GT500 Petcock Leak

[speedfreak]

I have a weird issue. The petcock on my 77 gt500 project leaks after running for about 5 minutes. I have tracked it down to the small hole in the body which somehow connects to the diaphragm. It just starts spitting out from there.

1 - what is the purpose of the hole. I would assume allowing air behind the diaphragm to allow it to open and close without a build up of pressure. Please correct me...

2 - can it be plugged. Without tearing off the petcock and trying to muck with the diaphragm, I don't know how else to stop the leak....

Help!

[alanr]

the diaphragm is the problem,I had the same trouble.if you take off the fuel lines and it drips from the petcock new diaphragm needed.I have had this problem with both T,s.and have both diaphragms replaced. http://www.trademe.co.nz/Browse/Listing ... =774589073" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;. this is what I used.probably no good for overseas.

[yeadon_m]

You have a pin holding the diaphragm. It should remain dry on the small air vent side. Remove it and see if you can patch it with a drop of fuel resistant adhesive. I succeeded with a GT750B tap that failed with identical symptoms. Good luck!
Mike

[speedfreak]

So is the idea of that hole to ensure there is no air pressure on the back side that holds it open? What is the result of sealing it? I'm happy to try, but just want to get and idea of exactly what I should be watching for afterwards... Constant leak or fuel starvation? (Although I suppose it will be obvious enough once running - I just like to understand what I'm doing when I do it...)

[Coyote]

Constant leak or fuel starvation?

Probably both. The hole has to be there for the diaphragm to operate. As stated there should be no fuel on that side. The only way for fuel to get on that side is through a hole or tear in the diaphragm. You need to disassemble and patch that tear or hole or replace the diaphragm. You won't get there any other way. Since it takes about 5 minutes to start leaking, I would suspect a real tiny hole in the diaphragm. The only other option is to trash the petcock and replace it with a manual unit. Lot's of guys go that route yo get away from the problematic vacuum operated type. It was a great idea but Suzuki dropped the ball by not making any user replaceable parts. Namely the diaphragm and o-ring,

[speedfreak]

Alright - thanks. I guess I'll pull it back off and try to repair it. Hopefully I can because I am quickly running out of funding and patience (in that order). Thanks for the help.

I'm sure I could find it by searching, but is there a preferred replacement petcock for the GT500 that comes at a reasonable price? Not that I want to cheap out, but I'm not building a show bike...

[titan performance]

Many years ago, while touring through Europe, the diaphragm in the petcock of my T500 failed. We were in Northern Italy, and each time we stopped, my wife said her foot was getting wet. The weather was very hot, and the fuel that was dripping from the pin hole in the tap was evaporating as soon as it hit her ankle, so there was absolutely no sign of any moisture when we looked. I told her she was mad, and we carried on each time.....when we finally pulled up for the day, I saw the drip from the tap and realised what was happening. With no chance of obtaining parts to repair, I used glue to plug the hole, and we continued our tour with no ill effect. In fact, that tap stayed on until quite recently. Obviously the fuel flow will not be stopped by the tap with no vacuum, but as long as your floats and valves are set correctly, flow should still stop....mine did.

[Coyote]

You lost me on that one. The plunger in the center of the diaphragm that carries the 'shut off' o-ring is spring loaded from behind and stays shut till there is a vacuum. The vacuum overcomes the spring tension, pulls the o-ring back and allows fuel to flow. No vacuum - no flow. If what you are saying actually worked, the o-ring had to be already shot and not doing it's job to begin with.

[speedfreak]

So I pulled the petcock apart tonight and found that the area of the diaphragm right at the base of the "piston" was severely dried out. There must be one or more cracks. I've sealed it up with gasoline resistant silcone. Letting it dry overnight and reassemble soon. Will test once I get my new tympanium and check valves and get everything put together.

[speedfreak]

So after fixing my other problems, and repalcing the diaphragm with (what I thought) was a good used one, I still have the leak. Look slike even the used rubber was cracked. So, next question, I've been following the latest thread on a manual petcock, but is there a unit that bolts on with no mods required?

[speedfreak]

And can someone comfirm that the OEM part number for the petcock is "44300-33600"? Want to be sure I have the right #...