Leaking Float Bowl Overflow Tubes

[Nessism]

I'm rebuilding a set of Keihin CV34 carbs from a KZ750/4 and struggling with leaking out the overflow tubes. Found that the overflow tube was cracked on three of four carbs, now fixed by soldering, only one of the tubes is also leaking where it goes though the hole in the float bowl.

The 1980 version of these carbs have functional overflow tubes, and for the 1981 model year the feature was deleted. I've seen some later year float bowls without the tubes and others with the tubes only the nipple on the bottom of the float bowl wasn't drilled. The set I'm working on are actually the later, only some knucklehead (me) drilled out the nipple making the overflow functional (bad idea). Well, maybe not a bad idea per say only now I've got leaking that needs to be fixed.

I'm thinking about the following options to fix the carbs:

- Use fuel tank sealer around the leaking tube. I've got access to some high tech aircraft tank sealer stuff that's state of the art (P/S 890 Proseal).

- Cut off the tubes and plug the hole in the float bowl with...something. Any ideas?

- Replace the tubes.

Any suggestions?

 

[Sandy]

Pull the tube out, tap the hole and use a small screw and fibre washer.

 

[Brendan W]

I would prefer to have overflow going outside than in.
Is the problem that the fourth tube is cracked too close to (or inside )the housing to get solder on it ?
Could that tube be simply turned around to get the crack into clear air.
Only thing about sealer in there is it better be the good stuff 'cause you know where it's headed if it starts to break up.

 

[Nessism]

I would prefer to have overflow going outside than in.

Agree. That's why I made the tubes functional in the first place.

Did a leak test and bubbles come up from right where the tube enters the float bowl. Most likely the crack extends down into the float bowl.

Found a little tutorial on how to replace the tubes. Think I'll try this before trying to plug the hole...http://cx500forum.com/forum/general-discussion/7662-float-bowl-overflow-tube-raplacement.html

 

[Guest]

The only thing I would add is a tad bit if heat on the bowl part when pressing in the tube.
That was an excellent tutorial.

 

[Brendan W]

Yeah I was impressed with the work.

 

[Nessism]

The CX500 tutorial worked a treat! Piece of cake!

Used the dimple on the side of a threading die to help roll over the lip on the tubing to shrink the hole size. Flared the tubing OD using a drill on the inside just like the tutorial.

One down. Now I'm going to do the other tubes that I brazed. This fix is better...

Ain't the internet great!

 

[Guest]

The dimple on the die is a stroke of genius also.

 

[Nessism]

Factory on the right, homemade on the left.


P1030567 by nessism, on Flickr

 

[chuck hahn]

Have you checked for leaks?? Put a piece of vacuum hose on the bottom and fill the bowl with water and blow on the hose. Any leaks will make bubbles on the inside.

 

[Nessism]

Yes, checked for leaks. The new tubes are fine.

 

[steve murdoch]

Nice work, Ed.
Where did you get the new tubing? Hobby shop?

 

[Nessism]

Hobby shops that cater to the RC crowd will have it. I actually had a few pieces left over from when I used to fly RC. My local ACE hardware had some too. K&S is the common brand.

 

[Brendan W]

Hobby shops that cater to the RC crowd will have it. I actually had a few pieces left over from when I used to fly RC. My local ACE hardware had some too. K&S is the common brand.

Two signs you are over 50.
Using punctuation in texts and saying RC instead of drone.
Kids these days are merciless.

 

[Nessism]

Today's project was making a fuel Tee. Salty_Monk (Dan) loaned me his mini lathe and I did the rest...

P1030580 by nessism, on Flickr

 

[80GS850GBob]

Two signs you are over 50.
Using punctuation in texts and saying RC instead of drone.
Kids these days are merciless.

"Over 50"{old}...I prefer "wiser". "RC" is still alive and well{line control/boating/park flyers/scale/cars...}...drones are just the new thing.

 

[80GS850GBob]

Agree. That's why I made the tubes functional in the first place.

Did a leak test and bubbles come up from right where the tube enters the float bowl. Most likely the crack extends down into the float bowl.

Found a little tutorial on how to replace the tubes. Think I'll try this before trying to plug the hole...http://cx500forum.com/forum/general-discussion/7662-float-bowl-overflow-tube-raplacement.html

I might add a twist to that round over trick....torch the end of the brass to cherry red to soften it...takes just a moment of that to work. Then form in your homemade die. The tube stock isn't very flexible without kinking...in tighter bends. I've used this on my motorcycles for custom pipes...1/16 scale bikes that is... I made the reverse of that jig to flare the ends for scale model fuel injection stacks...{ah...other hobbies...}

 

[Nessism]

Since I still have Dan's lathe I decided to make a second Tee to have as a backup. Second time through I knew exactly what to do and the turning was even better than the first. Brazed on the nipple but wound up with a little silver drip so decided to clean that up with a file. Clamped the Tee in the vice to hold it while filing and used a little too much force, distorting it. Junk. The wall thickness in the area of the O-ring grooves was thinner than I thought. It was 98% finished and the Tee was dimensionally perfect. About 3 hours of my life down the drain. Live and learn.

 

[Steve]

About 3 hours of my life down the drain. Live and learn.

You were lucky that it failed on the bench, rather than on the road. :encouragement:

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