Hello all,
So, as some know, I have a 1998 gs500. I was driving from tally to jax one day on I-10 and all of a sudden,
buuuhhhhnnnnn pleh. bike dies
I thought, hmm, what has happened? It felt like an overheat, but the typical smell and feel of a overheated aircooled was not there. I looked into my newly installed filter- aha, there is no fuel here! by alas, my tank is full?

Long story short, 180 miles, 20 mile increments, loooong drive.

I find out later that the petcock is vacuum actuated and prone to sudden failure and fuel starvation. In order to get back to tally later, I dissected and rebuilt the petcock in a manner that gave me res-off-on function starting at the top of the throw. This never sat well with me, the fuel flow cut-off wasnt perfect, and i felt... bad... about it. Here is how I decided to remedy my own personal worries:

Step one, remove the offending petcock:


Step 2, finger out a way to route the new hoses, combine the twin hoses from the tank and install

^^ I used a 5/16" brass tee to couple the twin lines from the tank, which in turn flows to the petcock.

Step 3, attach everything together, simply bolt on the new petcock from a yamaha Vmax 700.




So, its all installed, and ready to go, I ran the bike up and down a closed rode a few times at WOT so see if the lines started to drain, but so far, so good. I modified the interior of the petcock so the interior diameter was larger to accommodate max fuel flow. with this setup, I lose my reserve function, which I never used either way. I always keep a quick eye on my mileage, so no worries on running out of fuel. These tanks are wantonly small either way.

This whole process took maybe an hour, including tinker time, and cost less than $15.00 (including the tee and petcock).

Any questions or comments, hate mail, feel free to post it. I want feedback, but if you hate this idea remember this; constructive criticism.

Peace,
Funderb

First, you could have put the petcock in PRIME. That overrides the vacuum and lets gas flow freely. Remember to set back to ON or RES when bike is off.

Second, since you do not use your reserve, you only need one line from the tank: the reserve like. The main line can be plugged up. There is no "reserve tank". It is only a difference in the height of the tube that lets gas out of the tank. Eliminate the "T" joint and just run one line from the tank.

It could be your vacuum like to the petcock came off or was pinched. Or the petcock went bad. Replacing the petcock would have been OK.

I have 3 GS500's. Never had that problem except the first time I rode Junior home on the freeway after buying him. Fortunately, I remembered the forum mentioned put on PRIME and I made it the remaining 45 minutes home at 75mph on I-5. It never happened again. It may have been bad gas or just that Junior hadn't been taken out for a good ride for a while. Didn't replace the petcock and he has operated correctly ever since.

People like to be vocal about the petcock failing. I think most of us have never had that happen. When something goes wrong - whenever it may be - that's when people are most vocal. They don't say anything when things are OK.

Hope you find this information helpful.

As for the PRIME function, i've found that the fuel flow is quite restricted, and couldnt support the remaining 2 hours of travel. The prime orifice is 1/8" about, or smaller, I found this on disassembly of the petcock unit.

In my case, I had a complete failure of the design, so I felt it needed to be remedied permanently. I could find no reason why, other than the obvious lower manifold pressure at highway speed.
(With the totally open exhaust, k&N and new jets, the bike is much thirstier than it came to me as stock. I'd say I went from 60 to 43ish mpg after the changes. Both driving conservatively, if I drop the throttle everywhere I go I imagine it would be much lower.)

Consolidating to one fuel line is pretty much what the tee does, though it is rather circular. I just felt bad completely closing one side off, i felt it would get sad dangling all lonely and closed off.

Anecdote:
I drive a car of a particular year and model (as most do) of which a small percentage have had catastrophic flywheel failures resulting in the transmission shearing off the engine. My clutch was starting to go bad and make a grindy noise in certain circumstances, but was fine, but I decided, what the hell, I'll yank that thing out of there and replace the clutch and flywheel and prevent unlikely but possible disaster. When I do things, I tend to do them all the way, but in a good way!

So maybe it is extreme, meh! I am glad to hear that this isnt as common a failure as the wide world of the internet seems to think. And thanks for the input, I will add it all to the useful info database.
And I may come to you one of these days if my slide block fails on me again!
Another +1 for adidasguy.

I applaud your ingenuity     Nothing below is directed at you but are just general thoughts and opinions.

