Hot Rods Air bubble in fuel line

I am having a problem with my 57 Chevy. The truck is hesitating and running like shit when I drive it. It seems to be getting worse. When I get out and check the engine there are air bubbles in in the glass fuel filter when I rev the engine. I have an Edelbrock carb and it has been running fine.. just recently stared to sputter and stall sporadically. I changed the spark plugs and still having the issue. When I turn the engine off and let it sit it runs fine until I start driving again.

 

Air leak in fuel line from pump to tank...could be rusted line, bad or loose fitting, rubber flex line shot. Everything behind the pump is under suction...a tiny leak pulls in bubble, anything above tiny will leave you walking.

 

Yes, replace the rubber line out of the bottom of the tank, often neglected on those trucks.

 

See how it runs with the gas cap off

 

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Mechanical fuel pumps do not like being asked to move air. They are much happier with and uninterrupted source of liquid. As noted you likely have a suction side sir leak. Just went through it with a friend who recently replaced the flex hose between the frame and the pump. Car wouldn't run at all with any kind of a load. Noticed that the intake side of the pump was damp with gas. Tightened the fitting, problem solved.

 

Replace the fuel line - petrol containing ethanol eats away at rubber hose and makes it porous.

 

Ethanol is a bitch , the old Harley has a balance hose between tanks , I check and replace it on a two year cycle . Riding about a month ago and get the strange smell of raw fuel. WTH . I pull over sure enough , split hose . Luckily enough I was able to drain on side of the tank and plug the hose on the Petcock side and crawl home . Replaced it with Silicone hose , will see how this does . Silicone I found has no string reinforcement . Hose manufactures need to upgrade to stop ethanol from ingesting fuel hose

 

bruce hit the nail on the head , also sometimes the line looks solid but the rust has pin holes in it and it will vapor off instead of leaving a damp surface . they do sell a dye you can put in the fuel and hit with a UV light to show where the leak is at . and if you have old rubber hoses go with new Viton fuel injection hose as it can handle alcohol and other octane additives NOT Buna N .

 

There is a small rubber line out of the tank sender to the steel line that runs to the pump (if it is original). The first time I touched mine it disintegrated. I got a new one for $7. Might consider running new lines tank to carb like others have suggested. You can get copper/nickel lines from AZ for $25 and flare your own. I had an easier time with those than the green coated steel lines.

 

I once had a small block powered chevy truck that had the original rubber line from the steel line to the pump. It would run fine when not under load and fall flat on its face when it was under load. We fought it for 3 days then I finally pulled it up against a tree and had my buddy feed it in gear, not enough to spin the tires but enough to load it up, I looked down for some reason just in time to see the rubber line collapsing on itself. Changed the line and it ran fine. It was collapsing where the line bent to make it from the steel line to the pump.

Bubbles can come from any number of sources like bruce mentioned anything on the suction side of the pump.

 

Well…. I replaced all of the fuel lines and the fuel pump. I started out this morning and the truck ran fine for awhile. Once it got hot the hesitation started again. It seems like it's worse when I am on the gas and then I turn it off for a few minutes and then it revs fine until I get on the road and drive for a little while. Im pissed. Is there a chance this is a carb adjustment or choke issue?

 

Are there still bubbles?
You need to figgerout first whether this is a fuel issue. Driveit until the trouble is getting bad, then choke it some...put in a temporary wire to pull choke, if it has automatic choke. If it's actually running out of fuel feed, choking will very briefly yank in more fuel from the bottom of the bowl and give it a very short burst of power.
If nothing...the going to pieces when hot is typical of coils and condensers on their last legs. Trw swapping those for whatever you have in the garage.

 

If you still have the air bubbles after changing all the lines, check the fuel pickup in the tank. I've seen them with rust holes in the tube.

 

Float level correct?

 

I personally had this problem with my '62. My gas cap wasn't ventilated. It created a vacuum in my gas tank and made a big "FOOOOMM" when I took the cap off. Ripped some holes in the gasket on the cap and it worked fine

 

This piece of gas line drove me crazy,the fuel pump gas sucking as much air as gas and the car ran horrible.

The ethanol in today's gas deteriorates the rubber line and results in cracking..


Check the simple things first. HRP

 

Maybe you're fuel is boiling? If running without a gas cap to test fails, try sleeving the fuel line out of the pump. Wrap some bounty then aluminum foil. If that helps then try this stuff as a permanent fix:

http://www.amazon.com/gp/aw/d/B0002...eat+shield&dpPl=1&dpID=31bnBSstOfL&ref=plSrch

Worked like a charm for me.

 

Yep, I used to have this problem with my 59 Vette. The fuel line got hot at one point and created vapor lock. Made a little heat shield and problem solved. Tested it first with aluminum foil, as shown above.

 

Sorry this thread wont go away :/ …. I replaced all of the fuel lines, took the carb apart and cleaned it up and added a glass fuel filter to the fuel line coming out of the tank. Got in and drove it for mostr of the day with no issues….. THEN once I got on the highway and drove about 10 minutes the hesitation started again. The truck never stalled but there was no power and it sounded like it was gulping for air/gas… I pulled over and opened the hood and Im still getting the bubbles in the glass filter near the carb but not the one behind the seat. There was some shit in the filter behind the seat so a new fuel tank is on my shopping list this weekend. I limped the truck home and when I got home and turned off the truck I was getting a fizzing/bubbling in the glass filter near the carb with the engine off. Not sure if the is a suction effect or if this is boiling fuel from heat. ?? There is a large vacuum hose that comes out of the plate under the carb and plugs into a sensor or something on top of the block. YEsterday I noticed when I revved the engine it was collapsing. I unhooked it and the engine died so I plugged it back in. Today I would almost swear that when I revved the engine the hose would swell and semi collapse when I let off the gas. Pretty much the opposite of what it was doing yesterday. Is my '57 Chevy truck possessed or just fucking with me?

 

That looks like a PCV valve, put a new hose on it and see if it helps.

 

Is it possible that the rubber diaphragm in the fuel pump is split, or sagging from E85? Or if your pump has the little reed valves stuck or cracked. What about a fuel pressure gauge to check the system?

 

Have you tried making a heat shield or insulating the line yet?

 

Your pcv may have gotten clogged but that shouldn't cause fuel issues. It might cause vacuum issues and possibly cause your valve covers to weep. You can get a new one for less than $5.

Do you have vents in your valve covers? You don't need them but they may be helping the situation if you do.

I had one issue after another with my truck but it was sitting for a long time before I got it. Once I replaced all the usual stuff the small issues went away.

 

I went and bought some heat sleeves this evening and wrapped the fuel line running from the fuel pump top the carb and the fuel line that runs under the truck near the exhaust. I'm looking forward to running it tomorrow and seeing if that made a difference. I am trying to be optimistic. That was really weird seeing the fuel line fizzing and bubbling after the truck was turned off today. I have never seen that before.

 

All of this and no mention of you running without the gas cap to see if it's not venting. Everything off and you still see shit happening, like maybe pressure/vacuum in the system because the cap isn't venting?

 

and if I may, I'd replace the collapsing hose. and is the PCV seated in the grommet?

 

A trick I learned from a diesel mechanic [ and me playing with diesels ] is to have a piece of clear plastic fuel line as a diagnostic tool.
You put it inline , and one by one chase the air leak backwards towards the tank until the bubbles disappear.
It can sometimes be something as simple as a hose clamp

 

Yes dude I ran the truck without the gas cap. That was the first thing I tried. Thanks!

 

I tried to seat the PCV but it wouldn't seat.. it just wobbles around. I will get a new one and hose. Thanks