2004 Petcock question

[benntn]

When the tank is off and the shut off valve is on, should gas come out of both tubes?

My bike will not run unless it's on PRI then stalls.  The vacuum line to the frame petcock is connected on both ends.  I've clean the carbs twice.  I have new fuel lines from the tank to the frame petcock.  I removed the tank petcock and cleaned and blew it out as well.   

[adidasguy]

It will come from both tubes if you have enough gas in the tank.
It will come from one tube if low on gas.
It will come from no tubes if out of gas.

[Manaenrc]

The vacuum setup on the secondary petcock is prone to issues. I had major starvation problems with mine as well.I ended up swapping out the stock petcock for one that does not use the vacuum setup. This made a huge difference in fuel flow.

Start by making sure the vacuum line is still attached to the carb and the petcock.




Sent from my SPH-D710 using Tapatalk

[benntn]

Thanks.  It only has about a gallon of fresh gas in it now since I started this job.  When I first removed the tank it had about 3 or 4 gallons of old gas in it and I recalled that it wouldn't drain from the one of the tubes then as well.  The vacumm line is connected.  I've drain the thing about three times now since it just a pain to remove and put back, so I'm just lost as to why this thing will not run.

[adidasguy]

Be sure tank petcock is straight down ON. One gal = you're on reserve so fuel only from one tube.
If bike has sat for a while (implied by mention of old gas) the vacuum petcock might be stuck.
With a clean tube, connect to the output of it.
Put in PRIME. BLOW! Air will go through.
Now try on ON and RES. Air will go through one inlet at a time. If not, BLOW HARDER! The diaphragm might be stuck. A good blow job can get things free and un-stuck. If not, then change the petcock. Easy to get and THEY DO WORK. (Note: As you do it, it may honk like a new year's party horn. That's OK. The diaphragm is vibrating as air goes past. There's no vacuum pulling it open.)

Above is how I test petcocks to be sure they work. also how I un-stick one sitting in the drawer for a while. I NEVER have problems with the vacuum petcocks on 4 GS500's with one as old as 1992 original petcock. Sometimes I blow gently and use a turkey baster or syringe with a hose to the vacuum line to get come vacuum to open the valve.

So many of us never have a problem. Those with problems often have an old one or fuel hoses routed so they are pinched or a vacuum hose problem. When they replace with something else, BAZINGA! No problem because fuel hoses are routed differently and are no longer partially pinched.

[benntn]

Be sure tank petcock is straight down ON. One gal = you're on reserve so fuel only from one tube.
If bike has sat for a while (implied by mention of old gas) the vacuum petcock might be stuck.
With a clean tube, connect to the output of it.
Put in PRIME. BLOW! Air will go through.
Now try on ON and RES. Air will go through one inlet at a time. If not, BLOW HARDER! The diaphragm might be stuck. A good blow job can get things free and un-stuck. If not, then change the petcock. Easy to get and THEY DO WORK. (Note: As you do it, it may honk like a new year's party horn. That's OK. The diaphragm is vibrating as air goes past. There's no vacuum pulling it open.)

Above is how I test petcocks to be sure they work. also how I un-stick one sitting in the drawer for a while. I NEVER have problems with the vacuum petcocks on 4 GS500's with one as old as 1992 original petcock. Sometimes I blow gently and use a turkey baster or syringe with a hose to the vacuum line to get come vacuum to open the valve.

So many of us never have a problem. Those with problems often have an old one or fuel hoses routed so they are pinched or a vacuum hose problem. When they replace with something else, BAZINGA! No problem because fuel hoses are routed differently and are no longer partially pinched.

Thanks Adidas,

Ok I'll give a BJ when i get home after work and see.  LOL

If i buy a new one, what and where would I get it.  The OEM one is over $100, ouch.

[adidasguy]

Parts whores on the board have things like that.

[Manaenrc]

I find it curious that they don't sell a diaphragm rebuild kit for these pet cocks. I know that's all I would have needed to get mine working properly. But when you go to suzuki all they want to sell is the entire petcock. With this ethanol the rubber diaphragm is going to get hard and stop functioning properly.

