vacuum required for fuel to flow.....The nylon barrel's job is just to direct fuel from Res or Run...
But the mod above uses the nylon barrel instead of the plunger-oring-spring by turning a single hole in the nylon barrel completely away from either RES or RUN when OFF is wanted. But if your nylon barrel happens to have the hole straight through it (both sides) one side of it will always allow fuel to flow.