Petcock advice

[Erika]

Hi,

I went to reserve on a trip, and now I have trouble with the On position... I'm not sure why. When the petcock is in the On position, my bike stalls and dies while on the highway, which is dangerous. I know it has something to do with the petcock, maybe crud got in from reserve, or maybe the diaphragm is old and cracked. I want to make sure I can find or repair the diaphragm before I tear it apart to clean it. I've been reading the threads for rebuilding the vacuum operated petcock, and am learning that nobody supplies the gaskets and diaphragm. My question is: Is there a work-around? I've been running it in Prime and it seems to be ok. If the diaphragm gets worse, will the petcock stop working in prime? My thought is that I could continue to use it like a regular "On/Off" petcock if I can't replace any parts. Any advice?

Thanks,
Erika

[jdoorn14]

I understand there is no true repair kit for the petcock. Once the diaphragm is dried/brittle/broken, you must replace. Not sure I'd trust the petcock not to leak gas into the vacuum lines if the diaphragm continues to get worse, but that's just me.

You could probably have some luck finding a decent used petcock on ebay from one of the wreckers, though new for my '07 is only about $85 + shipping from partspitstop.com. That's the online retail wing of one of my local dealerships. They usually have better prices than Ron Ayers or others from my experience.

[afatrat]

If you're sure your carbs are clean and fuel hoses are good, I would just replace it. (not sure what year your bike is but, http://www.ebay.com/itm/NEW-89-00-SUZUKI-GS500-GS500E-PETCOCK-SECONDARY-/201565055015?_trksid=p2141725.m3641.l6368) I had the same problem where I had to use prime on the highway. I tried cleaning the petcock and gas cap but couldn't seem to alleviate the problem so i replaced it. I haven't been on any highway runs longer than 30 minutes since replacing it but so far so good.

[lucas]

If the petcock works in Reserve you should use that instead of Prime to lower your chances of flooding your engine/airbox with fuel overnight.

Don't know what is causing the problem you are having.  You could test it out yourself and clean it if there is gunk in there.  Here is how I'd do it. 

Close the valve under the tank, label the fuel lines at the frame petcock to make life a little easier when reassembling.  Remove the frame petcock and disconnect the hoses.  Dry it off a bit and blow into the On and Reserve ports and feel if there is resistance or blockage, switching the valve to all three positions.  The taste of fuel isn't too terrible in small doses.  You can avoid the taste of fuel if you want to try blowing compressed air or WD-40 thru.

Then on the vacuum port, the tiny one at an angle, apply suction and you should be able to feel the diaphragm click open.  The vacuum port won't taste as bad as the On & Reserve.  Checking the diaphragm might not be necessary if your bike runs while on Reserve because that would indicate a working diaphragm.

[Bluesmudge]

I believe PRIME draws from the reserve line, so there is also a possibility the tank petcock or ON fuel line has a blockage. You can pull the ON line off the frame petcock and make sure that fuel pours out all over you.

[Erika]

Yeah, it's a bummer to buy a whole new part only to have the rubber bits slowly destroyed by ethanol. I'll have to investigate to see what's dirty and what isn't. I wonder if I can block the vacuum part off completely so I don't have to worry about it anymore. Bluesmudge, I didn't know Prime pulled from the reserve line. I'll have to test that, which could be exotic, as long as nobody lights a match.

[Watcher]

If you don't find any line blockages and come to the conclusion that it IS the petcock that went bad, you could always get a standard on/off ball-valve and plug the vacuum coming off the carbs.

Simple way is straight off the reserve line, through the ball valve, into the carbs, but then you effectively lose your "reserve".
If you want to keep a reserve, there's a way to do it with a T-fitting and a second ball valve.  I drew a little diagram:

[lucas]

Adorbs

[ShowBizWolf]

+1 

[crazydred]

Just got a GS500 used 99 model, 12000km

My petcock set to ON also stalls the bike..

I've taken it apart and the diafragm is in good shape, I cleaned and blew it anyway.
I've drain the gas tank, while draining the gas only came from the reserve line.
I've checked the gas tank filter, it was not dirty (cleaned it anyway), I shot air into the ON and RES lines and it came right out through the gas filter.

Carb vaccum line is attached to petcock.

No idea why it does not work..

[jdoorn14]

Crazydred, you may have a kinked ON gas line or a clog in that line/attachment to the petcock, assuming that using the reserve setting on the petcock works and doesn't stall the bike.

Out of curiosity, when is the last time the fuel lines were swapped on your bike? IIRC recommended maintenance says they should be replaced every 4 years. If the bike has been sitting for any length of time with ethanol in the fuel lines you might have some sludge clogging the works.

[crazydred]

The fuel lines are brand new.

When draining the tank gas only came out from the reserve line..

[jdoorn14]

So you had both gas lines off the petcock and draining into a gas can and gas only flowed from the reserve line? How much gas did you drain from the tank?

[crazydred]

Yes that's what I did.
I drained the entire tank so I could check the gas filter

[jdoorn14]

If both gas lines were dangling from the tank freely into your gas can, then I'd suspect either you've still got a blockage/gunk/kink in the ON fuel hose, or else somewhere in the tank filter. Once the frame petcock is out of the equation, both lines should drain equally until the volume is low enough to only drain through the RES line.

[afatrat]

The fuel lines are brand new.

When draining the tank gas only came out from the reserve line..

You do have more than a gallon in the tank, right?

[jdoorn14]

He said he drained the full tank.

I made an assumption that the "full tank" was full, but definitely worth asking at this point.

[crazydred]

Well, I got at least 5 liter of Gas  out of it.
But I will try again because the tank was not full and it was leaning.

[jdoorn14]

5 liters is approximately 1.3 gallons to those of us who don't measure gas in metric units. With the 4.5 gallon tank on the 1999 GS500, you may well have not had enough gas in the tank to quite hit the part of the tank petcock the ON line uses. In this case, it would be quite normal to expect that all the gas would drain through the RES line.

[crazydred]

I understand that could be the issueissue,  I will top the tank next time and try again.
Gas should flow from both lines untill it reaches the reserve level right ?