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Air in fuel line only when pressure fitting is connected?

Old 07-25-2007, 07:08 PM
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webdr
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Default Air in fuel line only when pressure fitting is connected?

Im breaking in my boat and Im seeing extreme bubbles from the tank to the carb, causing all that erradic BS.
When I unplug the pressure hose, its solid fuel. I have a new tank in route but what else could cause it?
Im not seeing any fuel leaks and the tube from the tank to the carb doesnt appear to have any nicks. I can see the bubbles originating from where the tank and tube meet.
Any advise?
Old 07-25-2007, 07:24 PM
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dicko
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Default RE: Air in fuel line only when pressure fitting is off?

replace the fuel line, often you can get minute cracks that you can't see which will leak air.
Old 07-25-2007, 07:42 PM
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gooycheese
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Default RE: Air in fuel line only when pressure fitting is off?

If you are running a proboat ? Make sure the nipple on the tuned pipe isn't loose, that will cause big problems if it is. If you wanted tank the tank out with both the hose going to the carb and the hose going to the pipe and hold the tank under water and blow thru one end and hold the other end closed, if you see bubbles you know where your leak is. Make sure your fuel cap is tight when you put it under water.


Paul

I have TC31 and the pressure nipple on the pipe was a pain it would always come loose on me.
Old 07-25-2007, 11:29 PM
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Default RE: Air in fuel line only when pressure fitting is off?

Make sure the cap is on tight, you don't have any pinholes and your tubing is the right diameter. If those aren't the problem, try zip tying the tube to the nipple to create a better seal. Other than that I have no idea...
Old 07-26-2007, 06:31 AM
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Sean Bowf
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Default RE: Air in fuel line only when pressure fitting is off?

Not quite sure what you are saying.

The title to your post says you get air in the fuel line when the pressure fitting is off (disconnected). I think that might be somewhat normal. The pressure in the tank helps reducing foaming of the fuel while the engine is running. So, if it looks correct when the pressure line is connected to the tuned pipe, then who cares what is looks like when it is disconnected. You arent supposed to run it without it being connected.

In your post you said that if you unplug the pressure line you get solid fuel. This sounds the opposite of the title. This sounds like if you disconnect the pressure line from the pipe, all the bubbles go away. If this is what you are saying, then all the advice given above applies. If you are saying you actually plugged the pressure line with something with it disconnected, and got the bubbles...again, this is not how you are supposed to run the engine... But if you are trying to run it this way (with the pressure line plugged), the fuel tank has to take in air to replace the fuel that it is using, and you might actually have a small air leak where the line hit the tank, since you said that you see the air originate from this location.

Sean
Old 07-26-2007, 08:40 AM
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webdr
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Default RE: Air in fuel line only when pressure fitting is off?

yea, I goofd on the title and I corrected it, I get air in the line when the pressure hose is connected, I disconect it from the header and the fuel goes solid through the line.
Old 07-26-2007, 10:08 AM
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Default RE: Air in fuel line only when pressure fitting is connected?

The pressure line should go to the top of the tank and the fuel supply should come from the bottom of the tank. If the pressure line is immersed in the fuel it will cause bubbles in the fuel that may be picked up in the fuel supply to the carb.
Old 07-27-2007, 05:57 AM
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Default RE: Air in fuel line only when pressure fitting is connected?

I think there is a crack in the bottom of the tank. I have not pulled it out cause it takes a bit of work and Im heading out of town for the weekend.

I filled it with fuel and ran most of it through for the breakin. I left about 1/4 of a tank in there and within a few hours, all the fuel was in the bottom of the boat! Lame...
Old 07-27-2007, 10:12 AM
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Default RE: Air in fuel line only when pressure fitting is connected?

Either that or your connection is loose. One thing you could try is using cable ties (aka tie wraps or zip ties) to fasten the tube to the tank. Make sure that the cable tie sits behind the ridge on the nipple or it'll slip off. If that doesn't work, you might as well take out your tank. Get a container that the tank will fit in, fill it with water. Then take the tank, plug off one end and connect an airhose to the other end. Put about 2 psi into it. If bubbles come up, you have a leak. If it leaks, congratulations, your tank is out and ready to be swapped. If it doesn't leak....I have no idea whats wrong...
Old 07-27-2007, 11:28 AM
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Default RE: Air in fuel line only when pressure fitting is connected?


ORIGINAL: webdr

I think there is a crack in the bottom of the tank. I have not pulled it out cause it takes a bit of work and Im heading out of town for the weekend.

I filled it with fuel and ran most of it through for the breakin. I left about 1/4 of a tank in there and within a few hours, all the fuel was in the bottom of the boat! Lame...
One of the things I do with a new tank, or a second hand one that I pick up, is to pressure test it. Put fuel tubing on one or both of the tank lines. Plug one and blow into the other to pressurize it. Pinch off the one that you've blown into and hold it for a few seconds. When you release it, a bit of air should come out.
Old 07-27-2007, 09:06 PM
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Default RE: Air in fuel line only when pressure fitting is connected?

This scenerio doesn't make sense. If the fuel system is presurized, the fuel would be forced out of the crack in the tank. It would not pull air in. Even if the fuel lines were leaking, the fuel would still be pushed out by the pressure. Is your pressure plumbing at the top of the tank and your pickup for the carb at the bottom (preferably at the bottom left side, assuming you are making the typical right turns)?
Old 07-28-2007, 06:48 PM
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Default RE: Air in fuel line only when pressure fitting is connected?

Another thought --- Are you sure your "pressure" line is providing pressure and it's not installed such that it is sucking out of the tank. With a cracked tank or a leaking fuel supply line that would suck air into the tank or fuel line and cause the bubbles. That's the only scenerio that make sense to me.
Old 07-29-2007, 05:57 AM
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Default RE: Air in fuel line only when pressure fitting is connected?

if there's a crack in the tank, the tank will leak air (if above the fuel line, ie leaking from the pressure nipple or filler cap). Under pressure a leak will create uneven pressure on the fuel distribution into the carby creating a lean mixture, especially under acceleration & top speed. You can't get the pressure line to suck, the fuel line sucks, the pressure line comes off the exhaust (which is under pressure) and into the tank, this puts pressure onto the tank & helps to reduce the affect of the tank draining fuel. as the fuel in the tank drains down it has less weight of fuel above the fuel nipple & the fuel doesn't flow as freely to the carb. putting a pressure line onto the fuel tank from the exhaust pipe pressurises the tank so that under low fuel volume, fuel will still flow down the fuel line into the carb. if there's a leak in the tank, the pressure is reduced and the engine won't get enough fuel (run lean). if you have a crack in the fuel line, under accdeleration, it will suck fuel down the line & air will come in through the crack from the ventury affect. this will also lean out the mixture and cause eratic tuning.
Old 07-30-2007, 07:49 AM
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Default RE: Air in fuel line only when pressure fitting is connected?


ORIGINAL: John Palica

Another thought --- Are you sure your "pressure" line is providing pressure and it's not installed such that it is sucking out of the tank. With a cracked tank or a leaking fuel supply line that would suck air into the tank or fuel line and cause the bubbles. That's the only scenerio that make sense to me.
I put my finger over the pressure nipple and I cant even feel any exhause coming out of it. I pit a needle in there to see if it was clogged and its open. Why would it not be pushing pressure? Im going to take it off after work today as well as pull the tank.

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