Topic: Gas Leak From Overflow Tube

[sm8]

So I recently noticed a gas smell in my garage. I noticed a slight gas leak coming from the overflow tube. My carbs were recently rebuilt and the bike runs great. I ran the bike for 10 miles. Stopped and checked. No leaking. But when I got home and checked it again a few hours later I noticed a leak again. The petcock is off. I always run the bike with the petcock off for 30 seconds just before shutting down to drain any excess fuel. So why would this be happening? I've seen a couple people say run some seafoam through the tank. Yes or No? Any other simple things I can try to remedy the problem? Thanks for the help!

[Stev-o]

The overflow tube in you float bowl may have a crack. Pull the bowl and fill it with gas to check it. I've had this issue a couple times [different bikes] and just replaced the float bowl.

[Davidov]

I had a similar issue with my 750F.
My particular issue was a tiny piece of debris (rust, dirt?) that was sitting on top of the rubber tip of the float needle.

Your floats could be sticking on the arm. If it acts up again, try tapping on that specific carb (with something like wood or plastic) and see if it stops overflowing.

[HondanutRider]

Your petcock isn't turning off, and one or more of your float valves isn't shutting off.  Alternately, besides the leaking petcock, the overflow tube in whichever carb is leaking may have a crack as described instead of a bad float valve.. 

However, if as you say the petcock is closed with the leak, then it isn't shutting off.  You can confirm this by disconnecting the outlets and see if anything dribbles out with it shut off.  If so, then perhaps the gasket/washer in it is shot or else the whole petcock body is bad.

[sm8]

I think you are right. I removed the bowl and could see very small lines on the brass fitting inside the bowl. I'm guessing this is where it's leaking from? With the bowl off and the petcock closed there wasn't any fuel leaking so I don't think it's the petcock.
So where would I find a replacement float bowl? It's only leaking out of the #1 carb.
Thanks for all the help!

The overflow tube in you float bowl may have a crack. Pull the bowl and fill it with gas to check it. I've had this issue a couple times [different bikes] and just replaced the float bowl.

[Tempast]

I had small cracks on all four on my CB550. My dad soldered the outside of the tube and It's been fine for 5 years now.

[Stev-o]

I think you are right. I removed the bowl and could see very small lines on the brass fitting inside the bowl. I'm guessing this is where it's leaking from? With the bowl off and the petcock closed there wasn't any fuel leaking so I don't think it's the petcock.
So where would I find a replacement float bowl? It's only leaking out of the #1 carb.
Thanks for all the help!

The overflow tube in you float bowl may have a crack. Pull the bowl and fill it with gas to check it. I've had this issue a couple times [different bikes] and just replaced the float bowl.

Forum member Haris rebuilds carbs and sells parts.  PM him here.....


http://forums.sohc4.net/index.php?topic=105640.0

[sm8]

Ok, so now I'm second guessing the bowl as the issue. I took the bowl out and filled it with water to see if there was a leak. There weren't any visible leaks, but there were very small bubbles at the bottom of the brass overflow tube. But, after putting everything back together (the float bowl was completely dry) I went back out a couple hours later and there was a little gas in the bottom of the bowl. The petcock is off, but should there be a little fuel flowing it at all? With the bowl removed there aren't any visible leaks from the float. When i move the float up and down there is a tiny dribble, but nothing crazy. I don't even need a rag.

What else should i be considering or looking at?

Thanks

[BobbyR]

You can pinch off the gas line after the petcock with a vise grip if the bowls stay full it is the petcock.

[sm8]

Just a thought. Wouldn't I have a leak from other carbs if it is a leaky petcock? It's only leaking from #1.

You can pinch off the gas line after the petcock with a vise grip if the bowls stay full it is the petcock.

[flybox1]

Just a thought. Wouldn't I have a leak from other carbs if it is a leaky petcock? It's only leaking from #1.

