TQ bowl vent

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Professor Fate

Professor Fate

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I have the usual problem with the carb going dry after a few days (no leaks, all the usual culprits have been addressed), and while it doesn't bother me too much, it bugs the wife... and so I'm pondering ways to make it better. Yes, non-ethanol gas goes a long way to not having this issue, but it's not always an option with a daily and potential long-distance cruiser.
So my thinking is this:
Barring any leaks, the only way to dry out the carb is by evaporation. Evaporation can only occur when open to the atmosphere- it won't happen in a closed system. Later Lean Burn and ESA feedback ThernoQuads addressed this by adding a bowl vent solenoid valve wired to Ign Run. Previous manual valves were open at rest and allowed vapors to escape.
I've got my current carb pretty dialed in and running like a champ, so I don't really want to swap carbs at this point, so my question becomes this:
Has anyone tried hooking up an external 12v NC valve to the vent fitting, wiring it to IGN run? If so, did it prove to be of any benefit? Did it aid in starting after extended periods? Should I just forget about it and go have a beer?
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I don't see how it could. What are your plans for the three bowl vents on the top of the carburetor?
 
RustyRatRod said:
I don't see how it could. What are your plans for the three bowl vents on the top of the carburetor?
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I'm assuming (yeah, we all know how that goes!) that any vapors there would be captured in the air cleaner. Chrysler (Carter) never changed that even with carbs designed with vapor recovery in mind; they just went to the mechanical valve initially, then the electric solenoid valve later on. Just trying to follow their line of thinking. But, that's why I asked- don't know if I'm just barking at a squirrel up a tree or not.
 
Professor Fate said:
I'm assuming (yeah, we all know how that goes!) that any vapors there would be captured in the air cleaner. Chrysler (Carter) never changed that even with carbs designed with vapor recovery in mind; they just went to the mechanical valve initially, then the electric solenoid valve later on. Just trying to follow their line of thinking. But, that's why I asked- don't know if I'm just barking at a squirrel up a tree or not.
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I don't see how that's gonna stop the fuel from evaporating......if that's even what it is. Even if the air cleaner were completely sealed, the fuel would still evaporate into the engine.
 
What do you have for a carburetor mounting gasket? If not, you need the real thick one. It's over .250" thick.
 
I always just put a cap on that vent anyways because the other three are plenty to vent the bowl, and leaving the side vent open can cause a gas smell on deccel and at idle. On the otherhand, I've never had problems with my TQ drying up. It would hold gas in it for over a week at 60 degrees. I was running a blocked exhaust crossover on a 340 cast iron intake with a very thick gasket.





Or you could just get an electric fuel pump.
 
remytherat said:
I always just put a cap on that vent anyways because the other three are plenty to vent the bowl, and leaving the side vent open can cause a gas smell on deccel and at idle. On the otherhand, I've never had problems with my TQ drying up. It would hold gas in it for over a week at 60 degrees. I was running a blocked exhaust crossover on a 340 cast iron intake with a very thick gasket.





Or you could just get an electric fuel pump.
Click to expand...
Yeah, that's what I was getting at- a few days, up to a week depending on ambient temps. Never have any issues with hot starting or sitting for a few days.
Electric fuel pump ain't happening, I'll just live with it before I do that. Like I said, it doesn't bother me too much, but the wife drives it as much or more than I do, and it irks her- sooo, I'm just thinking of some possible options to help slow down the evap a bit more.
 
What kinda intake manifold is on it? I think a lot of these cranking issues come from this bs ethanol fuel pooling in the intake plenum.
 
RustyRatRod said:
What kinda intake manifold is on it? I think a lot of these cranking issues come from this bs ethanol fuel pooling in the intake plenum.
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Factory iron intake ('79 casting date) with EGR block off plate and plenum orifices blocked off.
Hard to imagine pooling only after several days, but who knows? Can't take anything for granted.
Gotta admit, though, this isn't an extreme issue. More like just an annoyance. I'm just getting too old to be annoyed all the time. Or maybe I'm annoyed because I'm old... chicken or the egg.
 
How about this; I mean it's just an idea.
I keep a small plastic bottle of stabilized gas under the hood, with about 5% 2-cycle oil mixed in. My air filter is mounted on top of the hood and the carb is sealed to the underside.
When I open the hood, the Holley is staring right at me. So I squeeze about 50cc of fuel into the float bowl thru the vent, and a lil shot into the primaries. Then return the bottle to it's holder and shut the hood. The rest is normal.
Now, if your Air Cleaner is still mounted to the carb, this won't work for you. But, I bet you could rig a squeeze bottle, or a squeeze-bulb, to the bowl-vent to do the exact same thing. Course, seeing as this is the wife's car, you might be in charge of keeping the squeeze-bulb primed.
If your car has a charcoal canister plumbing, you could pirate the vent line, or take fuel from the pump-supply line, just back of the pump.
I mean these were my thoughts. But, for me, the bottle was just too easy.
However
My Holley is a double pumper and the back bowl almost never dries up. So sometimes I just get in and start pounding on the pedal while cranking, and in a few seconds she lights right off. (no choke) But I don't drive her in the cold months anymore.
 

