Gas smell when driving

[Milt K from Pa]

Hi Barners,
I have a '57 T-Bird, 312 CI, stock, with it's original Holley 4 barrel. Carb has been restored and is performing well now, after leak problems with the accelerator pump diaphram. What is happening now is a strong gas smell, but only when getting into it a bit, like when climbing a hill or a fast get-away. As long as you cruse along at a constant speed, no smell. I've checked the carb and gas lines, but no leaks. I thought about the vent hole on top of the front float chamber may spill fuel, but why only when pressing more on the pedal??

Got some ideas??
Thanks

Milt K from Pa

 

[bobss396]

I had that on my '59 Ford, it was the gas cap. This is a non-vented cap and the gasket was bad or it was a bad fit to my tank. The cap was loose and never tightened down all the way. I got a NOS cap on eBay and it fits great. See if you can pull up on your gas cap or see if gas is running down the filler neck.

 

[Ford blue blood]

Check the float level. Might be just a rch high.

 

[Johnnydidd]

Mine has gas smell if the air breather is off with breather on no smell, I cant see any gas leaks or stains anywhere, car runs great wont mess it.

 

[dmsfrr]

What is happening now is a strong gas smell, but only when getting into it a bit, like when climbing a hill or a fast get-away.

Does the car have an oem air cleaner or something else?

Possibly a bit too much fuel from the secondary side of the carburetor?
Wrong size power valves? Secondary jets too big?
Is it a Holley - List 1273 carburetor?
Holley book shows...
#85 power valve for the primaries and #105 for the secondaries
#55 primary jets and #48 secondary jets / up to 5,000 feet elevation.

.

 

[Milt K from Pa]

To all Barners
I'll try to answer all responses:
The carb is an orig 4150 Holley, list 1273, and as far as I know orig to the car. In testing, I wired the secondaries closed so I could drive without the possibility of dumping extra fuel--NO HELP, still smelled.
I have the stock '57 dry-element air cleaner installed. The specs call for a vented gas cap, which it has. I tested it and you can suck thru the vent hole bit you can't blow back through it.
I tested it today again, looking for a possible overflow from the vent in the primary float chamber. I stopped immediately upon the gas smell and checked the entire carb area, all was dry.
How can the main jets/power valves being too large allow gas odor to escape the carb since the venturi action is sucking the whole area. Is that a guess or could it actually happen.
The car runs pretty well so I hate to tear the carb down.
Still looking for the answer!!

Milt K from Pa

 

[miker98038]

"Getting into it a bit". Throttle opening, low vacumn, rpm related? I'm stumped too.

 

[dmsfrr]

How can the main jets/power valves being too large allow gas odor to escape the carb since the venturi action is sucking the whole area. Is that a guess or could it actually happen.
Milt K from Pa

Watch the 30sec YouTube video linked below.
Granted it's 2 two barrel carbs on a 4cyl engine, but you'll be surprised.

If the power valves & secondary are a bit off the fuel/air mixture can be rich but not all that noticeable since percentage wise you aren't using those parts of the carb as much.

The flow into and thru the carb isn't smooth like you'd expect, it's only sort of close.
The opening and closing of the intake valves causes pulsations in the airflow thru the carb.
This can cause a fuel/air fog or 'standoff' just above the carburetor.

Under acceleration there is even less intake manifold vacuum to draw the fuel fog into the engine.
If this fuel fog isn't contained inside the air cleaner you'll smell it.

Depending on the engine, cam specs, rpm and carbs this can be a small or large problem.
Tired intake valves could also accentuate the problem.

https://www.youtube.com/watch?v=zs8mnaouP8U

https://www.google.com/search?q=fuel+standoff&ie=utf-8&oe=utf-8


.

 

[Milt K from Pa]

dmsfrr,
Watched the video on the 4 banger you suggested and was amazed. But the difference on my 312 engine is that it is at fairley low RPM's, not even a down-shift, just give it some throttle to climb a slight hill!! I had checked compression a while ago, but in seeing a comment about intake valves not seating, could cause blow-back, could be a question. Hope maybe some one else may have a brain-storm.
Thanks to all

Milt K from Pa

 

[fordor41]

check fuel pump pressure. Too high can cause the bowls to overflow

 

[Lanny]

A gas smell don't have to come from the engine compartment.

You mention going up a hill , or stepping on the throttle a bit.
Have you checked the gas tank area, for gas slosh causing a small leak ?









.

 

[oldave57]

One thing to take a look at is the fuel tank sending unit. My 57 Fairlane 500 was having similar issues, particularly when the tank was just filled. I found that the sending unit gasket (which was a cork composition gasket) had completely dried up and also that the seal on the sending unit itself was allowing fuel to pass. I ordered a new tank seal and installed it which helped, but had to also add some silicone seal between the sending unit flange and pivot bracket which is mounted to the flange. I used Permatex "Ultra Black" silicone which I have had good luck with in similar application. Since then, no more gas smell.

The sending unit is held into the tank by a twist lock ring that can be removed by rotating about 30 degrees. I ended up making a tool using a 1.5 inch pipe coupling and grinding out to provide 4 raised points to engage the twist lock ring. I think you could remove it by tapping with a hammer and punch (carefully) to rotate the lock ring also.

Good luck,
Dave

 

[dmsfrr]

One thing to take a look at is the fuel tank sending unit.
The sending unit is held into the tank by a twist lock ring...

The '55/'57 T-Birds use a fuel sender held in with 6 small screws/bolts. It can be accessed thru the floor of the trunk.

FYI, this tank and sender are after-market replacements not oem, the originals were rusted out. Second photo is the removed oem '55 part.
.

 

[bobss396]

The sender is a good place to look. Again, when you smell it, check for gas running down the filler neck. My Ford was doing that, only at WOT and running through the gears, all the gas sloshed to the back of the tank.

 

[Alaska Jim]

A word of caution, if you use the hammer and punch method, ( I did for years as a mechanic in the automotive field ). use a Brass punch and hammer so that you do not create a spark, which could lead to a fire , or worse an explosion. even if the tank is empty , you still have fumes.

 

[Milt K from Pa]

Barners,
The gas tank sounds like a good place to look. I wanted to take the sender out anyway due to the reading being way off. I know the sender was changed to a repop before I bought the car, so it needs some "adjusting". I'll let you know after checking for a leak.
Thanks.
Milt K from Pa

 

[dmsfrr]

A gas smell don't have to come from the engine compartment.
You mention going up a hill , or stepping on the throttle a bit.
Have you checked the gas tank area, for gas slosh causing a small leak ?

'57 T-Birds have a rubber seal between the filler neck and the gas tank. It leaks when it gets old.
There's a fuel tank vent hose back there too.

Keep a fire extinguisher behind the seat.
.

 

[Milt K from Pa]

dmsfrr and others,
Sorry I haven't been texting-busy.--No leaks at sender unit or filler neck. I didn't remove the sender yet, want to finish season of driving. Contacted a local expert and will get an educated check-out soon, AFTER Hershey!! It's really funny, you don't have to raise RPM's very much to get the smell, just call for a little more fuel, to maintain speed on a grade, and you get it. Will report after fix is found--hopefully!

Milt K from Pa

 

[rick55]

Do you get the same level of smell when the fuel level is low in the tank. If yes it is probably carb related. If no it is tank or cap related. You could have a leak or damaged gasket on the fuel gauge sender.

 

[bobioknight]

Yep, my sending unit was the culprit too, the rubber O ring had corroded and allowed fuel to escape just as you described. I certainly could not fill the tank without losing 3 or so gallons onto the garage floor. $3.00 part.