Author Topic: 4 cable carbs occasionally spit gas out of overflow  (Read 420 times)

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Offline jakec

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4 cable carbs occasionally spit gas out of overflow
« on: August 07, 2025, 05:38:47 PM »
I have early style carbs (mid year diecast) with 4 cables. 2 years ago I spent a lot time getting them set up just right. The bike still runs great and idles low at 900rpm. At that time I got all new genuine Honda valves and seats. My question is related to this issue that comes and goes. Sometimes when I’m at a stop like I can look down and see a substantial amount of gas squirting out of the overflow hose.

After riding I figured out it was #3. The hoses are all various lengths and I can see one is wet and the others are dry. Anyways, I was wondering if one possible explanation would be heat? The #3 hose was touching the exhaust. Could this lead to air expansion in the bowl? I was thinking about trimming about 3/4” off of a couple hoses.
1970 CB750 K0
1977 CB750 Chop
1984 Big Twin Evo Chop
1997 XR650L

Offline 69cb750

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Re: 4 cable carbs occasionally spit gas out of overflow
« Reply #1 on: August 07, 2025, 05:47:29 PM »
Quote
After riding I figured out it was #3. The hoses are all various lengths and I can see one is wet and the others are dry.
Anyways, I was wondering if one possible explanation would be heat? The #3 hose was touching the exhaust. Could this lead to air expansion in the bowl?
No and no.
Either float, float level or valve and seat.
If valves are oem Honda, shake float, I've had several fail with gas in float.
If float good, adjust tang to lower gas level a smidge.

Offline jakec

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Re: 4 cable carbs occasionally spit gas out of overflow
« Reply #2 on: August 07, 2025, 06:50:13 PM »
The floats are the black ones that are solid. And the leak only happens in little squirts ever 10 seconds or so, not a constant flow.
1970 CB750 K0
1977 CB750 Chop
1984 Big Twin Evo Chop
1997 XR650L

Offline MauiK3

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Re: 4 cable carbs occasionally spit gas out of overflow
« Reply #3 on: August 07, 2025, 06:58:17 PM »
Sounds like a float hangs a bit, read “Thoughts of Hondaman”, there is a section about this, it is also in his book.
1973 CB 750 K3
10/72 build Z1 Kawasaki