Possible petcock fix?

[Kingjoel]

The petcock on my 1978 GS 1000 leaks fuel through the vacuum diaphragm. Fuel is sucked into the vacuum port on carb #3. 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. Is my thinking flawed?

[chris]

Is it possible? I say yes, because I did it , but I can't tell you how because it was more than 30 years ago. My stock diaphragm failed on my 83 1100e , the bike was less than 5 years old. The engine filled with gasoline. I did not want to buy a new petcock so I converted it to a
manual petcock by plugging up some ports. If I remember correctly, off was the old on position and on is the old reserve position. I ran the bike like this for over 20 years and never had a petcock problem again. These days I just run a pingle duel outlet with reserve, which I am very happy with.

[Big T]

Yep, except you shouldn't have to alter the petcock. Just cap the vacuum port on #3. Then, use Prime for ON and you don't have reserve

[Kingjoel]

The way I tried to explain you would have an Off and still have a reserve. The most important would be the OFF position.

[salty_monk]

I want to say I agree with your thinking. Hard to say for sure without one in front of me. Pretty easy to test, you don't have a lot to lose to do some bench testing if it's knackered already.

Note that filing the tab & turning it all the way around does work but you'll need to mark the position to off as sometimes it's not straight up and does leak. I'd make sure you have good float needles that can hold the fuel back on their own if I was going to do this.... (also in case you forget to turn it to off).

[rphillips]

Just wondering if there's a reason to modify this one instead of just fixing it? Rebuild kits appx. $12. Some here have had problems rebuilding them, but so far I've rebuilt at least a half dozen with no problems.

[chris]

Yep, except you shouldn't have to alter the petcock. Just cap the vacuum port on #3. Then, use Prime for ON and you don't have reserve

Easier, but you lose about 4 liters of tank capacity

[Steve]

Easier, but you lose about 4 liters of tank capacity

How would you lose capacity?

Yes, you lose the REServe function, but the PRIme draws off the bottom of the tank, so you can use it all (with no REServe).

.

[mrbill5491]

The petcock on my 1978 GS 1000 leaks fuel through the vacuum diaphragm. Fuel is sucked into the vacuum port on carb #3. 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. Is my thinking flawed?

Just buy a new one and go ride. I've learned my lesson over the years, once it starts acting up, stop the fretting, stop the over thinking, just buy a new one.

[sam000lee]

In the straight up position it would act as an OFF position, regardless of the condition of the vacuum diaphragm/o-ring. You could use PRI as "on", which would draw from the "reserve" bottom of the tank and Straight Up as "off". Here are the different positions broken down:

Starting from the 12 o'clock position, I'm enumerating the ports on the petcock body:

1 - 12:00 - Top of petcock filter (regular gas inlet)
2 - 3:00 - Bottom of petcock filter (prime inlet)
3 - 6:00 - Through to the petcock outlet
4 - 9:00 - Blocked/Does nothing. Any other port "connected" to this is rendered "blocked".
5 - Center - flow actuated via vacuum - While open, gas can flow from the front to the back and out of the petcock outlet.

There are two slots in the petcock lever piece that each can connect two of #1-#5

On:
#1 <> #5 - Vacuum flow from top of petcock filter
#3 <> #4 - Does nothing

RES:

#2 <> #5 - Vacuum flow from bottom of petcock filter
#1 <> #4 - Does nothing

PRIME:

#4 <> #5 - Vacuum does nothing
#2 <> #3 - Un-interrupted flow between bottom of petcock filter and petcock outlet.

Straight Up:

#3 <> #5 - Vacuum actuated center connected to petcock outlet. Were the engine running, this would do nothing.

#1 <> #2 - Top of filter linked to bottom of filter - does nothing.

[Kingjoel]

It works perfect!! 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.

[rphillips]

Great info. Now if I decide I want to go back to the days when we had no auto. fuel shut-off & I needed to remember to turn the fuel off all the time I'll know how to do it. But for now I think I'll just keep the auto working. I don't need to waste any of the little memory I have left.

[Kingjoel]

The reason I did this is my 42 year old diaphragm was leaking fuel, getting sucked into the vacuum port on cylinder #3. I replaced the diaphragm and in the process lost the rubber gasket with the four holes (on the lever side of petcock). I replaced that four hole gasket with an old one from a cb 750 to get by (I have a new one now, less than $5 on Ebay). I had a massive leak so unintentionally I destroyed the o-ring on the new diaphragm (my brain slips to neutral at times). Not knowing the size of the o-ring or wanting to replace it with one that would leak after time I went this route. I've read where aftermarket petcocks are junk and non fuel resistant o-rings are used in the cheap kits. OEM petcocks are about $300 for this bike. I did not want to lose the RESERVE function by just switching the lever to PRIME. I have four other bikes without vacuum petcocks. I can remember to shut the gas off. I thought this method was better than buying a Pingle manual petcock as many have done. You guys are GREAT, I appreciate this forum. I hope this can help someone.

[rphillips]

Great to hear you've got it worked out.

[Gorminrider]

just a note but this "tab removal" for fuel OFF won't work for every petcock...for instance, not this one:
petcock part.jpg

..turning the pictured nylon piece with a hole drilled right through 180 degrees does nothing. Fuel flows...

However, some petcocks on Suzukis don't use this particular part... their oh-so-similar part is hollow with a single hole drilled to the hollow centre and it does work to turn fuel OFF when tab removed and tap handle turned up.