Leaky carb question!

[alex l]

Hey, Just picked up a '75 650xs in great condition. The only problem (so far) is that gas is leaking out of the right overflow tube from my carbs. I assume that i just need to clean the carbs and unstick the float somehow, but a few people have suggested that it might be the petcock. Last time i switched the petcock to "off", it left some gas on my fingers, but i can't see any gas dripping from the petcock faceplate itself. Basically i'm just wondering if anybody had any ideas about how to eliminate the petcock as a problem, cause i really don't want to have to deal with that AND the carbs. Any advice is appreciated, thanks!
-Alex

 

[5twins]

Your petcock may need a rebuild. There are rubber parts in there that seal it but can wear out eventually. Pull the gas line off it and see if it stops flowing fuel when in the "Off" position. Sometimes you can pull the arm out and just flip the rubber disc over that's under it. That gives a fresh side for the arm to seal against.

 

[Hairyblackdude]

I don't think a leaky petcock would cause the carb to overflow..

The carb floats should shut off gas flow thru the needle valve in the carb. If this were not the case, every person without a vacuum operated petcock would have overflowing carbs.

I just had gas dumping out of my left carb last week... Warmed the bike up for several minutes, geared up & made it about a block before she started sputtering.. Glanced down to see the gas waterfall from the air filter. Limped her back to my shop.

With the carbs still mounted, I pulled the bowl off the offending carb. Turned the petcock back on, let gas start leaking and lifted the carb float with my finger to make sure it was shutting off the gas- It was.

Remounted the bowl, turned gas on, still leaking..

Popped the bowl back off & removed the float... threw it into a container of water.. one side of the float was not "floating".. Holding the float in my hand, I can hear the gas INSIDE the float when shaking it.

My carb float developed a leak in the 10 minutes it took me to get ready.. It happens!!

So, remove the carb bowls, mount them up & make a mess !!

 

[XSLeo]

The float valve is not a fuel shut of device. If it where then they wouldn't put a petcock on there. The float and valve are a metering device. It is designed to keep the fuel in the float bowl at a certain level while the bike is running.
If the pet cock leaks the weight of fuel in the tank can cause fuel the leak past the float valve. If your bike sets in the sun the heat build up can cause fuel to leak past the float valve.
Any moisture that collects in the bottom of the tank gets into the petcock and can corrode the aluminum parts. There is a rubber disc inside. This disc has holes in it that are opened and closed as you turn the petcock on/off. The lever you turn has a flat disc that sets against the rubber disc. The flat part has a groove in it that connects the holes in the disc to control fuel flow.
If corrosion builds up on the flat part that sets against the disc it can rough up the rubber enough that it won't seal well. This is where the fuel you get on your fingers comes from.
To fix you remove your pet cock, tear it apart polish the flat surface with 400 grit or finer sandpaper till smooth, bright and shiny. Put the sand paper on something flat and be careful to keep the flat surface of the petcock part flat.
I had the same problem on my 75.
Also remember to shut the petcock off everytime you turn the bike off. This will prevent fuel leaks at the carb while not riding the bike.
Because you have the fuel running out the over flow your float valve in the carbs are not sealing. It is probably dirty float valves, or mis adjuste or leaking floats. Need the remove, clean, inspect the carbs.
www.amckayltd.com/carbguide.pdf will help with that.
Leo

 

[Hairyblackdude]

If your carb is leaking gas, you shouldn't START at the petcock.

Bottom line, the needle valve is not doing it's job. You just need to find out why.

How many people do you think actually shut off their gas when they are currently not riding their bike?

 

[cra-z1]

If you don't turn the gas off after each ride you stand the chance of fuel running into your intake down the valves and into the combustion chamber and possibly into the crank if left for a period of time. It's just a good practice to turn off the petcocks when not riding the bike.

 

[5twins]

He wanted to know how to eliminate the petcock as a problem, so I told him. He was already aware that the float needed looking at.

If you have manual petcocks, you must train yourself to shut them off any time you park the bike. It must become a habit and second nature. When you park your car, do you walk away leaving the keys in the ignition? Shutting your petcocks off should become just as much of a habit as taking your keys with you when you park your car.

 

[XSLeo]

The OP stated a gas was flowing out of the over flow, that is bad floats or float valves. He also siad he was getting gas on his fingers when turning the petcock. My responce covered both items.
Leo

 

[alex l]

Thanks for all the help. Since i don't know how long ago (if ever) the carbs or petcock were serviced it's probably a good idea to take a look at both of them. The petcock is probably letting a little of fuel through, as well as the float sticking.