4bbl carb disable the secondaries

one of the new Edelbrock AFB's or AVS's might make a nice choice.
Holley makes a spreadbore that should theoretically be closer to your
old QJ in terms of throttle response and economy... but it's a Holley.
tuning it could become a hobby in and of itself. Alternately you could
have your present carb completely gone through instead of just kitted by
a carb restoration shop, in which case it will probably be good for
another 200K miles or so.

good luck,

nate

chevyengine wrote:
> The carb uses fuel, has to be rebuilt every year because the power pin
> sticks and the jets have to be rejetted in order to get proper fuel
> milage.
>
> The engine does not have many miles on it.
>
> I am looking for an alternative to the 4bbl quad.
>
>
> Thanks in advance
>
> silicon212 wrote:
>
>>chevyengine Wrote:
>>
>>>I would like to disable the secondaries on the 1979 Chevy 4bbl carb. I
>>>have not found any information on how it's done.
>>>
>>>I looked at the carb and saw linkage coming from the vacuum diaphargm
>>>going to the secondaries. Is this the linkage?
>>>
>>>Is there any information on how to disable the secondaries?
>>>
>>>
>>>
>>>Thanks in advance
>>
>>Why do you want to do this?
>>
>>
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>
>


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I see linkage on the driver sider at the bottotm of the carb. It looks
like the crab might need to be removed from the car to remove the
linkage. There looks like there is a spring assembly where the linkage
is. If the linkage is removed the spring assembly would need to be
reassembled?

Thanks in advance.

jeffcoslacker wrote:
> Just remove the link rod between the primary and secondary
> linkages...then they are inoperative.
>
>
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chevyengine Wrote:
> I see linkage on the driver sider at the bottotm of the carb. It looks
> like the crab might need to be removed from the car to remove the
> linkage. There looks like there is a spring assembly where the linkage
> is. If the linkage is removed the spring assembly would need to be
> reassembled?
>
> Thanks in advance.
>
> jeffcoslacker wrote:
> > Just remove the link rod between the primary and secondary
> > linkages...then they are inoperative.
> >
> >
> > --
> > jeffcoslacker
> >
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It's been a while...but yes, I think you have to pull the carb off the
manifold, flip it over and perhaps remove the throttle plate (bottom
section) to be able to disengage the linkage...they have a little ear
on the ends that will only allow removal from certain angles...that is
without bending the rod, which you can do if you don't want to mess
with all that, but no guarantee the rod can be straightened correctly
if you need it again.

I'm trying to think which spring you see...if it returns the
secondaries to rest position after opening, it has to be there to keep
them closed. If there is no spring tension closing them with the link
removed, you'll have to block the secondary throttle plate closed
however you can, or they'll try to slowly fall open, and cause
flooding...


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jeffcoslacker Wrote:
> It's been a while...but yes, I think you have to pull the carb off the
> manifold, flip it over and perhaps remove the throttle plate (bottom
> section) to be able to disengage the linkage...they have a little ear
> on the ends that will only allow removal from certain angles...that is
> without bending the rod, which you can do if you don't want to mess
> with all that, but no guarantee the rod can be straightened correctly
> if you need it again.
>
> I'm trying to think which spring you see...if it returns the
> secondaries to rest position after opening, it has to be there to keep
> them closed. If there is no spring tension closing them with the link
> removed, you'll have to block the secondary throttle plate closed
> however you can, or they'll try to slowly fall open, and cause
> flooding...

The link in blue is the one you want to drop...there may be one side or
the other a screw holding the bellcrank (the part the link fits into),
so you can remove the bellcrank, move it around to where you can
disengage the link, then put it back on...like I said it's been too
long, you'll have to look.

Is the red circle the spring you spoke of? That's part of the cross
shaft, it stays put...

Make sure you completely remove the link, don't just drop one end, or
it will jam your throttle open (don't ask how I know this:banghead:
:lol: )



[image:
http://www.intruderalert.com/cafe/lo...0x%20398).jpg]


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The red circle is what I was talking about.