GTX JOHN said:
Are you sure the two bottom O rings are good and
sealing right?
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I used just a dab of grease to make sure they stayed in place as I reassembled the carb, seemed to compress together okay. And they were ethanol tolerant o rings, too.
The wells didn't leak, either- but I still hit them with a light smear of fuel-resistant epoxy while it was apart, just to be on the safe side.
 
The fix is an elec fuel pump.
There are numerous places on the carb that are exposed to atmospheric air....& evporation...besides the main vents:
- air bleeds
- sec discharge tubes
- idle & transfer ports.
 
I've run an electric fuel pump since the 70's, except the 383 Formula S. The 383 and TQ would suck the bowl dry just after the 2nd to 3rd shift in the 727. The old Carter HP mechanical pump fixed that problem.
 
AJ/FormS said:
How about this; I mean it's just an idea.
I keep a small plastic bottle of stabilized gas under the hood, with about 5% 2-cycle oil mixed in. My air filter is mounted on top of the hood and the carb is sealed to the underside.
When I open the hood, the Holley is staring right at me. So I squeeze about 50cc of fuel into the float bowl thru the vent, and a lil shot into the primaries. Then return the bottle to it's holder and shut the hood. The rest is normal.
Now, if your Air Cleaner is still mounted to the carb, this won't work for you. But, I bet you could rig a squeeze bottle, or a squeeze-bulb, to the bowl-vent to do the exact same thing. Course, seeing as this is the wife's car, you might be in charge of keeping the squeeze-bulb primed.
If your car has a charcoal canister plumbing, you could pirate the vent line, or take fuel from the pump-supply line, just back of the pump.
I mean these were my thoughts. But, for me, the bottle was just too easy.
However
My Holley is a double pumper and the back bowl almost never dries up. So sometimes I just get in and start pounding on the pedal while cranking, and in a few seconds she lights right off. (no choke) But I don't drive her in the cold months anymore.
Click to expand...
I'd like to avoid manually priming if possible- Picture this:
Wife gets up at 6 am to go to work and decides she wants to take the wagon (this is a '66Dart wagon, 360 TQ, btw). She's not gonna grab a primer bottle full of gas and pull the air cleaner off while wearing her office clothes, so-
She comes back into the house and gets my lazy a$$ out of bed to do it for her. Uhm, not optimal.
Normally it's not an issue, since it gets driven several times a week. I guess I can just force myself to go out and fire it up for a few minutes the night before, and not worry about it, but I'm just looking at any little tweak that may help a wee bit.
I've actually got a late TQ with the solenoid vent sitting in a box on the shelf I could go through and try, but I'll have to mod the base to get a vac. advance port among other things, and I've got other projects ahead of that.
I was just hoping someone might know if adding a simple external valve to an existing "known good" carb (or even running a later carb that has the solenoid) would have any useful benefit.
 
For reasons known only to Carter, production TQs came with tiny 0.093" n/seats. Even the AFB/AVS carbs they replaced generally had the 0.101" needle/seats & these had less airflow & therefore less HP potential.
On a 'HP' engine with a production TQ, I enlarge the n/seat to 0.111". This is the same size that the Comp Series TQs came with & is two sizes larger than production TQs.

This is quite possibly why under performing TQs were removed, simply because of fuel supply.
 
Bewy said:
For reasons known only to Carter, production TQs came with tiny 0.093" n/seats. Even the AFB/AVS carbs they replaced generally had the 0.101" needle/seats & these had less airflow & therefore less HP potential.
On a 'HP' engine with a production TQ, I enlarge the n/seat to 0.111". This is the same size that the Comp Series TQs came with & is two sizes larger than production TQs.

This is quite possibly why under performing TQs were removed, simply because of fuel supply.
Click to expand...

And Piglet asked Pooh "Why does the sun go down? It gets dark and scary then."
Pooh replied "If it doesn't get dark, we won't be able to go to sleep."
 
I bought a bunch of Thermoquad Carter perf. /120 Needle and seat sets
Ebay still in original package.

The issue with the Carter .110/.120 is that the only seem to tolerate 6 to 6.5
PSI. The .0865/.0930 are happy with 8 PSI. That being said either one
works fine for use as long as float are good and properly set even in our 9 Sec. Superstockersica

However, I fabricate my own .110 needle/seats that flow more (less restrictive) and tolerate
8 PSI. I am sure it really makes any different but what we do is a battle of inches.
 
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