Topic: HELP!! fuel is coming from carb vent tube!

[amacemon]

I have a 72 CB750k2.  I have had it for about a month and finally, or so I thought, got it running well.  I went for about a 150 mile ride on Saturday with no issues at all!  Anyway, I went to the store yesterday and turned the fuel petcock off while I was in the store. I forgot to turn it back on until it started sputtering on the drive home.  No big deal, I thought, so I reached down and turned the fuel back on.

When I pulled in the driveway, there was fuel dumping out of one of the vent tubes.  No, it isn't one of the overflow tubes. It stopped when I turned the petcock off.  Then, later after the bike cooled down, I turned the fuel back on and it came out of the vent tube again.  I understand what is happening when the fuel comes out of the overflow tubes, but don't understand what is going on in this case.

Any ideas?

[amacemon]

bump. I could really use some help guys. I don't understand why it was working very well and now it is un rideable

[Tews19]

Most likely a stuck float. Remove the bowl. See if the float is hung up on anything. Then see if the problem continues

[goldarrow]

Try tapping the carbs with rubber mallet or fist (be sure to wear rubber gloves) and see if that stop overflow

[amacemon]

It isn't coming from the overflow tubes like i would expect a stuck float to manifest itself.  It is coming from one of the two vent tubes at the top of the carbs. Would a stuck float really behave this way?  Thanks for the replies, by the way.

[Davidov]

What model bike and what carbs are you dealing with?

[amacemon]

So, I just tried hitting the carbs with the back of a screwdriver and a rubber mallet as you guys suggested.  I turned on the fuel, and it leaked out the vent tube again.  The vent tube that was leaking was the one for carbs 3 and 4.  So, I started thinking...maybe carb 4 float is stuck, but the overflow tube is blocked which is causing the fuel to backup into the vent tube.  Could that happen?  I had an issue earlier with carb 3 overflowing due to a stuck float, so I new the overflow tube wasn't blocked.   

Anyway, I blew into the overflow tubes for both 3 and 4 until I could see air bubbles coming out  of the vent tube(it was sitting in a jar of gas that had leaked out)  After I made sure both were clear, I turned the gas back on and it didn't leak!

Have you guys ever heard of this happening?  I'm thinking I need to do a better job of cleaning the bowls than I did last time.  What is some good carb cleaner that I can soak the bowls in?  Last time I used brake cleaner.

[Davidov]

That does sound odd.
You should take the bowls off each carb and make sure there is no debris on the needles that seal the fuel inlet.

[Tews19]

I would take the carbs off and give them a really good cleaning.  I use this to soak all carb parts. You may have this problem ailing you all summer. Also make sure the tank is really clean as well. I use vinegar to clean out tanks. Cheap but effective. May take longer but one can't beat 13 bucks for 5 gallons of vinegar.

[MiGhost]

All it takes is a very small piece of dirt, grit, or a tiny flake of rust\varnish to plug the overflow tubes. Smaller than what the float valve screen will filter. Once the overflow is plugged. The fuel will go to the next open source which is the vent tubes.

Do you have an inline filter on the bike?
Is the tank clean, and free of rust?

[amacemon]

There is a sock type filter over the pickup inside the gas tank.  There is a small amount of rust in the tank, maybe I should take care of that too.  I was hoping that derusting the tank would be more of a winter project, though. 

This afternoon, I'm going to buy some carb cleaner that I can soak the bowls in to clean them out good.  Maybe that will fix my issue?

[flybox1]

the best solution to cleaning carbs is to hand clean them.
bowls off, jets and slides out, and clean them.  bottle brushes, flat brushes, wires for poking in jet holes, compressed air, carb cleaner spray and simple green.  soaking is fine for getting crud off, but it doesnt really get in there and clean the little holes and passages like you need for good operating carbs.  spray thru all the holes and get them spotless.

garbage in, garbage out -  if your tank is full of rust, even light rust, you cant expect your carbs to always operate properly with that stuff floating around.  if its light rust, do a forum search for "the works" or "prep-n-etch'  for tank treatments.  half a day and you're done.
if your tank has a fuel filter sock on the petcock, you cant assume its in good working condition(no holes) unless you take it out.
 treat your tank while you're cleaning your carbs, and youll be on the road the next day.