Slow gas/drip leak from carb

[20ftollie]

Just picked up a great '75 XS650B with only 2,500 original miles.... a true barn find. Sat in a Detroit garage for over 25 years before my uncle grabbed it up a couple months ago. It's since been gone through - new battery, carbs & petcocks cleaned, tank dipped, plugs, etc.

It runs really well and a lot of fun to ride. I'll admit that I'm not very experienced working on old carbs but I love old bikes and am willing to learn (I've been studying the carb guide).

So the issue I'm having is that when the bike sits, there is a very slow gas drip coming out of the drain tube underneath the right side carb. It's very slow but enough that there was a good size puddle under the bike the day after it started happening. It only leaks when the bike is off. While it's running, there's no problems. The petcocks are turned off while it's leaking.

So is the petcock itself causing the carb to overflow? When I pull the gas line off the petcock, no gas comes out while it's turned to off.

Or is the float level adjustment wrong, causing the gas to keep coming out? If so, is it possible to remove the bottom of the carb to adjust the float without pulling the carbs off the bike?

Any help is appreciated.

-Matt

 

[5twins]

The float needle is probably not sealing completely in the offending carb. As it sits over night, the fuel left in both lines drains into that carb and overfills it. A slow leak like this wouldn't show while running. The bike uses the fuel faster than it can overfill. Yes, you can access it with the carbs in place. Drop the float bowl, remove the float & float needle, and remove the float needle seat. It might just need a cleaning or it could be worn and need replacing.

 

[Tomterrific]

Along with 5t comments I'll also suggest the float itself might have a small leak. When running, the float warms and the liquid inside is forced out plus the bike is using fuel fast enough. As the engine cools liquid is sucked back in the float sinking it and raising the float level.

It's probably the needle and seat as 5t mentioned above. You seem as lasy as myself so what I would do in your circumstance is to drain the float bowl, then open the petcock and run fuel through the needle and seat. Hopefully this will wash out a speck of dirt that is holding open the valve. Drain all the fuel through a clean paper towel and see if any debris come out. Capture the gas and reuse it, Max. :^) This step takes no time at all and on the off chance it fixes the problem you can do something important with your time, like flush the brakes system again.

Tom Graham

 

[grizld1]

There's also the question of float level. See www.amckayltd.com/carbguide.pdf for procedures. If you don't have inline fuel filters, install them.

 

[20ftollie]

Thanks for the replies. I pulled the bowl off the right side carb and the float and needle moved freely so I took the float off and inspected it for holes but didn't see anything. I cleaned everything up again and bent the tab on the float up maybe 1/16" at the most to see if it would help get the valve to shut. I filled the tank again and started it up and let it run for a few minutes. After I shut it off gas started leaking again same as before.

BUT, then I noticed the LEFT side petcock was dribbling gas out of the FRONT of the lever. I shut the gas off and pulled the hose. Sure enough gas was dripping from the petcock while it was turned to OFF. So now I'm thinking the issue is mostly the leaky petcock and I just need to replace the gasket inside of there and clean it up. Does that sound about right? I know it doesn't solve the carb problem but at least if the petcock is shutting off completely it won't allow any extra gas to get in there, correct?

Thanks
Matt

 

[jayel]

yes you need to get the petcocks to hold first then float level set correctly, then look verrry carefully at the brass tube in the float bowl that the overflow hose comes out of if it had any water in it and it froze it could have cracked that tube and it will drip the fuel in the bowl since the crack will be lower than the inlet tip of the tube for normal overflow protection

 

[jmink427]

Thanks for the replies. I pulled the bowl off the right side carb and the float and needle moved freely so I took the float off and inspected it for holes but didn't see anything. I cleaned everything up again and bent the tab on the float up maybe 1/16" at the most to see if it would help get the valve to shut. I filled the tank again and started it up and let it run for a few minutes. After I shut it off gas started leaking again same as before.

BUT, then I noticed the LEFT side petcock was dribbling gas out of the FRONT of the lever. I shut the gas off and pulled the hose. Sure enough gas was dripping from the petcock while it was turned to OFF. So now I'm thinking the issue is mostly the leaky petcock and I just need to replace the gasket inside of there and clean it up. Does that sound about right? I know it doesn't solve the carb problem but at least if the petcock is shutting off completely it won't allow any extra gas to get in there, correct?

Thanks
Matt

I have had my 75 for a few months now and it did the same thing... Rebuild or peplace the petcock......

 

[20ftollie]

Killer, thanks for the help. Jmink did you get the rebuild kit from MikesXS?

 

[jmink427]

I had to replace the whole petcock on mine. I was in bad shape, someone had JB welded it... Yes I got it from Mike's...

 

[5twins]

There is a large rubber disc under the petcock arm with 4 or 5 holes in it. That is what the arm seals against. It gets worn or sometimes torn up. Sometimes you can just flip it over so you now use the back undamaged side for sealing. Sometimes you can fix the petcock this way without replacing any parts.

 

[mouser]

does it do it when the bike is on the center stand.? Set your floats accurately to exactly what is recommend in the manual from the gasket surface. Sounds to me that you have two issues...perhaps. The petcock and poorly adjusted float and/or a poor seal on the needle it controls. You shouldn't be able to blow thru your fuel line with carbs full of gas, on the center stand if your floats and needles are functional