1966 Mustang Bubbles in the Fuel Filter - Ford Mustang Forum
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post #1 of 13 (permalink) Old 11-28-2019 Thread Starter
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1966 Mustang Bubbles in the Fuel Filter

1966 Mustang with a 289, 3 speed, I am getting bubbles coming into the fuel filter from the inlet side after it warms up. I have changed the fuel pump, but the problem continues. I have inspected the entire fuel line and hoses for damage, none.



The entire fuel system from gas cap to carburetor was installed new about 6 years ago during the car rebuild, and has not had a problem before this started a few weeks ago. So I do not think it is a fuel boiling issue. No leaks noted anywhere. A half tank of gas, so should not be sucking air at the pick up.



The only thing left I can think of is to change the plastic fuel filter which has been on there about a year.


1968, hardtop, 289, C4, seafoam green.
1966, hardtop, 289, original 3 speed, on the road and fun to drive.
1968, hardtop, 200, 3 speed, in work.
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post #2 of 13 (permalink) Old 11-28-2019
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The filter is between the pump and carb and you see bubbles only at the inlet side of the filter?

I doubt there is anything wrong. If you were sucking in air then you would also likely be leaking out fuel when its not running. Its just winter fuel trying to boil. It was 80F yesterday in Panama City which is pretty warm for 'winter' fuel to not bubble a little in a warmed up car. Many of us who are now at 30F aren't seeing those bubbles.

Pressure on the fuel suppresses bubbles, vacuum makes them more likely. A factory mechanical pump applies vacuum to the fuel line to suck the fuel out of the tank so a few bubbles now and then wouldn't surprise me. As long as the bowl in the carb stays full no one cares about bubbles. If you take the top off the carb in the summertime you will see bubbles in the float bowl.

Changing the filter should not be expensive but I doubt it will change anything.

Ford used metal filters so no one could see any bubbles. :-)

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post #3 of 13 (permalink) Old 11-28-2019
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The bubbles are normal, move on to something else to fix.

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post #4 of 13 (permalink) Old 11-28-2019
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As already said, it is normal and won't affect the engine at all.
If it annoys you, buy a filter that you can't see through.

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post #5 of 13 (permalink) Old 11-28-2019
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Must be from that detergent gasoline.

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post #6 of 13 (permalink) Old 11-28-2019
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Right, Yadkin! Scrubbing bubbles! Even better in your fuel than in your bathtub!
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post #7 of 13 (permalink) Old 11-29-2019 Thread Starter
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After I posted this I realized I should have also included the very first symptom which was the engine would stop as I was driving down the road. Happened maybe 8 times in a 10 mile drive to the post office. Seemed the carb would empty, engine stop, I would coast, pull over, wait maybe 30 seconds and it would start up after some cranking. Drive about a mile and the whole thing repeat. Not the best way to limp home. Got it to repeat at home. So that is when I got concerned about the bubbles causing the starvation. I have never noticed them before all this started.



I have not had a chance to test drive it around the neighborhood. So I shall see how that goes soon. These are the answers I was hoping for. Thanks.



But it feels good to work on the car after a year of hurricane recovery. And thankful my cars did not get damaged.
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1968, hardtop, 289, C4, seafoam green.
1966, hardtop, 289, original 3 speed, on the road and fun to drive.
1968, hardtop, 200, 3 speed, in work.
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post #8 of 13 (permalink) Old 11-29-2019
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With a carb, so long as there's fuel in the bowls, you could practically squirt foam down the line to the carb and still have your engine run smoothly.


Usually, for a hard intermittent stall without any other symptoms (no stumbling or rough running, happens during cruise) you need to look at electrical. Maybe your coil's going out, or a wire in your ignition is loose? If the car stumbles before dying, that could indicate the fuel bowls running dry, but that's kind of a weird problem since you have a new fuel pump and you can see your filter. Is it possible that you've got a second filter in your system that's clogged? Or perhaps your fuel pickup in the tank is all rotted? If it's rusted through, that could explain picking up some air. However, unless it's clogged the fuel line with rust and crud, even a 'lot of bubbles' in your fuel delivery would not cause your carb any trouble.

