66 396/360 valve cover vent hose routing? - Page 2 - Chevelle Tech
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post #16 of 33 (permalink) Old Sep 21st, 18, 11:15 PM
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Re: 66 396/360 valve cover vent hose routing?

Double pumper has mechanical secondaries, rear accelerator pump and no vacuum canister to operate the secondaries. Both carbs can be had with dual fuel feed lines.
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post #17 of 33 (permalink) Old Sep 22nd, 18, 12:45 PM
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Re: 66 396/360 valve cover vent hose routing?

Quote:
Originally Posted by keithb View Post
and what is it. the out side appearance looks the same to me

Keith,


A dual line is just that, it has two fuel lines feeding the carb. Dual line carbs can be either vacuum secondary’s or double pumpers. In the picture above, that carb, has vacuum secondary’s. You can tell by the large vacuum canister on the left side of the picture. This is just behind the devoiced choke assembly and just forward of the back fuel line. There is no accelerator pump in the back bowl.
Double pumpers, will have an accelerator pump in the bowl of the secondary’s and are linked mechanically to the throttle lever to open the back barrels.

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post #18 of 33 (permalink) Old Sep 22nd, 18, 2:04 PM
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Re: 66 396/360 valve cover vent hose routing?

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Originally Posted by Jayhawk500 View Post
Keith,


A dual line is just that, it has two fuel lines feeding the carb. Dual line carbs can be either vacuum secondary’s or double pumpers. In the picture above, that carb, has vacuum secondary’s. You can tell by the large vacuum canister on the left side of the picture. This is just behind the devoiced choke assembly and just forward of the back fuel line. There is no accelerator pump in the back bowl.
Double pumpers, will have an accelerator pump in the bowl of the secondary’s and are linked mechanically to the throttle lever to open the back barrels.
Ok thanks. So why won’t a factory air cleaner base not fit a after market DP carb if there is no vacumn pod it should be more room

1966 Chevelle SS 396/360 M21 3:73 posi. silver/blue buckets

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post #19 of 33 (permalink) Old Sep 22nd, 18, 4:21 PM
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Re: 66 396/360 valve cover vent hose routing?

Back in 1981 when I installed a 800 double pumper holley on my 66 360 hp, the breather tube on my original base hit the rear accelerator pump not allowing the air cleaner base to set down on the carb. The fix was to remove the breather tube from the base, close the hole, in my case braze a piece in to close the hole, and install an AC push in breather, problem solved. I would post pics but I would have to dig it out from it's 32 year hibernation.
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post #20 of 33 (permalink) Old Sep 22nd, 18, 4:53 PM
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Re: 66 396/360 valve cover vent hose routing?

Keith, is that your car pictured above? That's a very nicely done engine.

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post #21 of 33 (permalink) Old Sep 22nd, 18, 5:02 PM
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Re: 66 396/360 valve cover vent hose routing?

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Keith, is that your car pictured above? That's a very nicely done engine.
no its a picture of a 66 L78 that I found on google images to help my question. but I wish I could take credit for that nice work of art

1966 Chevelle SS 396/360 M21 3:73 posi. silver/blue buckets

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post #22 of 33 (permalink) Old Sep 24th, 18, 1:46 AM
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Re: 66 396/360 valve cover vent hose routing?

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Originally Posted by keithb View Post
Ok thanks. So why won’t a factory air cleaner base not fit a after market DP carb if there is no vacumn pod it should be more room
Keith, It's because the rear accelerator pump arm and the elbow on the air cleaner would have to occupy the exact same space, which is to the rear of the vacuum pod.


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post #23 of 33 (permalink) Old Sep 24th, 18, 6:15 AM
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Re: 66 396/360 valve cover vent hose routing?

This was a common modification. Back in the 70's and 80's you could not go online and purchase a new air cleaner and have it the next day so you modified your original. On the yenko site not very long ago a fellow had 5-6 of those removed vent tubes for sale. They sold fairly quick.

Last edited by 25C 70; Sep 24th, 18 at 6:18 AM. Reason: add text
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post #24 of 33 (permalink) Old Mar 25th, 19, 6:39 PM Thread Starter
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Re: 66 396/360 valve cover vent hose routing?

I got a factory base and can confirm that the interference problem is the accelerator pump on the secondaries, not the fuel line. If I had vacuum secondaries I think it would work. With this carb, I'm stuck with a breather. No biggie. Thanks all.
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post #25 of 33 (permalink) Old Mar 25th, 19, 8:04 PM
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Re: 66 396/360 valve cover vent hose routing?

L78 base is GM 6423240
L34 base is GM 6421773

Maybe the difference in the base take care of the interference with the accelerator pump?

Not sure about the hose or elbow if they are different or not.


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post #26 of 33 (permalink) Old Mar 25th, 19, 9:57 PM
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Re: 66 396/360 valve cover vent hose routing?

The difference in the bases was probably due to one being a single line carb and the other being a duel line,center inlet verses side inlet. Both were vacuum secondaries. Jeff where are you, we need your expertise.
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post #27 of 33 (permalink) Old Mar 26th, 19, 10:55 AM
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Re: 66 396/360 valve cover vent hose routing?

Sorry. Responded before I finished reading the rest of the replies

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Last edited by David Bates; Mar 26th, 19 at 11:16 AM.
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post #28 of 33 (permalink) Old Mar 26th, 19, 11:52 AM
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Re: 66 396/360 valve cover vent hose routing?

Quote:
Originally Posted by Jim_66SS View Post
L78 base is GM 6423240
L34 base is GM 6421773

Maybe the difference in the base take care of the interference with the accelerator pump?

Not sure about the hose or elbow if they are different or not.
L34 base had a snorkle with a closed element and the L78 was an open element assembly. The Corvette L88 and Camaro ZL1 in 1969 were the only Chevrolet vehicles equipped with double-pumper (R4296, 3955205) carburetors. I believe it's only the after market Holley carburetors with the 50cc secondary accelerator pump and associated linkage that had the interference issue with the air cleaner base. The 25cc secondary accelerator pump was not an issue. L88/R4296 pics:
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post #29 of 33 (permalink) Old Mar 26th, 19, 5:12 PM
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Re: 66 396/360 valve cover vent hose routing?

L35=325hp closed element with snorkel
L34=360hp open element 1966, 350hp in other years
L78=375hp open element
please correct me if I'm wrong
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post #30 of 33 (permalink) Old Mar 26th, 19, 7:35 PM
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Re: 66 396/360 valve cover vent hose routing?

Quote:
Originally Posted by 25C 70 View Post
L35=325hp closed element with snorkel
L34=360hp open element 1966, 350hp in other years
L78=375hp open element
please correct me if I'm wrong
I mixed up L34 with L35 so concerning Jim_66SS's post I don't have any idea what the difference is in air cleaner base p/n's he posted.

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