Had what sounds like the standard petcock caused fuel starvation problems today.  Took the petcock off the bike, cleaned it (not much crud or other such crap in the thing) and reinstalled.  Found what I had suspected from when I first got into the carbs over a month ago; the petcock only works in the "On" position with engine vacuum pulling the diaphram up and off the stop.  Otherwise the thing doesn't allow fuel to flow through the thing. 

So what's up?  Because of the way the thing goes together, I don't see how the petcock could be put together wrong.  Is there a chance of this and I'm just inept?  Or is there something else going on?  I'm really wishing there was a drop-on replacement for these petcocks, or one that with a simple mod would fit in place of what sounds like a not very good item from Suzuki.

I may not be completely understanding what you are asking, but you are describing is exactly how the petcock should function - allow the fuel to flow only when the engine is spinning.

Yeah that is excatly the point, when the engine is off the petcock turns off so that the carbs do not overfill with gas.

Whent the engine fires up and starts to pull vacuum(taken from the left carb) then it opens allowing fuel to flow

However, in PRI there should be no vacuum required to allow fuel to flow. THis is used when you have just serviced the carbs and need to  fill them with out having to crank the bike over and over until they fill

Here's a better explanation of what's going on.  I've got an automotive filter in there for fuel clean up duties.  It's between the petcock and the carb inlet.  I used that because I figured the bike could use what I assumed to be better filtration vs. what bike filters would offer.  I got left on the shoulder 3 times today by this bike, I'm not sure why this started now.  But in every instance, the clear auto fuel filter was empty.  After a while of waiting, cranking the bike would give vacuum to the petcock and it'd open up and I'd get fuel in.  I pulled the petcock apart, thinking crap had built up (since nothing else seems to have changed, what else could it have been?) and the thing was pretty clean inside.

Put it back together with a new filter.  I take off on the thing and head off on an interstate-style highway.  70 mph.  After a while, whee, I can tell the thing is starting to miss out and fart, etc.  Pull over and again, the damned filter is empty.  Switch to Prime and still no fuel comes into the filter.  I'm now on the shoulder and I've got the factory tool kit and some dayliight.  I start to think about trying to run a hose from the tank to the filter, I still assumed the petcock was to blame for all of this.  Pulling the hose off of the filter inlet from the petcock, I have a *lot* of nice fuel flow with the petcock on Prime.  A lot more than I should have assuming the petcock is crap.  I plug the thing back together, and leaving it on Prime, I'm seeing more flow than when I was first pulling over to the shoulder. 

I was able to run the thing home by taking a state highway where I didn't have to do over 60 mph. 

My plan from here is to pull out the automotive style filter and run without.  This may see me pulling the float bowls off the thing a couple times a year to clean out crud but I shouldn't be parking on the side of highways anymore for this issue.  Should be a good time.

I actually use an automotive filter myself, but not clear. I went to an automotive place and, making sure that nobody saw me, opened the package of every non-paper filter they had and blew with my mouth through it.
Picked the one with the least resistance, which actually happened to have even lesser resistance than the cheapo clear motorcycle filter I had at home. From now on I know the filter model I need and will simply buy those at the autostore as needed.

When you try to look for problems in your existing petcock, don't forget to look inside of the vacuum spigot.
Here is all the crud I pulled out from mine, which clearely would diminish the amount of vacuum pull on teh diaphragm and restrict fuel flow - http://culbertfamily.com/jenya/gs500/petck_dirty.jpg

As far as getting stranded on the shoulder, that happened to me only twice before I got convinced that I cannot ride like that any longer and modified my petcock from being an auto shut off to manual.
All described in http://gstwins.com/gsboard/index.php?topic=19363.0

I had never since experienced even a slight sign of fuel hesitation. And I usually go on average 85mph when commuting.

Yeah, I think that petcock is going to get the business tomorrow.  I've already got JB Weld, real vacuum caps, and some free time to do this. 

Want to share with the group what kind of filters you're using?  My tank isn't remotely perfect and rust free, the old filter I pulled off had some flecks of crud at the bottom.  I used a Purolator brand filter to replace it with.  I wish there was a way to route the thing so it'd have some drop to it to get into the fuel bowls, instead it's kind of the low point of that hose coming from the petcock.  Seems like fuel has to somewhat climb back up to get into the carbs, and that doesn't sound like an ideal situation. 