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post #9 of 13 (permalink) Old 11-29-2019
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Quote:
Originally Posted by Driveway View Post
After I posted this I realized I should have also included the very first symptom which was the engine would stop as I was driving down the road. Happened maybe 8 times in a 10 mile drive to the post office. Seemed the carb would empty, engine stop, I would coast, pull over, wait maybe 30 seconds and it would start up after some cranking. Drive about a mile and the whole thing repeat. Not the best way to limp home. Got it to repeat at home. So that is when I got concerned about the bubbles causing the starvation. I have never noticed them before all this started.



I have not had a chance to test drive it around the neighborhood. So I shall see how that goes soon. These are the answers I was hoping for. Thanks.



But it feels good to work on the car after a year of hurricane recovery. And thankful my cars did not get damaged.
I'm thinking that you are getting air in the fuel line ahead of the pump. Since that portion is under vacuum, it could be drawing air in through a leak in a joint or connection.

You stated that your six year old fuel line had no damage. Re-inspect and tighten the fittings and make sure that they are tight. Air is getting in somewhere.

The other thing you should do is replace the plastic fuel filter with a larger metal one, like a Fram G15. Plastic can crack and squirt fuel on a hot engine (never a good thing). It should be downstream of the pump so it's under pressure. Mount it so the outlet is below the volume of the cylinder. The larger volume should help to consolidate bubbles.

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post #10 of 13 (permalink) Old 11-30-2019 Thread Starter
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Thanks for the input. The big delay in a test drive has been trouble getting the u-joints changed out. Got a new one with a scored post and took 3 days to get a replacement due to the weekend. Then the Thursday and Friday thing with the wife.


Thanks for the suggestions. I'll let you know the results.

1968, hardtop, 289, C4, seafoam green.
1966, hardtop, 289, original 3 speed, on the road and fun to drive.
1968, hardtop, 200, 3 speed, in work.
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Quote:
Originally Posted by Grimbrand View Post
Usually, for a hard intermittent stall without any other symptoms (no stumbling or rough running, happens during cruise) ...
...If the car stumbles before dying, that could indicate the fuel bowls running dry, but that's kind of a weird problem since you have a new fuel pump and you can see your filter. Is it possible that you've got a second filter in your system that's clogged?
...Or perhaps your fuel pickup in the tank is all rotted? If it's rusted through, that could explain picking up some air. However, unless it's clogged the fuel line with rust and crud, even a 'lot of bubbles' in your fuel delivery would not cause your carb any trouble.
My money's with junk/rust in your fuel tank. As the engine runs, the rust particulate will be sucked up into a filter or around the fuel intake in the tank (especially if there is a sock or screen around the intake, eventually clogging enough to stop adequate fuel delivery.

It also accounts for the bubbles -- the vacuum is having to suck harder and harder and will make bubbles when it pulls too hard.

When the engine stops and the vacuum ends, the particles fall back away from clogging the lines; when you re-start the car, you'll be able to drive a short distance until the filter or intake get re-clogged.

I had this happen to me with several of my old cars. In fact, this happened to an old Jag when I was about 20 miles from home. Every time I was ready to call a tow truck, the car would start back up and i could drive a short distance.

With each re-start, the car progressively travelled less and less distance.
Sounds exactly as you described.

Pulled the tank and acid washed it and coated the insides with RedKote -- believe it or not, it's a very easy DIY job for about $100 over 2 days (have to pause between steps)(I can describe how to do it if you find it cheaper than buying a new tank).
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If the engine hard stalls, pull your air cleaner, look down into the carb and operate your throttle to see if there are 2 solid streams of fuel squirting down into the manifold. Most vacuum gauges second as fuel pressure gauges. Hook one up to your fuel line, disconnect your coil center post wire and crank the engine. You should have around 6#'s of fuel pressure.

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I'd take a look at that "installed new" gas cap.



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