Oh well things that make you go hmmmm...

doesn't matter I replaced mine with a much better solution.

[benntn]

Be sure tank petcock is straight down ON. One gal = you're on reserve so fuel only from one tube.
If bike has sat for a while (implied by mention of old gas) the vacuum petcock might be stuck.
With a clean tube, connect to the output of it.
Put in PRIME. BLOW! Air will go through.
Now try on ON and RES. Air will go through one inlet at a time. If not, BLOW HARDER! The diaphragm might be stuck. A good blow job can get things free and un-stuck. If not, then change the petcock. Easy to get and THEY DO WORK. (Note: As you do it, it may honk like a new year's party horn. That's OK. The diaphragm is vibrating as air goes past. There's no vacuum pulling it open.)

Above is how I test petcocks to be sure they work. also how I un-stick one sitting in the drawer for a while. I NEVER have problems with the vacuum petcocks on 4 GS500's with one as old as 1992 original petcock. Sometimes I blow gently and use a turkey baster or syringe with a hose to the vacuum line to get come vacuum to open the valve.

So many of us never have a problem. Those with problems often have an old one or fuel hoses routed so they are pinched or a vacuum hose problem. When they replace with something else, BAZINGA! No problem because fuel hoses are routed differently and are no longer partially pinched.

Thanks Adidas,

Ok I'll give a BJ when i get home after work and see.  LOL

If i buy a new one, what and where would I get it.  The OEM one is over $100, ouch.

Ok I did as u suggested and it still will not run very long.  It will only start if I've primed it and even then I'm having to give it throttle and the it will eventually die and not start again.  I've double check the vacuum hose and there are no kinks.  I also check the float hight and it appears to be good.

If the petcock diaphragm is sticking after I blew though it (I heard the horn too), shoudn't it run normally until the fuel ran from the line?

[Manaenrc]

yeah would idle for a while and then die, starving for fuel.

Sent from my SPH-D710 using Tapatalk

[Funderb]

If the petcock diaphragm is sticking after I blew though it (I heard the horn too), shoudn't it run normally until the fuel ran from the line

it will run for a bit, until fuel pressure is too low and the bowls don't fill up. you need a tank with sufficient fuel inside to provide fuel pressure to the carbs. theres no fuel pump to help ya out.

[benntn]

If the petcock diaphragm is sticking after I blew though it (I heard the horn too), shoudn't it run normally until the fuel ran from the line

it will run for a bit, until fuel pressure is too low and the bowls don't fill up. you need a tank with sufficient fuel inside to provide fuel pressure to the carbs. theres no fuel pump to help ya out.

I did add another gallon of fuel and it still doesn't run very long.  I've ran the battery down trying to figure this out.  So now it's on charge.

Can I bypass the frame petcock just to test to see if it bad?

[adidasguy]

Sounds like petcock is OK.
You can bypass it. Slup a connector between the hoses for the tank and going t the carbs.
a "T" would be nice - connect both tank line to it then on to the carbs.

Here's an idea: there was old gas in it for a long time? Could the in-tank fuel screen on the tank fuel valve be gummed up? Does fuel flow freely from the tank? You can try for a short while with the in-tank screen removed. There would be no reserve or filter but would tell you if that screen is the problem.

[benntn]

Sounds like petcock is OK.
You can bypass it. Slup a connector between the hoses for the tank and going t the carbs.
a "T" would be nice - connect both tank line to it then on to the carbs.

Here's an idea: there was old gas in it for a long time? Could the in-tank fuel screen on the tank fuel valve be gummed up? Does fuel flow freely from the tank? You can try for a short while with the in-tank screen removed. There would be no reserve or filter but would tell you if that screen is the problem.

Ok, I'm going try bypassing it when it home.

I did removed the tank fuel valve and cleaned it.  I even peeped threw the hole and saw daylight and blew air through it.

