need a little help

Jim8208 · July 19, 2010, 05:12:18 PM

Hey guys,

I've got a problem with a leaky #1 carb and I can't seem to figure out what's causing the leak. I replaced the float valve and a new oring gasket as I thought that was why it was leaking. Anyway it seems it's something else. I made sure everything was clean in the float bowl. It appears that gas is leaking from above the float bowl as the fuel line that goes into the carb is wet with gas. I'm looking for some ideas as to what else could be the cause of my problem. I'd sure appreciate some of you more mechanical folks help with this. Thanks in advance for any info.

hootmon · July 19, 2010, 07:38:10 PM

I've been told (I don't know that it's true) but if one of the floats is leaking it can travel through an overflow tube and appear to be leaking in one of the other carbs..
IF you have the carbs out, you can feed the intake tube with fuel (from a bag or bottle) and with the float covers off, lift the 4 floats and see if they all stop leaking..

Not to depress you, but I have a friend that has a CB1000c and he has once cylinder that shoots gas out the bottom tube under the bike whenever the bike is running. We have replaced all of the needles, I've done the test stated above, made sure all the vent tubes were clear, made sure all the floats are good, and the bike still does the same thing.. So I would be interested in any solution that you come up with..

Jim8208 · July 19, 2010, 07:56:53 PM

Thanks for the info. I do have the carbs off (for the second time) and am pretty stumped at the moment as to what the problem is. I'll try what you suggested and see if that lets me know anything. It's almost like the carb is flooding badly, I guess that's how I'd describe it anyway. Thanks again and maybe someone else will chime in with some other ideas as well.

TLRam1 · July 19, 2010, 08:42:11 PM

Are any of your floats cracked and have gas inside?

Jim8208 · July 19, 2010, 09:33:03 PM

Quote from: TLRam1 on July 19, 2010, 08:42:11 PM
Are any of your floats cracked and have gas inside?

I don't think so but I'll certainly check them out.

hootmon · July 19, 2010, 09:44:49 PM

Quote from: TLRam1 on July 19, 2010, 08:42:11 PM
Are any of your floats cracked and have gas inside?

Put them in a bowl with Gas and something to hold them down under the gas for 20 minutes or so, then let them up and see if they float or have any fluid in them.

Jim8208 · July 19, 2010, 09:52:34 PM

Quote from: hootmon on July 19, 2010, 09:44:49 PM
Quote from: TLRam1 on July 19, 2010, 08:42:11 PM
Are any of your floats cracked and have gas inside?
Put them in a bowl with Gas and something to hold them down under the gas for 20 minutes or so, then let them up and see if they float or have any fluid in them.

Would it be a good idea to check all the carbs even though #1 is the only one leaking? I'm willing to do whatever it takes as long as it's necessary. I really appreciate the help.

John Luttrell · July 19, 2010, 10:31:57 PM

Have you checked to see if any of the spark plugs are looking gas fouled? If you have a carb float allowing too much fuel in a carb, the spark plug in that cylinder should be showing signs of flooding and look different than the other plugs. I mention this, because if none of your plugs show signs of running too rich, you are dealing with an external fuel leak from a fuel line and not a sticky float needle.

Jim8208 · July 20, 2010, 06:26:04 AM

Quote from: John Luttrell on July 19, 2010, 10:31:57 PM
Have you checked to see if any of the spark plugs are looking gas fouled? If you have a carb float allowing too much fuel in a carb, the spark plug in that cylinder should be showing signs of flooding and look different than the other plugs. I mention this, because if none of your plugs show signs of running too rich, you are dealing with an external fuel leak from a fuel line and not a sticky float needle.

Since I've had the carbs off I've changed the plugs. I looked the old plugs over and they all seem to be fine, none look to be be fouled. I suppose it is possible one of the fuel lines has a crack or is leaking somewhere. I really hadn't put much thought into that possibility but it does sound plausible as the tube leading into the carb is wet. Maybe a leaking line is dripping onto it? Thanks very much for the tip, hopefully I can get this thing fixed by the weekend.

One other thing, the petcock even in the off position still drips a little gas out of it. Could this in any way have anything to do with my problem? Maybe flooding the carb? Probably not but I just thought I'd toss that out there.

hootmon · July 20, 2010, 06:54:49 AM

Quote from: Jim8208 on July 20, 2010, 06:26:04 AM

One other thing, the petcock even in the off position still drips a little gas out of it. Could this in any way have anything to do with my problem? Maybe flooding the carb? Probably not but I just thought I'd toss that out there.

Unless you have done something to it, you should have a vacuum shut off valve just behind the right rear cylinder (1st stop after the petcock) that should prevent flooding if the pet cock leaks.. I leave my fuel on all the time and never had a flooding issue..

lragan · July 20, 2010, 10:46:31 AM

Quote from: hootmon on July 20, 2010, 06:54:49 AM
I leave my fuel on all the time and never had a flooding issue..

Likewise on both my '96 Magnas. And, both of the tanks drip gasoline with the valve on "off" position. Only an issue when I have the tanks off the bikes -- I stand them on their noses on a cloth (to avoid scratching the paint), and this seems to solve the problem.

Jim8208 · July 20, 2010, 03:37:28 PM

I checked the fuel lines and they seem to be good. Is it possible the tube that connects the carbs could be leaking? Is there an oring in there that could be bad? It looks like it could be leaking out of it and draining down onto the carb from what I can tell. Has anyone ever heard of this type of problem before? If by chance that could be the problem I guess that means I'll have to separate the carbs. I really don't want to do that but I will if that is what it takes.

John Luttrell · July 20, 2010, 09:21:44 PM

Yes, the fuel tubes between the carbs do have 'o' rings in them, at the carb body, that can leak; I have also heard of them getting small cracks or breaking while separating the carbs. If you did not separate the carb bodies from each other, the tubes should not be damaged, but it's not impossible for an 'o' ring to leak for no apparent reason either.

Jim8208 · July 20, 2010, 09:35:44 PM

Quote from: John Luttrell on July 20, 2010, 09:21:44 PM
Yes, the fuel tubes between the carbs do have 'o' rings in them, at the carb body, that can leak; I have also heard of them getting small cracks or breaking while separating the carbs. If you did not separate the carb bodies from each other, the tubes should not be damaged, but it's not impossible for an 'o' ring to leak for no apparent reason either.

John, I haven't separated the carb bodies from the tubes yet. If an o-ring is leaking how would I go about replacing it without causing any damage to the tubes?

John Luttrell · July 21, 2010, 09:19:32 AM

Well, you would need to replace the 'o' ring on both carbs that the tube connects to. I don't know if you are old enough to have worked on the old Holly 600cfm carburetors, but they had a similar tube between the front and rear float bowls and you would often have to replace the 'o' rings on that tube as well.

What you will need to do is, apply a small amount of petroleum jelly to the 'o' ring, then put it on the tube to where it is just barely on the end of the tube; this will allow the 'o' ring to roll into place as the tube is inserted into the carb body. If you don't do it this way, the 'o' ring will be pinched as you push the tube into the carb and will leak.