jeffcoslacker wrote:
> jeffcoslacker Wrote:
> > It's been a while...but yes, I think you have to pull the carb off the
> > manifold, flip it over and perhaps remove the throttle plate (bottom
> > section) to be able to disengage the linkage...they have a little ear
> > on the ends that will only allow removal from certain angles...that is
> > without bending the rod, which you can do if you don't want to mess
> > with all that, but no guarantee the rod can be straightened correctly
> > if you need it again.
> >
> > I'm trying to think which spring you see...if it returns the
> > secondaries to rest position after opening, it has to be there to keep
> > them closed. If there is no spring tension closing them with the link
> > removed, you'll have to block the secondary throttle plate closed
> > however you can, or they'll try to slowly fall open, and cause
> > flooding...
>
> The link in blue is the one you want to drop...there may be one side or
> the other a screw holding the bellcrank (the part the link fits into),
> so you can remove the bellcrank, move it around to where you can
> disengage the link, then put it back on...like I said it's been too
> long, you'll have to look.
>
> Is the red circle the spring you spoke of? That's part of the cross
> shaft, it stays put...
>
> Make sure you completely remove the link, don't just drop one end, or
> it will jam your throttle open (don't ask how I know this:banghead:
> :lol: )
>
>
>
> [image:
> http://www.intruderalert.com/cafe/lo...0x%20398).jpg]
>
>
> --
> jeffcoslacker
> ------------------------------------------------------------------------
> jeffcoslacker's Profile: http://www.automotiveforums.com/vbul...?userid=219638
> View this thread: http://www.automotiveforums.com/vbul...d.php?t=614598
>
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Steve Walker wrote:

> chevyengine wrote:
>
>> I would like to disable the secondaries on the 1979 Chevy 4bbl carb. I
>> have not found any information on how it's done.
>>
>> I looked at the carb and saw linkage coming from the vacuum diaphargm
>> going to the secondaries. Is this the linkage?
>>
>> Is there any information on how to disable the secondaries?
>>
>>
>>
>> Thanks in advance
>>
> This is a Rochester Quadrajet. The vacuum diaphragm is a delay mechanism
> to keep the back two barrels from opening too soon and bogging the
> engine down. You can zip tie through the part that comes out of it to
> keep it retracted all the time. The bottom butterflies will still open,
> but the top air valve will stay shut, and the venturies will see no
> airflow, therefore no (or VERY little)fuel flow in the back barrels.
> However, your engine may run very lean during high demand, as the front
> jets cannot flow enough to feed the engine properly at times of high
> demand.
>

Wrong, wrong, and WRONG.

Disabling the secondary air-door WITHOUT disabling the butterflies below
it will result in, effectively, a closed choke on the secondaries.
Massively over-rich, huge clouds of black smoke, enormous fuel
consumption, fouled plugs, etc.

If you want to disable the secondaries (why on earth WOULD you? It won't
really help mileage and will remove your ability to safely merge on an
interstate) the way to do it is remove the linkage from the main
butterflies to the secondary butterflies so that the secondaries never open.

Steve Wrote:
> Steve Walker wrote:
>
> > chevyengine wrote:
> >
> >> I would like to disable the secondaries on the 1979 Chevy 4bbl carb.
> I
> >> have not found any information on how it's done.
> >>
> >> I looked at the carb and saw linkage coming from the vacuum
> diaphargm
> >> going to the secondaries. Is this the linkage?
> >>
> >> Is there any information on how to disable the secondaries?
> >>
> >>
> >>
> >> Thanks in advance
> >>
> > This is a Rochester Quadrajet. The vacuum diaphragm is a delay
> mechanism
> > to keep the back two barrels from opening too soon and bogging the
> > engine down. You can zip tie through the part that comes out of it to
> > keep it retracted all the time. The bottom butterflies will still
> open,
> > but the top air valve will stay shut, and the venturies will see no
> > airflow, therefore no (or VERY little)fuel flow in the back barrels.
> > However, your engine may run very lean during high demand, as the
> front
> > jets cannot flow enough to feed the engine properly at times of high
> > demand.
> >
>
> Wrong, wrong, and WRONG.
>
> Disabling the secondary air-door WITHOUT disabling the butterflies
> below
> it will result in, effectively, a closed choke on the secondaries.
> Massively over-rich, huge clouds of black smoke, enormous fuel
> consumption, fouled plugs, etc.
>
> If you want to disable the secondaries (why on earth WOULD you? It
> won't
> really help mileage and will remove your ability to safely merge on an
> interstate) the way to do it is remove the linkage from the main
> butterflies to the secondary butterflies so that the secondaries never
> open.

It's not as bad as you might think...we had two wreckers at the shop
that had secondaried disabled (because the boss was the cheapest
******* you ever met), and both would tow adequately, albiet not very
swiftly...but when I opened them up on a trial basis, fuel mileage
plummeted, and he made me change them back...Tried to convince him that
a large 2 bbl would be a good compromise, but that would cost MONEY,
see, and well, that just wasn't going to happen...

At least it was good practice. Towing a full sized conversion van with
a 350 breathing through the primaries of a Q-jet only was very much
like driving the 80,000 lb GVWR rigs I currently run...very slow
accelerating and use your gears wisely...:lol:


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