You can pinch off the gas line after the petcock with a vise grip if the bowls stay full it is the petcock.

even with a leaky petcock, your floats should stop the flow of gas
if only #1 is leaking, the float and its seat are not functioning properly, either from an incorrect float height, a blocked or improperly seating float valve, or a cracked stand pipe.
fix both the petcock and the float valve issue.

[AbbyRider]

I had this same issue and it wasn't the overflow tube. It was a corroded drain screw. I replaced the drain screw with a new one and it solved the issue for me.

As a side note - I remember reading that someone had fixed a cracked overflow tube with shrink tubing. Slid a piece over and used a heat gun to shrink in place.

[flybox1]

As a side note - I remember reading that someone had fixed a cracked overflow tube with shrink tubing. Slid a piece over and used a heat gun to shrink in place.

probably, but find that member and ask him/her how it lasted being submerged in gas.  id be curious.
Id prefer installing a section of brass tubing over the stand pipe

[AbbyRider]

probably, but find that member and ask him/her how it lasted being submerged in gas.  id be curious.
Id prefer installing a section of brass tubing over the stand pipe
[/quote]
It was Aaron in Wisconsin. As of the time of his post it had lasted two years, but don't know if it's still holding up. A few others have checked after a year and it's still holding. Probably depends on the quality of the shrink tube, but heck, even as a short term solution it's worth doing just to see if it solves the issue. If it doesn't, it's at least crossed one of them off the list.

[dusterdude]

I tried to find brass tubing to put over my stand pipes and couldnt find anything close,is there a size that works?

[sm8]

Is it possible to check float height with the carbs on the bike? I'd like to try that first before I order another rebuild kit. These carbs were just rebuilt 1,000 miles ago by a guy who knows his stuff. The bike runs great and didn't leak until a couple days ago. Is it possible that the float height got tweaked?

[Stev-o]

Is it possible to check float height with the carbs on the bike?

Yes, use the clear tube method...


http://forums.sohc4.net/index.php?topic=135470.0

[flybox1]

I tried to find brass tubing to put over my stand pipes and couldnt find anything close,is there a size that works?

I dont remember what the OD of the stand pipe is, but hobby shops sell brass tubing in a variety of metric ID's.
its gotta be 3mm +/-

[Stev-o]

I tried to find brass tubing to put over my stand pipes and couldnt find anything close,is there a size that works?

I dont remember what the OD of the stand pipe is, but hobby shops sell brass tubing in a variety of metric ID's.
its gotta be 3mm +/-

Just measured one....2.5 mm.   I have a spare bowl if you are in need [750]

[sm8]

Turned out to be the float height. I adjusted ever so slightly and it solved the problem. Thanks for all the advice. Now I know what I'm looking at and for if and when this happens down the road.

[BobbyR]

Congratulations 

[71NOVADUDE]

I tried to find brass tubing to put over my stand pipes and couldnt find anything close,is there a size that works?

I found brass tubing for my bike at a Hobby Store that dealt with model airplanes and cars. I think it was around 1/8 inch.

[dusterdude]

Ill keep that in mind for the future,i was fortunate enough to find a set of carbs at a swap meet last year and the bowls all had good stand pipes

[sm8]

Well Crap...I spoke too soon. Still leaking a small amount of gas overnight. Yesterday just to check, I swapped the floats and needles between Carb #1 and #4. Ran the bike for 25 miles. Ran excellent. No leaks. Then this morning #1 is leaking again. I removed the bowl and it was overflowing with gas. So its not the float or needle.
Could it be the needle seat??

The carbs were just rebuilt within the last thousand miles or so. I'm getting frustrated now. Today I decided to disconnect the petcock from the carbs. I hooked up an aux hose from the petcock and closed it off so it wouldn't continue to leak. I'll start the watching and waiting process again. 

Here is my question. Even if the petcock has a small leak, why wouldn't the float shutoff the flow of fuel? I've forgotten the petcock on a time or two and never had an overflow leak. The only sense I can make of the leaky petcock only coming from #1 is that I park the bike on the side stand. So gravity flows down to carb #1.

Thoughts??

[Vinhead1957]

Did you swap the valve seats too?   You could have junk in the line to that carb