air bubbles blowing in fuel bowl

34flathead

34flathead

Senior Member
hi, has anyone seen or noticed air bubbles blowing in the glass fuel bowl when the motor is just idling? (blowing in every 3 or 4 seconds)
did you figure out what was causing it?
this is happening in a '48 merc.
rich
 
Rich, You apparently have a compromised fuel line that allows the intake of air. You're lucky you have the glass bowl to detect the problem before it stalls you on the side of the road.

Most common causes are a pin hole in the flex line, a glass bowl cork leak, or a loose clamp on an inline fuel filter. Also check and tighten all other fittings from tank to fuel pump.

Edit:
Rich, as reported by GM in another post, you may have fuel actually boiling in your glass filter bowl. The Ehanol/Gasoline fuel we get these days is highly volatile and causes these problems.
 
Last edited:
it usually will be hard or won't start if the fuel pump is sucking air. Is this when it has been run a while and the engine is hot? If so check check the temperature of the pump and the thumb screw under the glass bowl. The bubbles start in the 120 to 125 temperature of these parts and get larger as the heat gets hotter. Read the detailed post I just posted. G.M.
 
Get a new cork gasket for under the glass bowl [its the cheapest way to eliminate that problem if thats what it is.] Do not use a rubber one. I'll send you a couple if you cant get the correct size. There are several diff ones must be the correct one.Need address to mail n/c ken ct. email me if you want them. igadore@sbcglobal
 
thanks guys, i will tell them to get the gasket changed to cork, as it is a rubber gasket.
the car starts but has very low spark at times as checked with the spark tester, the one you plug into the plug wire and on top of the spark plug.
the air comes shooting down as from the fuel line coming into the top of the bowl, i will take my camera over tomorrow and try and film it.
rich
 
You defininatly leaking air from the top through the rubber gasket.Why do people insist on using this crap they dont hold up to this corn gas. Make sure the cork fits the housing good.The screen goes on first then the gasket.Not the other way around ken ct. New screens are availible. ken ct.
 
I put on a new Airtex pump 4 years ago the pump still works perfect. I have a gauge installed in the line from the pump to the carb and can see the steady pressure it provides as long as the fuel doesn't get over 125 degrees. I had the glass bowl off 2 days ago to change the filter and the rubber is still in good shape after at least 6,000 miles. G.M.
 
I had the same problem with my 50 I would go for a drive and it would stall half way around block. I noticed bubbles in bowl turned out it was a l line that was just clamped on got stock fuel line and no problems.
 
Re: air bubbles blowing in fuel bowl "update"

ran a gas hose from a 1 gal gas can to the fuel pump, fired it up and :D no bubbles.
need to check the inline fuel filter, that i forgot to mention, but thanks ford38v8.
when you f-up no one forgets, when you do right no one remembers. im making a note of this one.
rich
 
Rich, thanx for the update and the praise. If it's the fuel filter, you may find that you used the spring steel clamps that are always supplied with fuel filters for some reason. Toss them out and use the worm screw type of clamps.
 
One thing I might mention with all of these air in the glass bowl problems. If the air is comming from the top of the bowl it's the gasket, flex hose or fuel line Bob Shewmans flex hose will fix the flex hose problem for as long as you own the car. It's also possible to suck air down through the gas in the tank if the tank is low on gas and the pick up tube slightly closed off with debree. If the bubbles are comming from the bottom of the glass the thumb nut at the bottom and the wire bail is over 125 degrees, Bubbles from the bottom don't come from the top. Engines with cranshaft fans are going to notice the problems before generator or belt driven fans, they will get hotter in the rear of the engine as there is no air circulation. Lets get some temperature of the firewall at the fuel line clamp, pump and carb below the fuel line. The more input info provided the better the solutions can be found. G.M.
 
That rubber gasket is probably Viton. From what I've gathered, some grades of Viton hold up to ethanol, and some don't.
 
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