I thought you may ask me for the filter model. And I would have gladly told you if I remembered.
Need to take the fuel tank to see. Hmm, 10:30pm. Oh well, will go do that. Be right back.

Jenya

Okay, some of the lettering rubbed off. I am not sure on the last digit or even if there is the last digit.
But I read FRAM G351(and may be 7). If you will end up getting it, could you please confirm the number.

-------------------------CORRECTION--------------------------

It is FRAM G3515 for sure.
As seen here http://www.rockauto.com/ref/Honeywell/FRAMDetail.html?Style%20194.jpg

Oh and as far as the drop of the hose goes, it all doesn't matter. All that matters is the difference in heigh between fuel level in your gas tank and the point where the fuel enters carburators. You can zig-zag all you want in between, it won't matter.

Jenya

Good point about the drop, although seeing a mostly empty fuel filter will start to rattle the mind, you know? 

I used a little filter that I got at the bike shop. It's clear and plastic with a sintered metal filter ellement. I wouldn't recomend the sintered metal since I found some fine crap in my carbs that made it's way through the filter. It looks just like this one

http://www.jcwhitney.com/autoparts/Product/Pr-p_Product.CATENTRY_ID:2002783/c-10111/Nty-1/p-2002783/Ntx-mode+matchallpartial/N-10111/tf-Browse/s-10101/Ntk-AllTextSearchGroup?Ntt=filter&reviewflag=1#review

Also, I think it may not allow fenough flow on long hills, high RPM, full throttle stints. But the mike might be that slow anyways so I'm not sure.
I think the paper ellements are better at catching the small stuff and I like clear filters so You can see if there is any crud or air in it.

I was thinking about getting one of these if I ever order something from JC Whitney. It's pretty compact but suposedly "high flow" and it's paper and clear plastic. Haven't used it but it looks good.

http://www.jcwhitney.com/autoparts/Product/Pr-p_Product.CATENTRY_ID:2002784/c-10111/Nty-1/p-2002784/Ntx-mode+matchallpartial/N-10111/tf-Browse/s-10101/Ntk-AllTextSearchGroup?Ntt=filter

G3515 seems to be doing a great job at filtering. I have been using it for nearly the whole Summer of 5 days a week riding, and recently, while rejetting, I haven't found any trace of a dirt getting into the carbs. All is prestine clean just as it was right after I cleaned the carbs and added this filter.

Even though I would love to have a clear filter, I don't know if most motorcycle filters would do as good of a job as this automotive one. It, being larger, provides better throughput while, hopefuly, not compromising on filtering capacity. That is just the name of the game, if you are to make a filter that filters well while still allowing a high flow, you'll need lots of the filtering area.

I may pick up another G3515 tomorrow and open up the one I have to see how it is constucted and its condition.

Jenya

T7

What Wrecent_Wryder said. 

Cellulose filters designed for pressurized systems don't allow fuel to flow enough for our non-pressurized system.  It just trickles out, so you'll get fuel starvation.  I know firsthand.

I've stuck with clear filters for this very reason, being able to see just how much fuel is in that last leg of the system before entering the carbs.  The filter was indeed empty.  What caused me to change from the filter that had been working for a month to the new Purolator (the old brand of filter is unknown, it was packaged in the Help stuff on a rack at O'reilly's) is that I was left on the shoulder twice by the thing earlier in the day.  There was crud in the filter, but less than a teaspoon's worth. 

I don't really think it's petcock either, as I'd throw the lever over to prime and fuel wouldn't enter the filter.  Wondering if heat is causing the filter to internally pressurize enough so that fuel won't enter the thing reliably.  Which sounds odd though, since I can do under 60 mph or under 6k RPM for over half an hour and be fine, but elevate things to 75 and it all starts going south on me.  The reason I originally suspected the petcock was how the thing wouldn't dump in any fuel, even when going over to prime (this was with the filter in place mind you) until I threw the petcock lever back up to On and started the engine.  At that point, bang, I have a bunch of nice flow into the filter while the engine is running.  This may support my pressurization idea of the filter, that the carbs are pulling on the vapor pocket in the filter and breaking that up enough to allow fuel in.

I also know that the filter doesn't need to be full, it should be 1/2 full or maybe a bit more.  What I was seeing was an empty filter, and commented on that mostly as a joke, sorry that I wasn't clear on that.  Going to try to get ahold of a clear Wix fuel filter for the thing, I always had good luck with that brand.