leaky overflows on keihin carbs... WHAT THE HELL!?

[maverik]

ever since the first day I bought my cb350 the stock keihin carb overflows have leaked like crazy...

first logical thought, lower the float height... didn't work. ok let's get weird and reeeally lower the float height to shut off fuel flow sooner... nope, still leaking out the overflows

then I thought hey! maybe the brass overflow tubes IN the bowls themselves are cracked. so I took the bowls off and filled them with water but NOPE, they hold liquid just fine without leaking.

THEN I reluctantly bought new needle and seats. I say "reluctantly" because the existing needles looked absolutely flawless and I couldn't justify spending the $40 on an iffy solution. anyway, BRAND NEW needle and seats installed, float height set exactly to specs for my motor, and STILL leaking just as bad.

WTF mate?!

 

[650hardtail]

did you check and see if any floats have gas in them ?

 

[maverik]

one of them did. I dried it out and patched the crack and so far the repair has held up.

with the carbs installed I took the bowls off, manually held up the needle with my finger then opened the petcock and no fuel came through the seat. as I let pressure off my finger the fuel started to flow just as it should. I don't get it.

 

[teazer]

Could be cracks in the copper overflow pipes in the bowls.

 

[maverik]

nope, I said i tested those in the original post. I filled the bowls up with water and they didn't leak at all

 

[teazer]

Gas will go through cracks that water just balls up and won't pass through.

Grab a spare bowl from ebay or somewhere and modify one to check the FUEL level in the bowl . It should be around 3mm below the gasket face.

 

[maverik]

Gas will go through cracks that water just balls up and won't pass through.

just redid the bowl test. sure enough, the inner overflow tube has some hairline cracks. I guess I didn't even think about the difference in viscosities. problem solved... thanks man!

 

[teazer]

No worries mate. Just get a thin wall brass tube from your local model/hardware store and solder them in.

 

[maverik]

yeah I went to ace (also where I got the brass rod for a float pin replacement) and picked up some tubing. I was thinking of it as a temporary solution though, so I just slopped JB weld over the existing tube and slid the new one over. it seemed to be a nice snug fit. supposedly JB weld is impervious to gas so i don't see why it won't work.

 

[mothgils]

I had the same issues. I got some small gas engine tubing and then cut it just short of the top of the overflow tube. I slid it down all the way and it seems to do the trick.