Seems like too much gas smell from the carbs.

[cleandan]

Hello all you happy people (using my best Droopy voice)
I am working on a dual quad 427FE in an ERA Cobra roadster.
BJ/BK carbs with one modification being the front carb has no choke plate.

There is no gas leaking anywhere.
I have no pull over at idle in either the primary or secondary.
Throttle blades are dry at idle.
Idle screws are out 1.125 turns.
Floats are currently set with just the slightest fuel tip out with the plug removed and me rocking the car.

Yet I am getting a pretty heavy gas smell in some situations.
I have looked for ANY signs of any fuel leakage, anywhere...None.
I am looking for fuel being pushed past the needle and seat but I find no evidence of that.
But there it is, heavy, raw gas smell.

Any ideas?

Thanks in advance for any and all helpful suggestions.

[thatdarncat]

Do you have original Ford BJ/BK Holleys, or reproductions? I don’t know for sure about the reproductions, but the original BJ/BK’s had bowl vents on the primary & secondary float bowls that are open to the atmosphere, along with the regular vent tubes Holleys have that are inside the air filter area. And you probably have open element air filters? That could be allowing more “smell”. What are you running for fuel? Pump gas with ethanol? Ethanol has a much lower boiling temperature, it could be vaporizing in the float bowls and with the extra bowl vents it might be more noticeable. Even if you are using gas without ethanol you could be having that issue, gas today isn’t the same as it was in the ‘60’s. Just throwing some ideas out.

[fastf67]

(Yet I am getting a pretty heavy gas smell in some situations). 
Is that only with a full tank or sitting in your driveway, rolling down the road? I would not think you would not get much carb smell driving unless its stop and go consistently. If rolling at rpm I would think more vent from the tank getting fumes back into the body or leak. If you crack the hood and smell is more a leak or carb, running rich. Are spark plugs black? Exhaust heavy with soot? The first initial throttle before rpm and getting a whiff? 50cc accelerator pumps? You running a vacuum gauge? pulling good vac and smelling gas from carbs would have to be rich or i'd look other places. maybe running lots of cam duration and pushing flow back up intake runners, as in just off idle? Trans circuits open and starting to pull from venturis and still getting squirt from pumps with a cam thumping will do it. But sounds like a nice ride. Sorry for babbling.

[GerryP]

Why don't you elaborate on what are those "some situations"?  If it's something like you only smell gas while sitting naked in a pool of butter, then that might not be entirely germane, but other situations might.

[shady]

Gas cap seal or vent? ...and don"t laugh, does anyone else smell it?

[cleandan]

Thanks for the reply's so far. I have been mulling over all the ideas given already.
1) Yes, one possible gas smell could be coming from the fuel tank vent itself. The tank vents under the Cobra but pretty much behind the seats. With the way the wind flows over this car it could be pulling in the smell.
If anyone knows how to verify the gas tank vents is working properly on an ERA Cobra I would like to know.
Who knows, maybe there is a check valve in there that failed...I am not certain other than I see a tube that is not leaking that I know is the vent.

2) The camshaft is a Comp Cams 282S...not too radical in a .030" overbore 427. Edelbrock aluminum heads with lash set cold a .016"

3) Vacuum at idle is about 11-12"hg. It is pretty good and steady with the slightest of gauge needle flutter. (I'm using a 4" diameter gauge)

4) I smell the gas most during hard acceleration, after shut off (vaporizing in bowls I suspect) and sitting at idle like a stop sign. There is a wiff here and there when driving and I am aware I may be hyper searching for the gas smell at this time too...But it is stronger than other dual quad 427's I have driven and worked on.

I am using BP 93 octane pump premium. I could fill up with 100LL av-gas and see if there is a difference. I know the new gas formulas are NOT carb friendly for a bunch of reasons, lower vapor pressure being one of them.