Also I'm now confused as to what hose goes where.  I did mark them before removing but I've changed fuel lines twice since then (don't ask).  I tried swapping them and I get the same results.  The "how to" here shows the res on the short tube and the "on" on the long tube but I saw a different chart on here that show 3 different makes together, where they were swapped on the 04 and up.  What's right?

When I had drain the tank when it was off the bike and the valve on, most of gas came out of the long tube which to me means it should be connected to the "on" port on the frame petcock, right?

[Manaenrc]

The reserve is on the longer rear tube on the tank (main being the other front connection). On the petcock under the connection toward the rear of the bike is the reserve, the front is the main.

[benntn]

Good news, I think.  I bypassed the petcock and she runs!!!

Now, what to do?  Should I replace it with the recommend Honda one, rebuild this one, or buy a new OEM one?  I tore down mine and it looks ok.  Maybe a vacuum problem?  How can I test the vacuum?  All the lines look good.  If I start it again and put my finger over the vacuum hose to the petcock should I feel a lot of suckion?

[adidasguy]

.....buy a good, used one from a parts whore? 

I do not think you will feel much suction. However, it should be enough to pick up a small square of paper. If it can't do that, you're lacking vacuum.

Now that you know where that line runs and branches off, pinch off all the other places it goes and see if there is more vacuum. If there is, check the other 2 places that line goes. One might be leaking.

another test is apply vacuum to the petcock manually. Run the fuel out to a cup with a short hose. If you apply vacuum and fuel flows freely, go back and check for a vacuum leak. You can apply a vacuum by sucking gently on a piece of hose. You can use the suction of a turkey baster or syringe. It shouldn't take much sucking. There isn't much of vacuum required.

[benntn]

.....buy a good, used one from a parts whore? 

I do not think you will feel much suction. However, it should be enough to pick up a small square of paper. If it can't do that, you're lacking vacuum.

Now that you know where that line runs and branches off, pinch off all the other places it goes and see if there is more vacuum. If there is, check the other 2 places that line goes. One might be leaking.

another test is apply vacuum to the petcock manually. Run the fuel out to a cup with a short hose. If you apply vacuum and fuel flows freely, go back and check for a vacuum leak. You can apply a vacuum by sucking gently on a piece of hose. You can use the suction of a turkey baster or syringe. It shouldn't take much sucking. There isn't much of vacuum required.

Thanks Adidas,

Ok I'll try that tomorrow.  I feel much better now that she ran. 

[benntn]

Well I finally got a new frame mounted petcock and installed it last night.  Guess what, same problem as before.  Grrr I'm about to shoot this bike.     I guess I'll remove the valve from the tank and check it again but I just don't understand why I can't figure this out. 

[jestercinti]

Well I finally got a new frame mounted petcock and installed it last night.  Guess what, same problem as before.  Grrr I'm about to shoot this bike.     I guess I'll remove the valve from the tank and check it again but I just don't understand why I can't figure this out.

Sorry if any of this is redundant, but here's how I'd tackle this: 

1. You mentioned that you bypassed the petcock.  I am assuming it's the frame mounted one with the dial (I believe the tank outlet is also called a petcock).  Try bypassing again going directly from the tank using the outlets 1 at a time directly to the carb to test.  Cap the other tank outlet off naturally using vacuum caps available from Autozone.  This will tell you if the tank petcock is good in both ON and RES.  Go for a longer ride close to your home/shop to confirm that each outlet is working as expected.  If all is well on both sides, then it's got to be either a kink somewhere in one of the hoses when it's all put together or the frame mounted petcock is having issues.

2.  If the problem persists going directly from the tank to the carb, AND you have ruled out the tank petcock screen, check ignition system.  Had your symptoms once on an 82 GS450 (older version of the GS500), and it was a CDI ignition box with an intermittent problem.  Everything pointed to fuel starvation.  Spent a lot of time and money on a new petcock, new fuel hoses, carb cleans, etc.  Didn't realize it was ignition related until one cylinder quit firing all together when the CDI abruptly failed.

EDIT:  I searched, and looks like in the unlikely event it is the CDI Ignition Box, you will need a special tool to test.