BS32SS needle and seat leak driving my nuts

[jplombardich]

Hey folks,

I have been working on my 1981 GS750X and recently removed the tank. In order to fire up the bike, I have been using a clear hose and funnel for the gas kind of gas tank height. The bike runs great but when I turned it off, I noticed that gas was slowly going into the carbs with the engine off.
I did a number of tests with liquid and air as I have a cabr pressure tester, and I found needles and seats were not in great shape so bought a re-build kit on Amazon. I assembled all back with the new parts and tested the carbs with the clear hose and funnel again, and then with air using the carb pressure tester. There was an improvement, but there is still a minor leak through each needle that is driving my nuts (even pressing the floats and pushing the needles)!!! Seats' orings are sealing perfectly.

I did a bench test leaving the carbs overnight with the clear hose full of gas (~10inches) and the carbs kind of covered with paper towels, the day after the gas level was a couple of inches down but I was not able to see any gas anywhere, hahahaha

The other bench test I did on the new parts was to pressure test the system with air and spray water+detergent on the needles. Then I found that it can not hold pressure as it leaks through each needle.

The questions are, would a small leak through needles be normal? or the expectation is to have a 100% leak-free system? or do you guys close gas tank valves every time you park/stop the bike?

 

[Nessism]

All GS's use a fuel valve that shuts off fuel flow when the engine stops, unless the valve is set to the "prime" position.

 

[jplombardich]

Thanks Nessism, does it mean I don't have to worry about needles not selling perfectly? Does it automatically shut off fuel flow?

 

[Nessism]

The float needles must seal relatively well in order for the bike to run properly. They don't need to seal perfectly, such that you can leave the fuel petcock to the prime position even when parking the bike.

Follow the factory Suzuki method of checking the fuel level with a clear tube. It's easy to make your own tool to do so. Then verify the proper fuel level in each carb. The fuel level should remain steady when doing this test for a good 5 minutes or so. Beyond that, if the level creeps up, it won't affect riding.

Oh, and make sure your petcock stops the flow of fuel when the bike is turned off. When the petcock fails sometimes it sticks on and fuel flows all the time.

 

[rphillips]

Exactly, fuel valve is opened by vacuum, when bike is running, shuts off when vacuum is gone (eng. off). Pre appx. 1975 everyone needed to remember to turn the fuel valve off after riding, just cause of the problem you're seeing. Since then most all bikes have some type of auto fuel shut off. As long as your bike's fuel valve is working properly, you'll never know the needle & seat is leaking lest it starts leaking fuel faster than your bike is using it, you should be good to go

 

[jplombardich]

Thanks Nessism and rphillips,
I checked fluel level but just for a second to make sure it is right, will check it again and monitor it for a couple of minutes.
Comments about petcock are great and it is true, in this case, needles and seats were probably leaking forever until I realize it when I did the bench pressure tests without the gas tank and engine off.
Thank you folks!

 

[jplombardich]

Bench test was a success! Float leves were stable for 2 hours and needle and seats are working fine.
However, fuel petcock vacuum diaphragm spring is missing and the weird thin washer broken. Is it reparable? I noticed a kind or rivet or pin on the other side of the oring. Any suggestion where can I get a kit for it?

 

[salty_monk]

It would be very unusual for a rebuilt petcock to hold fuel back..... Many have tried and many have failed (including me...). Usually internal corrosion creates a problem even if the seals are good. I would go for a new one.

 

[Gorminrider]

Yes they are hard to fix for no known reason. I'm at 50%. Weirdly, swapping parts from ORIGINAL taps can work where New Kits do not.

fuel petcock vacuum diaphragm spring is missing

I've never seen a kit that includes the spring.