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Author Topic: Fuel Line Problem  (Read 1519 times)

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Offline mkramer1121

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Fuel Line Problem
« on: June 25, 2006, 09:14:42 AM »
Ok, well, long story short, the petcock on my bike (CB550) is NOT original, 2 owners ago the tank was going to be used for a chopper build, and the hole for the petcock was drilled out.  So yeah, I've got a homemade petcock/fuel line, basically a brass valve (turn style open) to a plastic fitting to a fuel filter to the line to a T fitting.  The problem I've had lately is I have been getting air bubbles in my gas line, thus killing the bike.  The only way to get these trapped bubbles out is to turn off the petcock, remove the fuel filter and line, open the gas cap, start slowly trickling gas into the fuel filter to force any air out, then open up the petcock full force and reattach the filter to the petcock.  And the bike runs fine until the next time.  Now, what I may be thinking it is that I haven't been turning off my petcock when I park the bike at night, and I really notice the air bubbles in the morning.  Could this be the problem?  Otherwise I'm stumped, and will be looking for a new tank and original petcock to fix the problem.
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Offline TwoTired

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Re: Fuel Line Problem
« Reply #1 on: June 25, 2006, 10:34:18 AM »
Gravity feed fuel systems need a constant fall or slope between source and destination.  Or, as you've found out, air bubbles will collect at the high points.  Side stand parking probably makes your routing worse in that respect.

The original routing was fairly short and to the point.  The fuel tank was pretty much the high point even on the side stand.

I suggest you re-engineer your routing so that there is constant slope or fall for the fuel beteen tank outlet and carb input.  The fuel "tees" at the carbs should face upwards, too, or directly to the holes in the carb mount flange.

Cheers,
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Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline merc2dogs

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Re: Fuel Line Problem
« Reply #2 on: June 25, 2006, 12:57:24 PM »

 Now I've always pointed the tees down, then ran the hose under the carbs for the same reason, the lowest spot is the bottom of the loop, and both ends are high, any bubbles will run into the carb or back to the tank, have only seen bubbles at the carb side once, and any bubbles I see dissappear as soon as I turn the fuel on.  highest point at all lean angles is the tank, second highest is the carbs.
 
The only fuel issues I've ever had with that bike is the  #$*@# kreem sealer that some moron (^$#@ put in the tank without proper prep.

Ken.
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Offline Gordon

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Re: Fuel Line Problem
« Reply #3 on: June 25, 2006, 01:10:11 PM »
Yep, a downward bend in the fuel line is fine, it's the upward bends that will cause you problems. 
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Offline TwoTired

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Re: Fuel Line Problem
« Reply #4 on: June 25, 2006, 01:20:50 PM »
How's this for an armchair analysis...

Pointing the tee's down ought to work for a daily driver.

Consider a bike infrequently driven, and the fuel petcock turned off while being stored.
The gas in the carb bowl evaporates, the floats and float valve drop until the line loop gas level is lower than the float valve level. Continued evaporation then glues the float valves and possibly the float pivot in their lowered, open, positions.  When the gas is turned on next, the carbs overflow.

Admittedly, this can happen to the stock routing and set up, too.  However, the entire gas supply in the fuel line must drain into the bowls before this can happen.

Also, an air pocket at the closed float valve entrance, with full fuel bowls, could possibly glue the float valve shut.  Again with periods of diuse.

Food for thought...

Cheers,


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Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline Gordon

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Re: Fuel Line Problem
« Reply #5 on: June 25, 2006, 01:32:57 PM »
Quote from: TwoTired on June 25, 2006, 01:20:50 PM
How's this for an armchair analysis...

Quality!
But the best solution to that is ride the bike more often!! ;D
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Offline merc2dogs

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Re: Fuel Line Problem
« Reply #6 on: June 25, 2006, 02:00:20 PM »

 as I ride my bike regularly I'd say that's why I've never had that problem,  now all I have to figure out is why it doesn't happen when I get it out of the garage in the spring!
  I don't think the amount of fuel in the lines would add very much at all to the time it would take to drain the bowls 1/4" line x 6" long?

 Though if you wanted to go that route, you'd still have the same head from tank to carb inlet that would flow into the carb so unless the line was routed straight down under the carbs, then to the carb you would have the same volume of 'reserve' fuel filling the bowl as it evaporated so you'd have the same time before stiction.

 no affront intended you just posed a question that was interesing and that's what I came up with.

ken.
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Offline mkramer1121

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Re: Fuel Line Problem
« Reply #7 on: June 25, 2006, 05:25:59 PM »
Thank TwoTired, I appreciate your help as always.  I'll see if  can find a straight down routing from the tank.
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