Thanks for clarifying that. Trying to describe something like that the
minute I get out of bed on a Sunday morning isn't very effective. You are
exactly correct as far as my understanding goes.
When I bought my 78, there was a problem with that top flap. It would never
open under any circumstances. If you floored the throttle the engine would
just start to flood and falter. I showed it to a mechanic once and as a
quick fix, he disconnected the linkage to that top door. Then when I opened
the secondaries that top flap would open and away I'd go. This had a down
side in that because he disconnected the linkage to that flap, the vacuum
pot on the side was unable to hold it closed for the first second or two
after the secondaries opened. This caused a huge bog especially at low rpm.
It would acually bog, backfire, then VVVROOOOOMM!! When I got a parts car
that had all that linkage intact, I fixed up the carb on the 78. It works
VERY well now.
Correct, the actual butterfly is mechanically controlled by the throttle
position and the top flap (is there a real name for that part?) is
controlled by a few factors. I think there is a light spring on it to hold
it closed. I think it is balanced in a specific way to make it rather easy
to open. The engine "suction" (or vacuum) pulls it open. The vacuum pot on
the side allows it to open only if there is some sufficient instantaneous
manifold vacuum, otherwise it is held closed. I like this arrangement. I
think it is a nice and simple way to solve what some make to be a complex
problem (Quadrajunk for example)
----- Original Message -----
From: <dardal@xxxxxxxxxxxxxxx>
To: <mailing-list@xxxxxxxxxxxxxxxx>
Sent: Sunday, May 04, 2003 11:53 AM
Subject: IML: Vaccum secondaries? Do they open?
Brad, I believe the thermpquad (made by Carter) has secondary operation just
like the Carter AVS. If that is correct, its somewhere between a vacuum
secondary and a mechanical secondary. You are right, that top flapper
thingy
requires engine suction to open. However the butterflies themselves open
with
mechanical activation, so technically, its not vacuum secondary (all the
above
is assuming the operation is similar to the AVS, which I believe it is).
Even
my Quadrojunk in my LeBaron has similar operation (they must have coped it
from
Carter). I like this type of carb because you can adjust the linkage till
you
are absolutely certain that all 4 "doors" are open letting air fill up all
oversize 8 cylinders!
For the gentleman trying to figure out if his secondaries open or not:
disconnect the choke linkage (or warm up the engine till the choke is open)
and
with the engine off, have someone to push the throttle wide open. Open the
flapper valve with your finger and with a flush light, look down the
carburator. The secondaries should be wide open. If not, adjust the
linkage
till they are open.
D^2, 2x68s, both secodaries open ALL the way!
Quoting Brad Hogg <roadhogg@>:
> The Thermoquad IS a vacuum secondary. Meaning that the top flap thing
> stays
> closed until there is sufficient atmospheric pressure differential on
> the
> top and bottom side of it to open it up. This is supposed to decrese
> the
> bog effect of opening the secondaries at low rpm. There is another
> vacuum
> conponent in that the vacuum pot on the right side of the carb will hold
> the
> secondaries closed if there is very low vacuum in the intake (meaning
> there
> is more open throttle and there is rpm to soak it up)
>
> Not a very good explanation but it might help.
>
> BTW, some Thermoquads run great. I have three that do so they're not
> all
> bad.
>
> ----- Original Message -----
> From: "James"
> To: <mailing-list@xxxxxxxxxxxxxxxx>
> Sent: Sunday, May 04, 2003 2:12 AM
> Subject: Re: IML: Pop goes the carburettor
>
> 76 is indeed a Thermocrap. I'm pretty sure it's a vacuum secondary
> carb, but I have seen them open before while in park. Whether they are
> supposed to or not, I don't know.
> Brian Collinsworth wrote:
>76... Thermoquad?
>Is a thermoquad a vacuum secondary carb, or a mechanical secondary carb?
>Reason for the question is, momentarily opening the throttle when not in
>gear usually will not open the secondaries on vacuum sec carbs. It takes
>more load to get the signal to open.
>Brian
>----- Original Message -----
>From: "James"
>To: <mailing-list@xxxxxxxxxxxxxxxx>
>Sent: Saturday, May 03, 2003 8:17 PM
>Subject: IML: Pop goes the carburettor
>
>Hallo,
>
>The beast (76 NYB) is finally back on the road after a long drawn out
>winter that apparently isn't gone yet since it's snowing right now.
> Anyway today was the car's mini tune-up, it got plugs, a dist cap and
>rotor. The plugs weren't fouled this year which made me very happy (go
>Autolite # 86!). I had it out yesterday and I wasn't totally convinced
>that the secondaries were opening, I had accleration, but no real surge
>forward when I gave it some gas. So I let it warm up today for a bit in
>the garage, pulled back the throttle; the secondaries stayed shut. So I
>gave it a little longer to warm up, pushed back the throttle, POP!
> There wasn't much of a flash, but the sound was definitely loud. The
>flash (more like a bright spark) seemed to come from the very front
>corner of the carb, and it distracted me enough that I still don't know
>if the secondaries opened, hehehe. So the moral of the story is my sad
>remainder of a carburettor has given me more reason to rebuild, and
>NEVER look down a carb when playing. I wasn't, and I'm glad in case the
>pop had turned into something more.
>James
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