I have owned lots of bikes with vacuum actuated petcocks over the years and I have only ever had two fail on me, a '93 Nighthawk 750 and an '89 GS500.  Both bikes were over 10 years old at the time which I think is a respectable service life for any part to last.  Both bikes got brand new factory petcocks and I never had another problem in the time I owned them.  Vacuum petcocks are just so much more convenient in my opinion, they take out the forgetful idiot factor that I am prone to.  Everyone gets annoyed when a part fails but you have to expect things to break on an old bike, it does not mean the part is inherently defective.  I have to agree with Adidasguy, there are so many posts bashing the factory petcock that any newb doing a forum search could easily come to the conclusion that it is a defective part.  My 2 cents...

-Jessie

How come every time I write a rant and go to post it I get the "Warning - while you were typing a new reply has been posted. You may wish to review your post."   

I too applaud the ingenuity.  Especially at such a low cost.   

Tally you say?  You wouldn't want to lend a hand on repairing a bike in Thomasville would you?  Hahaha. 

Maybe you had pinched lines or a fuel filter that was restricting fuel flow.
Most of us never have the problem and PRIME always solves it if the petcock does fail.
I see you have a fuel filter. Was that there before? Not all fuel filters work on a gravity fed fuel system.

adidasguy- that could be very likely, the fuel lines at the time were 12 years and 20k mi old. They have only recently been replaced. The filter I have on there is a simple perforated plastic thing, like a screen, (I can't imagine it's any better, really, than the tank screen) its biggest benefit is that it is a sump, a large area at the lowest point of the fuel flow. like a sink trap. I don't hate vacuum petcocks, I was just bitter that mine seemed to have failed. (my only evidence is that after removing the vac system, the bike never died again - circumstantial at best.)

haha, thanks for the applause, shonole and baltimore, I am a tinkerer by nature, and it shows on the bike.

and as for trips to thomasville, I used to play paintball up at blackwater paintball park all the time, and I do enjoy the 'zen' of working on pretty much anything, so if you're ever in a pickle or need a hand, i can always show up with PBR and some wrenches! 

Quote from: Funderb on January 25, 2012, 04:44:03 PM
Hello all,
So, as some know, I have a 1998 gs500. I was driving from tally to jax one day on I-10 and all of a sudden,
buuuhhhhnnnnn pleh. bike dies
I thought, hmm, what has happened? It felt like an overheat, but the typical smell and feel of a overheated aircooled was not there. I looked into my newly installed filter- aha, there is no fuel here! by alas, my tank is full?

Long story short, 180 miles, 20 mile increments, loooong drive.

I find out later that the petcock is vacuum actuated and prone to sudden failure and fuel starvation. In order to get back to tally later, I dissected and rebuilt the petcock in a manner that gave me res-off-on function starting at the top of the throw. This never sat well with me, the fuel flow cut-off wasnt perfect, and i felt... bad... about it. Here is how I decided to remedy my own personal worries:

Step one, remove the offending petcock:


Step 2, finger out a way to route the new hoses, combine the twin hoses from the tank and install

^^ I used a 5/16" brass tee to couple the twin lines from the tank, which in turn flows to the petcock.

Step 3, attach everything together, simply bolt on the new petcock from a yamaha Vmax 700.




So, its all installed, and ready to go, I ran the bike up and down a closed rode a few times at WOT so see if the lines started to drain, but so far, so good. I modified the interior of the petcock so the interior diameter was larger to accommodate max fuel flow. with this setup, I lose my reserve function, which I never used either way. I always keep a quick eye on my mileage, so no worries on running out of fuel. These tanks are wantonly small either way.

This whole process took maybe an hour, including tinker time, and cost less than $15.00 (including the tee and petcock).

Any questions or comments, hate mail, feel free to post it. I want feedback, but if you hate this idea remember this; constructive criticism.

Peace,
Funderb

That looks real nice ... I've done the same (except with components that look much less professional).

If my bike ever shuts down out on the highway, fuel flow restriction due to a faulty petcock will be one less thing to troubleshoot.

I'm looking to do this to mine, as my petcock is jacked.  I have no reserve, and this will be a much easier (and more affordable) fix.

Do you remember what parts you purchased, and from where?  Specifically the filter and coupling.  Also, what did you use for fuel line?  Tygon?

Thanks!

Its worth doing for peace of mind, if you're into that...

I got most of the stuff at the local discount autoparts. the tee is just a 5/16" brass tee,
The filter is a cleanable one, that flows very freely, and is in pretty much any auto parts store.
The fuel line is just your run of the mill alcohol resistant 1/4" hose, I wanted clear, so I could see any particulates.

As for the petcock, I bought it on ebay by searching "petcock" and looking for the cheapest on that might fit. It was about 8 bucks. I would recommend any petcock for bikes  250cc or over. Under that, you might run into fuel flow problems..

