Strange phenomenon - bubble in gas line?

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Model T Ford Forum: Forum 2017: Strange phenomenon - bubble in gas line?
Top of pagePrevious messageNext messageBottom of page Link to this message  By Peter Adey (The Woodlands TX) on Saturday, April 15, 2017 - 04:26 pm:

I have had a lot of fuel line issues of late. I removed the modern paper/glass inline filter and replaced it with he proper sediment bulb and rerouted it further away from the exhaust. After that she ran a few miles and just died. I bled the line at the carb and was off again - all was fine for weeks and many miles. A small leak then occurred at the line into the carb and I promptly took care of that. Once again hit the road and in a few miles died again! Bled the line and all seems fine now. Is this a common problem - when messing with the fuel line air must get in and when the bubble gets to the carb it dies? OR is this a sign of a bigger problem? Inquiring mind wants to know!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Verne Shirk on Saturday, April 15, 2017 - 05:05 pm:

Could be more crud in the line plugging the screen in the sediment bulb. Could also be vapor lock from alcohol fuel which vaporizes quicker than pure gas. Several of us guys around here are running pure gas from Quick Trip.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Susanne on Saturday, April 15, 2017 - 05:07 pm:

I would pull your carb, and find out why that bubble is causing your needle valve to close... and remain stuck. Your symptoms are NOT normal, and while you may think it's the fuel line, you have enough fuel in your normal carb bowl to run for at least a minute or 3... and by then your float should drop and allow a FREE FLOW of fuel to the bowl until full...

I am not a fan of the paper filters (had one disintegrate on me, causing no end of grief to a winfireld I ran) so you may have paper debris jamming your needle travel... also what year car, carb, and if not stock, what kind of carb? a NH will act differently than, say, a zenith aftermarket or a 4 ball...

But, yeah, I would look at why your carb bowl is draining and staying that way. For me the easiest is to pull the carb, the bowl, and check the pivot pin for galling or gunk (varnishy or that goopy crud from modern fuel) keeping the bowl from dropping or the needle from opening... Then once I knew all that was jake, I'd start digging - Clogged fuel line (you ran the wire thru it, yes?). crud in the gas tank, etc...

Also make sure your newly fuel line is away from anything exhaust - I have mine against the outer frame rail to keep it as far from that hot hot pipe as possible.

Good luck (and happy Easter!!!)

:-) Susanne


Top of pagePrevious messageNext messageBottom of page Link to this message  By Peter Adey (The Woodlands TX) on Saturday, April 15, 2017 - 05:24 pm:

It is an NH carb - When I fixed the leak in the line I did pull the carb and the action on the needle looked fine and it was very clean.. It has one of those neoprene tips.. The line flows well and fast so I am stumped. This seems to only happen every time i mess with the line - then after the one stall - she seems fine. But i sure hate those stalls! Fortunately each time I have had enough momentum to get off the road.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Semprez-Templeton, CA on Saturday, April 15, 2017 - 05:33 pm:

Sounds like classic vapor lock to me. When gasoline boils a bubble of gasoline vapor forms stopping the flow of liquid fuel. This phenomenon is usually caused by the fuel line being located too close to the hot exhaust pipe.


Top of pagePrevious messageNext messageBottom of page Link to this message  By gary hammond-Forest, Va on Saturday, April 15, 2017 - 05:40 pm:

Make sure your fuel cap vent doesn't have a spider, etc blocking the vent


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Saturday, April 15, 2017 - 06:10 pm:

The fuel line must not have a high point in the middle. It must run uphill at each end. That way the fuel will flow either toward the tank or the carburetor. Air compresses and will be caught in any high point between the two ends. That will prevent fuel from flowing. It just compresses the air. So check the routing of the line.

Beside air in the line, water will also cause the engine to stop. Any water which is in the gas tank will go to the bottom and flow into the line and into the carb. This problem can be remedied by opening the valve at the bottom of the carburetor and letting the water drain out. Also the drain at the sediment bulb open will drain out water from the tank.

Another cause might be vacuum. This is caused by a plugged air vent in the gas cap preventing air from entering the tank to replace the space occupied by the gas as the fuel leaves the tank. When enough vacuum occurs in the tank it will prevent the fuel from flowing.

Two other potential causes would be the float or the needle sticking in the closed position or dirt clogging either the input needle or the high speed jet in the carburetor.

On the earlier cars (before 1926-1927) another condition is lack of pressure caused by low fuel level. If the car runs fine with a full tank but when it gets down below 3 gallons it stops running, you have low pressure problem. Any air bubble or any of the other above listed causes will be worsened by low pressure.
Norm


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