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Author Topic: Carb overflow is...well....OVERFLOWING!  (Read 3858 times)

Offline jbeebe

  • Posts: 102
Carb overflow is...well....OVERFLOWING!
« on: Nov 03, 2012, 21:17:48 »
Hey everyone, i've been lurking for a while, and didn't plan on posting until I could start a build thread. Well i've been doing less building and more repairing.

It's an 81 KZ440 with the CV carbs. they overflow out of the drain hole at the bottom of the bowl all the time. Here's what i'v done:

new valves (along with a full rebuild kit)
polished the brass valve seats beautifully so they aren't getting hung up
adjusted the float height. I set the fuel level lower than it should be, just to hopefully stop the overflow, but it didn't stop.
replaced drain screw o-rings.
checked the overflow tube in the bowl for cracks or leaks, it's all good.
the floats don't absorb any water, they are in good shape

So what the heck is jammin' me up over here in Cleveland!?!?

I'll reward the first reply with some pics of the bike.  ;)
« Last Edit: Nov 03, 2012, 21:21:48 by jbeebe »
81' KZ 440 brat/cafe

Offline teddpage

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Re: Carb overflow is...well....OVERFLOWING!
« Reply #1 on: Nov 03, 2012, 21:28:20 »
Hey!  Welcome.  Are you sure you adjusted the floats lower?  Ive seen a few people adjust them the wrong way.  It can be confusing.  I dont know if this is your first time working on carbs or not.
Like if you bend the tab on the float upwards (doing this by memory, so dont hold me to it), you are lowering the float and vice versa.  Might wana double check that since it seems you have everything else sorted.
1971 Honda CB450 Build -->> http://dotheton.com/index.php?topic=13854.0

"its a motor dude degrease the fucker and crack on" - axeugene27

Offline jbeebe

  • Posts: 102
Re: Carb overflow is...well....OVERFLOWING!
« Reply #2 on: Nov 03, 2012, 21:39:07 »
With the carbs upside-down, i bent the tang down, or in towards the valve to lower the fuel level. Once i put the carbs back in today, the fuel level was really low (~8mm below the mating surface, it should only be 3mm) so I bent the tang back "up" away from the valve a bit, thinking that the lower fuel level didn't help anyway. I have the FSM for it, but the wordage is still confusing sometimes, so correct me if i'm doing it wrong.

as promised:

it's nothing to look at now, only did repairs/maintenance and a little cosmetics. I want to sort out all the repairs before I start really mod'ing it into a budget brat-ish thing.

from day one to how it is now:







81' KZ 440 brat/cafe

Offline teddpage

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Re: Carb overflow is...well....OVERFLOWING!
« Reply #3 on: Nov 03, 2012, 21:44:50 »
Hmm...it sure sounds like you did it properly.  You replaced the float needle you said?  And is just one carb overflowing or both? 
1971 Honda CB450 Build -->> http://dotheton.com/index.php?topic=13854.0

"its a motor dude degrease the fucker and crack on" - axeugene27

Offline jbeebe

  • Posts: 102
Re: Carb overflow is...well....OVERFLOWING!
« Reply #4 on: Nov 03, 2012, 21:54:17 »
Hmm...it sure sounds like you did it properly.  You replaced the float needle you said?  And is just one carb overflowing or both? 

Both, but one leaks more than the other. Yup, new float needles with fresh and supple rubber tips, ready for the plugging.

I'm checking the float height the following way:

with the engine off and the petcock open, i open the drain screw and view the gas level through a clear tube alongside the carb while holding the bike up off the kick stand. Does the bike have to be cold for this, or doesn't it matter?
81' KZ 440 brat/cafe

Offline MotorbikeBruno

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    • Carb cleaning in MN
Re: Carb overflow is...well....OVERFLOWING!
« Reply #5 on: Nov 03, 2012, 22:19:20 »
My KZ550 had the ol' honda cb900/1000 Custom problem...which might plague you as well.  Make sure that your brass overflow tube doesn't have a hairline crack in it.  I polished the float valves, got new needles , changed float heights and it STILL leaked gas.  I found the crack, and soldered it up, no more leak! Might be your issue too.

Offline jbeebe

  • Posts: 102
Re: Carb overflow is...well....OVERFLOWING!
« Reply #6 on: Nov 03, 2012, 22:32:10 »
My KZ550 had the ol' honda cb900/1000 Custom problem...which might plague you as well.  Make sure that your brass overflow tube doesn't have a hairline crack in it.  I polished the float valves, got new needles , changed float heights and it STILL leaked gas.  I found the crack, and soldered it up, no more leak! Might be your issue too.

i pulled the bowls off the carb and filled them with water, no drip. So i'm guessing that there shouldn't be any cracks in the tube. right?
81' KZ 440 brat/cafe

Offline DJ_AX

  • Posts: 4
Re: Carb overflow is...well....OVERFLOWING!
« Reply #7 on: Nov 03, 2012, 23:12:24 »
... Make sure that your brass overflow tube doesn't have a hairline crack in it.  ...  I found the crack, and soldered it up, no more leak! Might be your issue too.
+1 ...
Those "hairline cracks" are sometimes thinner than a hair.
A quick fix for this is to put a snug tube/sleeve over the stand pipe.


And water is a different viscosity and may not leak where fuel might...

Offline Green199

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Re: Carb overflow is...well....OVERFLOWING!
« Reply #8 on: Nov 04, 2012, 07:11:25 »
+1 to check for hairline cracks.

I had the same problem. I found the easiest solution, apart from putting a tight sleeve over was to solder the crack up. Spent ages trying to diagnose the problem, and then 10 mins to fix it....isn't that always the way!
1973 CB250 'Doing it right this time round' - http://www.dotheton.com/forum/index.php?topic=36795.0

Offline HerrDeacon

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Re: Carb overflow is...well....OVERFLOWING!
« Reply #9 on: Nov 04, 2012, 07:23:06 »
To help isolate the issue, try taking the float bowl off and filling it with gas. If it leaks, there is a crack somewhere or the drain screw is not seating correctly (if your bowl is designed like this). If its fine, try keeping the bowl off and checking the float needle. Gently push the float up and turn on the petcock to see if its sealing correctly. Can get a bit messy but it allows you to see if its working correctly. If that's fine, the float may be getting hung up on the gasket or is not moving freely on the pivot.
Perry

1972 Honda CB350 K4 / 1978 Honda XL250S /1982 Honda MB5 / 2014 Honda CB500X