5) I am aware of the vents to atmosphere of Holley carbs and understand the normal smell of engines with these carbs are becoming distant memories, rather than daily occurrences. Pretty much any carbed vehicle will smell some when partked after a full temp drive, but this one is quite a lot more.

The carbs have Ford part numbers so I assume they are Ford original Holleys, not reproductions.

Thanks again.
No ideas are bad at this point...well, maybe the riding naked with a porcupine in your lap idea is a bit sketchy...otherwise they trigger ideas that may get me to a good end.

[KMcCullah]

I am using BP 93 octane pump premium. I could fill up with 100LL av-gas and see if there is a difference.

I'll take the smell of 100LL over any 10% ethanol gas. Plain old ethanol pump gas is pretty stinky stuff. It's designed for cars with emission systems. With vacuum fuel tank systems and carbon canisters.

I'm certain ethanol gas is what ate the guts out of my gas cap. Been running ethanol free 93 Sunoco lately. Smells ok. 

[GerryP]

Although everyone's biology is slightly different, you can smell gasoline at 0.025 parts per million.  In a moving vehicle, that could be a very tiny leak that wouldn't be obvious or easily detectable.  It would depend upon the air flow, but if it was up front, then, yes, you're going to smell it.  A leak at the back would depend on the turbulence.  I'm sure you can feel the wind on the back of your head driving a roadster.  But not all the air is blowing back, so it would take a more substantial leak.

The normal vapor coming from carburetor vents would be slightly noticed in a closed environment, like a regular garage, when the engine is hot.  Vaporization is pretty negligible with a cold engine even in the garage.  There can be some fuel system issues that can cause problems, like a gas tank that is not vented.  I doubt your boosters are leaking fuel since that would cause rough idle and surging.

So, knowing your nose is very sensitive to gasoline vapors and there not being an obvious leak but you can smell gas, I would say it would be in your interest to do some very deliberate, inch-by-inch investigation.  There would have to be some trace fuel evidence somewhere. You already know from experience you shouldn't be able to smell gas in a similar system.

[jayb]

My money's on the carb vents.  Way back when during a diagnostic episode with my Mach 1 I boiled fuel in a beaker on a hot plate to record the boiling temperature.  155F.  No wonder it was bubbling out of the carb vents and flooding the engine.

Quick diagnostic is to put in 5 gallons of race gas and see if the smell goes away.  If it does, the fuel is probably percolating in the carbs and causing the smell.

[cjshaker]

Way back when during a diagnostic episode with my Mach 1 I boiled fuel in a beaker on a hot plate to record the boiling temperature.  155F. 

Wow, that seems crazy low! Underhood temps of most cars have to reach that, easily. I see evaporation percentages at certain temperatures, but never saw boiling points listed. Did you see what the difference was with race gas?

One thought about the smell, while I've never ridden in one, I would assume a Cobra has a lot more sounds, smells and all-around senses bashing than most vehicles. I could be wrong.

[jayb]

I didn't try to boil race gas, but it solved the problem I was having.  I eventually went to a return style fuel system on the car, and re-routed the fuel lines to keep them away from the engine as much as possible, and that solved the problem.  FYI the fuel was 92 octane with 10% ethanol.  Race gas would certainly boil at a much higher temperature.

New cars don't need to worry too much about the boiling point of the fuel, because with direct port injection used on new vehicles, the fuel is under pressure right up to the point where it is injected into the engine.  45+ pounds of pressure raises the boiling point significantly.  The problem I was having was a heat soak issue; I would stop the car, the fuel lines would get hot as the underhood temperature went up, then when I started the engine again after about 20 seconds the hot fuel would go through the needle and seat, lose pressure from the fuel system, boil, and spit out the carb vents, flooding the engine.  Took me a while to figure it out, it seemed like the engine was fuel starved, not flooded, but finally one day I duplicated the conditions while the car was sitting in the driveway, and watched it happen.  The amount of fuel spitting into the carb was rather remarkable...

