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Author Topic: 1972 CB500 Air Pockets in Fuel Lines  (Read 635 times)

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Offline wpadgett2

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1972 CB500 Air Pockets in Fuel Lines
« on: September 15, 2013, 06:40:09 PM »
        So this is my first post! I would like to start off by saying that the bike seems to be running fine but I keep developing air pockets in my fuel and it annoys me. I have managed to remove the pockets but as soon I start and run the bike they develop again. So I guess my question is what do you think is causing this to happen and is it even worth worrying about?
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Offline 754

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Re: 1972 CB500 Air Pockets in Fuel Lines
« Reply #1 on: September 15, 2013, 06:44:35 PM »
Switch to black fuel line..
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Offline wpadgett2

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Re: 1972 CB500 Air Pockets in Fuel Lines
« Reply #2 on: September 15, 2013, 06:52:46 PM »
That's pretty good advice!
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Offline TwoTired

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Re: 1972 CB500 Air Pockets in Fuel Lines
« Reply #3 on: September 15, 2013, 07:07:17 PM »
It is a gravity fed fuel system which feeds the top of a carb fuel bowl.  The float system always keep air at the top of the bowl chamber, so when the float valve opens, air enters the fuel line.  The stock fuel line routing allows air entering the feed lines at the float valve to rise to the fuel tank valve/drain point, to the surface of the fuel inside the tank, and not accumulate to effect fuel flow.

Long fuel lines that trap the air, violate the simple design of a gravity feed system.
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Offline wpadgett2

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Re: 1972 CB500 Air Pockets in Fuel Lines
« Reply #4 on: September 15, 2013, 07:23:29 PM »
Thank you TT for that explanation!
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Black 750K8

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Re: 1972 CB500 Air Pockets in Fuel Lines
« Reply #5 on: September 15, 2013, 07:46:42 PM »
So in other words take out any loops or uphill areas by shortening the fuel line and remove any redundant filters they are not necessary with the in tank filter Honda provides.
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Offline wpadgett2

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Re: 1972 CB500 Air Pockets in Fuel Lines
« Reply #6 on: September 15, 2013, 07:59:29 PM »
     I don't have any filters other than the one in the petcock. I'll check for excessive length and improper routing tomorrow. Thank you for all of the advice!
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Offline Deltarider

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Re: 1972 CB500 Air Pockets in Fuel Lines
« Reply #7 on: September 15, 2013, 11:33:47 PM »
It helps when fuel lines are cut to the original length. Sometimes (not always) the Parts List gives a clue. You don't mention what bike you have. For a CB 500 standard length for the two fuel lines is 18 and 30 cm (old style fuel cock) or 17 and 28 (new style fuel cock). Avoid the use of inline fuel filters.
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