CRG Discussion Forum
Camaro Research Group Discussion => Originality => Topic started by: 69Z28-RS on March 11, 2009, 07:28:51 PM
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Most available information says DZ4053 carbs were never 'vented', yet I've seen some on late '69 Z28's that were vented (and that appeared to be factory original).
I'm interested in collecting information from any owners of '69 Z28's that have original carbs with the front bowl vents. Anyone?
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Mine has vents. They have to to fill up and empty out.
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I suspect that cars that show up with vented float bowls were changed. I have never seen any unmolested 1969 Z28 with a vented float bowl. That was 4346 only for this model year.
Jerry
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My 902 dated carburetor is not vented.
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Mine is a 982 I think... Sept car. It had vented front bowl on it when I bought it in 1976 and it didn't appear to have ever been fooled with (the car was only driven by a 'girl'.. :)
The Overhaul manual shows a vented bowl in the service portion for the Holley4150, so I have always believed that to be original???
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Oct 68 car, 10B; not vented. I thought that was on big blocks?
Jimmy V.
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Mine has vents. They have to to fill up and empty out.
I guess I do not understand what a vent is then. Isn't it the vertical tube with the end cut at an angle?
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I think the vent that is being discussed is the small arm from the linkage to the rubber plunger on the top of the front bowl.
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I guess I do not understand what a vent is then. Isn't it the vertical tube with the end cut at an angle?
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Ditto...
I'm left wondering what (where) this vent-thingy that is being discussed here is and where it resides, since it certainly doesn't seem to be what I thought it was either...
Anyone have any pictures that they wish to share of what it looks like to enlighten me and maybe some others who unfortunately may not have a 4053 carb or similar one that has one?
Thanks - Randy
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As Jerry stated above, the 4346 (http://www.camaros.org/images/carb/carb_holley4346.jpg) had it, but the 4053 (http://www.camaros.org/images/carb/carb_holley4053.jpg) didn't. See the CARBURETOR REPORT (http://www.camaros.org/carb.shtml) for more info.
Ed
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I think the vent that is being discussed is the small arm from the linkage to the rubber plunger on the top of the front bowl.
OK. I have seen those on other carbs. Mine does not have it.
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Here's the Holley idle bowl vent setup (on a 3810, but the same parts were used on all idle-vented bowls); 4053's didn't have them.
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John,
Are you aware of any reason someone with a 69 Z28 in the early 70's would have 'Added' the vented parts to a 4053 ??
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As Ed stated, the 4053 carbs did not originally come with the vented primary float bowls, where the 4346 carbs did.
There are only two significant differences between a 4053 and a 4346; the vented primary bowl is one of them, the primary power valve is the other. Otherwise the carbs are essentially identical.
Eric
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Eric, what would the round vent do that the pipe vent would not do?
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Gary;
Honestly, that's still one of life's little mysteries. ???
I never have figured out what benefit it really offers over the main vent in the choke tower. The most plausible explanation I've heard yet is that it offers additional ventilation to help alleviate fuel percolation during extended hot-soak conditions.
For now, that's as good an explanation as any to me. ;D
Eric
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The round tube vent in the choke tower will, at high air velocities (W.O.T.), create a low pressure area in the float bowl. (air rushing over the tube creates low pressure in the tube. That's why it's cut at an angle, to reduce this effect) Adding a secondary bowl vent eliminates this possibility and insures that atmospheric pressure acts on the fuel and not something less than that. Evidently, this was only a problem on higher performance engines capable of high air intake velocity. That's probably why you don't see it on all carburetors.
If you want to witness this effect in action take a look at a Quadrajet on a dyno with the secondaries wide open and you can actually watch fuel pulled out of the float bowl, up the vent tube, and in to the secondary throttle bores. I used to make air dams that disturbed the air flow over the vent tube to eliminate this. It was wild to see it happen.
I know I'm a newbie on here and I hope I'm not boring people to death with my technical ramblings. This just happens to be the only automotive forum I've discovered that has a lot of intelligent people.
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The only rub with that scenario is the fact that the aux. ("secondary") bowl vent on the primary float bowl closes when the throttle is opened.
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I never have figured out what benefit it really offers over the main vent in the choke tower. The most plausible explanation I've heard yet is that it offers additional ventilation to help alleviate fuel percolation during extended hot-soak conditions.Eric
I agree - that's the rationale I recall from my days at Chevrolet Engineering in the 60's. It's even more important now on our carbureted cars, with our more volatile fuels with lower half-boiling points.
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The only rub with that scenario is the fact that the aux. ("secondary") bowl vent on the primary float bowl closes when the throttle is opened.
Yes, you are right about that. I've never seen that vent on a race carb (Holley) I'm thinking it was to take in cooler air rather than super heated thinner air in the air cleaner assembly that would be present during extended idle periods.
The fuel today is horrible. Front end vollatility diminishes rapidly and leaves behind lots of junk. With all the alcohol and MTBEs present you can't let it sit in your carburetor for very long otherwise it will spoil quickly and make a mess of everything.