[Drew Pojedinec]

Fuel line return will not change bk/bj’s having external bowl vents.

[machoneman]

I didn't try to boil race gas, but it solved the problem I was having.  I eventually went to a return style fuel system on the car, and re-routed the fuel lines to keep them away from the engine as much as possible, and that solved the problem.  FYI the fuel was 92 octane with 10% ethanol.  Race gas would certainly boil at a much higher temperature.

New cars don't need to worry too much about the boiling point of the fuel, because with direct port injection used on new vehicles, the fuel is under pressure right up to the point where it is injected into the engine.  45+ pounds of pressure raises the boiling point significantly.  The problem I was having was a heat soak issue; I would stop the car, the fuel lines would get hot as the underhood temperature went up, then when I started the engine again after about 20 seconds the hot fuel would go through the needle and seat, lose pressure from the fuel system, boil, and spit out the carb vents, flooding the engine.  Took me a while to figure it out, it seemed like the engine was fuel starved, not flooded, but finally one day I duplicated the conditions while the car was sitting in the driveway, and watched it happen.  The amount of fuel spitting into the carb was rather remarkable...

Thanks for the research Jay. As your testing showed (and Mach 1 experience) my Mach also has the heat-soak isssue if it sits for say 10-15 minutes after a run. Re-starting is often a bitch as the gas has percolated. Then, after an overnight cool-down, sometimes or more than 1/2 the time it's a bitch once again as most if not all the gas in the Holley carb's fuel bowls has evaporated. Then, it's way too easy with a double pumper to either a.) not giving it enough gas for a restart or b.) way too much gas and now it's flooded. And yes, the culprit is 10% etahnol laced gas as pure gas doesn't do this. Arrgghh!

[My427stang]

Are you running S&H air cleaners?  If yes, two things wrong with them out of the box. 

1 - Incredibly restrictive, which could cause it to run rich at WOT, pig rich, which would then come out of the exhaust.  Can't be fixed by jetting because you are choking it for air,  The fix is to go with a K&N element, which is taller if you have room to rey to get back some surface area.

I have tried to find paper elements that are taller,supposedly an S10 Chevy pickup works, but every brand I have had has been slightly big in OD to fit in the chrome cover.

2 - Repop Ford carbs vent tubes are very close to the lid and depending how you zonk them down can even partially block them.  Fix for this is to file/grind them to an angle toward each float bowl

[cleandan]

I didn't try to boil race gas, but it solved the problem I was having.  I eventually went to a return style fuel system on the car, and re-routed the fuel lines to keep them away from the engine as much as possible, and that solved the problem.  FYI the fuel was 92 octane with 10% ethanol.  Race gas would certainly boil at a much higher temperature.

New cars don't need to worry too much about the boiling point of the fuel, because with direct port injection used on new vehicles, the fuel is under pressure right up to the point where it is injected into the engine.  45+ pounds of pressure raises the boiling point significantly.  The problem I was having was a heat soak issue; I would stop the car, the fuel lines would get hot as the underhood temperature went up, then when I started the engine again after about 20 seconds the hot fuel would go through the needle and seat, lose pressure from the fuel system, boil, and spit out the carb vents, flooding the engine.  Took me a while to figure it out, it seemed like the engine was fuel starved, not flooded, but finally one day I duplicated the conditions while the car was sitting in the driveway, and watched it happen.  The amount of fuel spitting into the carb was rather remarkable...

This sounds like a great job for a GoPro camera in the engine compartment.
I know the fuel is evaporating due to heat soak, and boiling when the engine is shut off because the fuel pressure drops...This is plain science at work and there is not much I can do about it.

I never thought about the fuel boiling so violently that it would erupt out the vent tubes.
Currently I have the floats adjusted so the fuel is just barely at the bottom of the view port threads when slightly shaking the car to check levels.

I wonder if lowering the level a bit more may help. I will know, due to fuel starvation and the engine losing power, if I get the level too low.