Topic: Gas leak puzzler??

[MikeJW]

Last time I rode my 1972 750K was Saturday morning. Since then, it's been on center stand on a large concrete pad. A couple months ago, I completely rebuilt my petcock. After I put it back on the tank I removed my carbs and set the float levels as carefully as I could. About noon today, I noticed a wet spot on the concrete on the right side; not under the bike but beside it. Tracing the origin of the leak, I found it came from the front opening in the bottom of the airbox. I took the bottom half off and found about a half oz of gas in the bottom of the airbox. What the heck?? I did a SEARCH and only found one other mention of such a thing and it didn't seem to be similar circumstances to mine. Can anyone explain this to me, please?
MikeinMemphis

[Bob Wessner]

Perhaps a speck of something stuck between the float valve and its seat in one of the carbs? What is the condition of the fuel tank interior, is the petcock filter still in place?

[MikeJW]

To answer in reverse order; yes, I bought every part for the petcock that was available, including a new petcock filter screen. If there was something interfering with one or more fuel shutoff valves, why isn't it leaking out the overflow tubes? I think the inside of the tank is clean. This bike has never set up, unridden for long periods in its life.
Mike

[bollingball]

Bob how does it get in the airbox I thought it would go out the overflow tubes I have heard other people complain of this but I do not understand it.

[Bob Wessner]

Bob how does it get in the airbox I thought it would go out the overflow tubes I have heard other people complain of this but I do not understand it.

I don't quite understand that part myself, though I too have seen references to it, particularly with the bike on its center stand which would elevate the rear somewhat. I was really just addressing a possible source for the seepage from the carb.

[MikeJW]

I always park it (at home) on the center stand and I always turn the petcock off when it's not running. Trying to understand the leak but also concerned about how gas is even getting to the carbs with a recently rebuilt petcock turned OFF
Mike

[Johnie]

So when you rebuilt it did you also replace those gaskets on the 2 screws that hold the petcock to the tank? If so, what did you replace those with? Fiber, rubber or what?

[MikeJW]

No, I didn't, for two reasons:
1. I couldn't find replacements
2. mine seemed (looked) in pretty good shape
Mike

[TwoTired]

Have you checked to see if the overflow tubes are blocked?

[MikeJW]

Yes, checked, they are not blocked. Actually, my first thought.

[Johnie]

Check out this similiar thread:
http://forums.sohc4.net/index.php?topic=77408.msg863791#msg863791

[MikeJW]

Thanks, Johnie. That was a good thread and may be what I am experiencing. Where did you get those tight-fitting fiber washers? Sounds like I need to get some. Thanks
Mike

[Johnie]

Thanks, Johnie. That was a good thread and may be what I am experiencing. Where did you get those tight-fitting fiber washers? Sounds like I need to get some. Thanks
Mike

I got them at the local hardware store. Bring a screw in with you. Like I said, mine were a tight fit that I had to screw the gaskets on past the threads. But I used them on 3 bikes and none leak.

[MikeJW]

Well, I went to remove my petcock this morning and when I pulled down on one of the fuel hoses (the forward one), the whole little brass outlet tube came out of the petcock and stayed inside the hose. This may not be my main problem but obviously a factor. Now, my question is- should I try to cement it back in the petcock some way or start thinking about a whole new petcock? From some of the posts, I assume it can be difficult finding exactly the right petcock for a particular tank. Any suggestions? Thanks
MikeinMemphis

[Bob Wessner]

I believe the brass outlet nipple is a press fit (someone will chime in if I'm wrong). If it is, you should be able to gently tap it back in to the petcock base. Just make sure you don't mangle it.

[j squared]

I did that exact same thing on one of my hoses this past weekend!  Pissed me off, thought i had to buy a new petcock haha.  In a fit if rage i hammered it back in and hooked the line up and it seems all is well, so Im glad they are just press fit and I was actually OK

[Bob Wessner]

You lucked out. Usually, rage = mangle, guess how I know. 

[MikeJW]

Great, thanks, guys. I hope you're right. I've been sweating trying to figure how to hold it in the petcock. My fuel hoses have always been a tight fit...hard to get on, even harder to get off.
Mike

[bollingball]

You can chuck it up in a soft jaw vise and start in with fingers then get a Popsicle stick on the end tap the wood gently

[MikeJW]

I tried putting it into the petcock and it went in far too easily. No tapping required...thumb pressure only. Makes me think it needs some type adhesive on it when putting it back. Just don't know what the best choice would be

[bollingball]

You said it went "far to easy" but did it go all the way or do you think some of it broke off. If you think all is lost then you have nothing to loose clean everything good put it back in as far as it will go and  JB weld it using nothing larger than a pencil  or a piece of #12 copper wire it won't take much once you do this you are committed

[j squared]

If mine comes out again the next time I pull the line off I plan to use some red loctite in there, and failing that, some good ol JB Weld.

[Bob Wessner]

I tried putting it into the petcock and it went in far too easily. No tapping required...thumb pressure only. Makes me think it needs some type adhesive on it when putting it back. Just don't know what the best choice would be

Follow Bollingball's advice. If you just pushed it in with your finger, it's probably not seated tightly.

[MikeJW]

No, none of it broke off. It went all the way in, just too easily. I think it would still leak if used as is. A word of warning to anyone reading this. JBWeld is NOT resistant to gasoline. After awhile, it will break down and just become a mess. That's even if you let it harden for a couple days before exposing it to gas. I have thoroughly proven this to myself in the past and don't plan to try it again. There must be some sort of automotive gasket compound that will harden up and resist gas. I just have to find it.

[TwoTired]

There is a variant of Locktite that will withstand gas, I think.
Loctite red 271 for example.

http://www.loctiteproducts.com/products.shtml