82 750K is hemorrhaging fuel

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82 750K is hemorrhaging fuel

jonktay
This post was updated on .
Hey everyone,
Just bought an '82 CB750K, my first project bike. Not all cyclinders were running so I decided to rebuild the carburetor. My only previous engine experience has been with aviation turbine engines, which notably do not have carburetors.... So naturally this thing has become the bane of my existence.

Before the rebuild cylinder 1,3,4 were firing. Electrics are good but now only the #4 cylinder is firing, and I have a gut suspicion that this has something to do with the fuel that is hemorrhaging out of the bike anytime fuel is turned on. Fuel is coming out of the bowl drains, what I believe is the vacuum shutoff valve (photo attached, has no barb), and at times the "t-fitting" between the carbs. The floats in this bike are not adjustable, and I've replaced the floats and the float pins.

I have two specific questions regarding this, why would fuel be coming out of the vents, and is there a good diagram showing to reconnect the cb750k carb hoses? I'll attach the diagram I'm using, it looks slightly different than my carb and I want to make sure I'm not inducing my own problem.

Thanks in advance!
 
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Re: 82 750K is hemorrhaging fuel

TOOLS1
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It looks like you have the lines correct. What is probably going on here is that the float needles are not sealing in their seats. Try cleaning the seats with a Q-tip and brass/chrome polish. You can adjust the floats by carefully bending the little metal tab. Here is a link to our thread on cleaning adjusting carbs. http://honda-cb750-s.456789.n3.nabble.com/Cleaning-and-adjusting-a-carberaters-best-videos-for-dummies-This-ought-to-be-pinned-at-the-top-td3905817.html 
And this one of the links that is in that thread to a great write up on another forum.
http://deuceswild.yuku.com/topic/903/Carb-Cleaning#.WC9e1Mnpxi9
TOOLS
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1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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Re: 82 750K is hemorrhaging fuel

motogrady
In reply to this post by jonktay

Me thinks maybe debris in the petrol tank.
Or, when you put the float bowels back on the float needles got kinda jammed, or cocked so they don't seat.
Or you have the floats in upside down.
Or, like tools said, there's a bit of crap between the float needle and its seat.

With a real small Phillips, you can drop the float bowels whilst the carbs are still on the bike.
I'd take em off, put a towel under them, turn on the petcock, an lift the floats one at a time, rather quickly,
to see if the petrol stops flowing when you do.

Rubber hoses degrade, petcock gaskets get brittle, crap accumulates in the fuel tank itself.
Any of that gets in the way of the float needle seating snugly, you get exactly what you are experiencing.

After cleaning mine, it was new hoses, and a clear plastic in line fuel filter, from the lawnmower department
at Lowes, installed right before carb rack, that was the fix on this one.
Maz
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Re: 82 750K is hemorrhaging fuel

Maz
In reply to this post by jonktay
Another possible cause is that the thin brass overflow tubes inside the float bowls are cracked / loose / missing.

Maz
'76 CB500T
'75 GL1000 'Wing
'79 CB750L
'90 FJ1200
'93 GS500E

In a little place called Bexley, Kent, UK (Just south of London!)
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Re: 82 750K is hemorrhaging fuel

jonktay
In reply to this post by jonktay
Thanks for the quick feedback! The looks like my replacement float needles were the issue, or at least part of it. Putting it back together this weekend, I'll update how it goes!
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Re: 82 750K is hemorrhaging fuel

bingtx
Did you get it fixed?