About that Holley carb ...

[Snag]

After exhausting every avenue locally , today I ordered one on eBay .
I have one already , but everybody says that a 750CFM 4160 is just too
much carb for a 305 small block GM motor even with the mods I've made .
The one I ordered is a 600 CFM 4160 , and it has some differences . The
biggest one is the fuel bowls on the 750 have center pivot floats and
dual inlets vs the 600 has side pivot floats and a tube to feed the rear
bowl . Both have metering plates on the secondaries and in all other
respects as far as I can tell are identical . Is there anything
inherently better about either center vs side pivot floats ? I have a
full rebuild kit that fits both , so it will be torn down as far as they
recommend .
The stock quadrajet has problems , and I'm tired of trying to tune it
. Everybody always told me Holleys are a lot easier , and I've always
wanted to try one so here we go !
--
Snag
“Free speech is my right to say what you don’t
want to hear.” -George Orwell

[Bob La Londe]

Don't have much to add directly, but we ran a Holley 650 with vacuum
secondaries on a 351W in a full size 2 door Bronco. (a little bigger
engine) and it was plenty.

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[Clare Snyder]

On Sat, 4 Jun 2022 18:09:34 -0700, Bob La Londe <no...@none.com99>
wrote:

Unless you have a huge cam in that 305 a 500cfm carb would be
adequate, and the 600 will be as big as you want to go. As for the
floats? if you are going off-road or severe off-camber driving the
center-hung carb will make you a LOT happier. Can you put the center
hung bowls on the 600???

[Snag]

I was wondering about switching the bowls ... which would also mean
switching to the dual fuel inlet setup . I'll see what will fit when the
"new" carb arrives . As far as the cam , the mfr classes it as a "stage
3 RV cam" (Elgin E-922-P) , whatever that means . I think it's pretty
close to what we used to call a "3/4 race cam" . Specs are .444 lift
intake and .466 exhaust , with 214° and 224° duration @ .050 lift (288°
and 298°) . Lobe separation is 112° . I don't think it's all that
radical ... I expected a reasonably decent idle around 800-900 , but I
can't get the quad to run right below about 1500 or so (haven't hooked
up the new tach yet) . Idle speed screw is almost all the way in and the
idle mix needles are making no difference at all . I just totally
rebuilt that carb , everything is spot on the specs and I sealed the
metering needle wells with JB weld . This carb has had a history of long
cranking to start if it's been sitting more than a few hours , like the
bowl is emptying while it sits . I'm just tired of trying to figure this
one out , I usually have no problems with getting a quad to run well .

[Clare Snyder]

Put a good heat insulator between the carb and manifold to help
prevent the bowls boiling dry on a hot shut-down (makng the engine
over rich after a short shutdown - and slow to start after a long
soak.
The "stage 3 RV cam" WILL be lumpy below 1200RPM but unlike the "3/4
race" will be biased twards low end "grunt", not high RPM
performance. Good from 2000 to 4600 RPM. The 922 runs from 2200 to
5400 RPM - more of the "3/4 race" grind. - close to the factory z28
cam of the late sixties. The 921 is basically the L82 cam. Whar CR are
you running? Hopefully better than 9:1

[Snag]

Original C/R was 9:1 , we replaced the .080 dished pistons with .060
over flat tops . The machinist that did all the work figured that I
should be right around 9.5 or a bit more . This guy is known regionally
for his excellent motor work . The motor came with what are supposed to
be the best flowing stock 305 heads , I forget which casting number (816
?) they are . I did a little port matching on them to match the
Edelbrock Performer intake manifold .
As far as the carb , I did use the thick spacer supplied in the carb
kit . The truck has done this from the day I drove it home . I thought
the well plugs might be leaking from researching that problem , so I
coated the bottom of all 4 with some JB Weld - the machine shop guy also
suggested I do that just as a preventive measure . If it's leaking , it
ain't from the plugs . I really wanted to run that original carb ,
nothing in the world sounds like that quadrajet moan when you dump the
throttle , and IMO the balance between performance and economy is very
hard to beat .

[Bob La Londe]

Oh, I should have said that was two different CAMs. First time was
somthing called a 1/4 race CAM. Second rebuild was with an RV (long
duration) CAM. The same carb worked great for both applications. Never
felt like it was leaning out.