About 3ft of hose and a pile of hose clamps and you'll be off to the races.

I've been considering replacing my fuel lines with clear ones. What size did you use, just out of curiosity?

Quote from: Kijona on February 16, 2012, 11:09:16 PM
I've been considering replacing my fuel lines with clear ones. What size did you use, just out of curiosity?

He said 1/4", I believe.  I'm probably going to use this:

http://www.amazon.com/Motion-Pro-Tygon-Ultra-Fuel/dp/B0022ZWTA0/ref=sr_1_6?s=automotive&ie=UTF8&qid=1329459234&sr=1-6

I'll shop around and try and get it cheaper though.

Quote from: shonole on February 16, 2012, 11:14:27 PM

Quote from: Kijona on February 16, 2012, 11:09:16 PM
I've been considering replacing my fuel lines with clear ones. What size did you use, just out of curiosity?

He said 1/4", I believe.  I'm probably going to use this:

http://www.amazon.com/Motion-Pro-Tygon-Ultra-Fuel/dp/B0022ZWTA0/ref=sr_1_6?s=automotive&ie=UTF8&qid=1329459234&sr=1-6

I'll shop around and try and get it cheaper though.

...oops.

Did you just plug up the vacuum from the carb with some hose and a bolt? I am looking to do this to mine as well with two small inline petcocks to keep the reserve functionality. We will see how it goes.

I am always amazed at the lengths people go to in order to fix something that doesn't need fixing.
What is it with the fuel petcock? Bikes have either a vacuum petcock or a fuel pump. What's the big deal if one goes bad? Few of us ever have a petcock problem but those that do seem to proclaim it to the work as the evil work of the devil and must be replaced.

What about all the other parts that wear out?
Fork seals? Don't replace them - weld the fork tubes.
Tires? Need air? Peshosh! Fill the tires with solid rubber so you don't need to put air in.
Oil filter dirty? Just remove it!
Brake pads? Clutch plates? What other parts wear out and you decide to scrap the original design and cobble up something else?

Have you thought of this? So your petcock is going bad. Just put it in PRIME. That bypasses the vacuum and now acts like an on/off valve. No need to replace it with anon/off valve. Use PRIME.

Why would you want to return to the old days of having to remember to turn the fuel on and off?

Vacuum petcocks are reliable and are in millions of bikes. If they didn't work they would have stopped using them.

So jump down from the "Petcock is Evil"soap box. realize that they can go bad like any other part. No reason at all to cobble up a hack job to replace it. Just get another one and you're good for another 15 years or more.

There have been 2 reasons people at the Bike Cave thought they had a defective petcock.
One: out of gas!
Two: Vacuum line was not connected.
And the third possibility: the wrong in-line fuel filter was installed and slowed the fuel flow.

Haven't really had a bad petcock. Only THINKING it was bad due to #1 and #2 above. (I have heard of #3.)

Now back to reality. Petcocks work. Like any part, one can go bad. Replace it if it went bad - like you would replace any other part on your bike that went bad.

If you want to be stubborn, at least leave it there and switch to PRIME to run. Same difference as a plain petcock with ON and OFF. Plus you don't have to do any work for an ON/OFF system: remember about PRIME.

Never had a petcock issue. Thought I had one on an old 82 GS, but it was CDI box.

Vacuum petcocks work well. People swear by Pingel, et al except when they forget to ALWAYS turn off the gas only to find their garage floor full of gas in the morning. GS Twins have weak float needle seats. Then you must remember to turn on. Nothing like being in the middle of an intersrction and out of gas in float bowls.

Turn off gas every time and you are ok. I mean every time.

My '96 is probably sporting the same hoses it had when new, so my fuel starvation problem at 70 mph is most likely due to vacuum leak.  First, I plan to renew the fuel and vacuum lines.  The, the next time I ride at that speed, if I have an issue, I will switch to Prime and see what happens.  Makes sense, no?

@ adidasguy Like hell I am going to spend $50 for a used petcock when I can rig up something for half the price that will work better and last twice as long. I don't really mind turning one more knob as I get off the bike. And yes, if I thought I could cobble together a clutch plate that worked better and was cheaper than buying a new one I would.

Sorry - a little testy aren't we?

You're free to do whatever you want. Its your bike. I was expressing my opinion.

By the way, new ones are $50. Used ones are $19.95.

I deleted my petcock - if my bike ever fails on me, at least I won't be troubleshooting vacuum petcock syndrome on the shoulder of I - 95 or somewhere.