WTF? What am I doing wrong? - Harley Davidson Forums: Harley Davidson Motorcycle Forum
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post #1 of 34 (permalink) Old 01-02-2017, 03:57 PM Thread Starter
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Gas tank overflow!

I have a Fat Bob split tank setup.

The trouble I am having is when I need to fill with gas. I fill the right tank and never open the left tank. But for some reason the left tank overflows every time. Gas begins seeping out of left gas cap rim. Not just a little, but a lot.
If I level the bike and look in both tanks, the left tank is always a touch higher and not level. Of course when I lean it back on the stand, gravity takes over and the angle of the bike forces gas to over flow out left cap.

If I siphon gas from left tank while bike is off stand and level, the left tank bubbles and seems to vacuum suck gas into the left tank. I siphoned gas about 2 liters from left tank to a point where I could put it in the stand and it not leak.

It appears both caps are vented. This might be part of the problem.

Last edited by Themike13; 01-04-2017 at 12:26 PM.
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post #2 of 34 (permalink) Old 01-02-2017, 04:17 PM
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Plug the left hand tank port with a fuel gauge.
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post #3 of 34 (permalink) Old 01-02-2017, 04:19 PM
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Please introduce yourself in the New to community forum. We want to know where you're from? Pics are nice. And if you're going to stick around.
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post #4 of 34 (permalink) Old 01-02-2017, 04:28 PM Thread Starter
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Intro was the first thing I did before posting this. Thanks.
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post #5 of 34 (permalink) Old 01-02-2017, 04:38 PM
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Don't want to sound like a smart a** but have you tried filling from the left tank first? Either way, it does sound odd that the gas overflows so much coming from the right. bbally's suggestion sounds like a good one
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post #6 of 34 (permalink) Old 01-02-2017, 04:40 PM
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you do understand how gravity works I hope..... the gas flows to the carb because the gas caps are vented

put a piece of wood under the kickstand to raise the bike up a bit. There is also a kickstand wedge that can be installed if your bike leans too much
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post #7 of 34 (permalink) Old 01-02-2017, 04:41 PM
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to me it sounds like a better seal is in order....but I just throwing darts in the dark...

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post #8 of 34 (permalink) Old 01-02-2017, 04:43 PM
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How's the gasket around cap?
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post #9 of 34 (permalink) Old 01-02-2017, 04:54 PM
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Quote:
Originally Posted by misinlink View Post
to me it sounds like a better seal is in order....but I just throwing darts in the dark...
Quote:
Originally Posted by FritzHD View Post
How's the gasket around cap?
My son's Fat Boy has dual tanks. He always fills the left tank first, caps it, and then fills the right tank. The left cap seal should not leak, so the gasket does appear to be defective. One other thing--far-fetched, maybe, but possible--a bad crossover hose with a bubble on the inside acting like a one-way valve. Check this by holding the bike vertical while up through the left filler neck and looking into the right filler neck to see if both tank levels rise at the same rate. Yeah, I know it sounds weird but I've seen this happen with old brake hoses. But I really think a new gasket on your left cap will get you straight.

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post #10 of 34 (permalink) Old 01-02-2017, 04:57 PM Thread Starter
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Please introduce yourself in the New to community forum. We want to know where you're from? Pics are nice. And if you're going to stick around.
Intro was the first thing I did before posting this. Thanks.
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