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Discussion Starter · #1 ·
454 .030 over rv cam th400 3.31 14" wheels
9 MPG
plugs golden brown
total timing set to 40 (ping starts at 42)
holley 4011 spreadbore which appears to be in good funtioning condition.
64 primary jets,
60 secondary jets,
6.5 power valves,
.026 discharge nozzle.
Idle Vacuum = 18-20”

did no better mpg wise and no change in tailpipes after 200 miles with qjet which gene had set up for me
always smell some gas but mostly from vented cap..lotta pressure in sunny florida results in evaporative emissions thru cap
starts real nice in cold with choke butterfly removed

why would my exhaust tips be constantly black and sooty?? is that typical/normal?
(i thought this meant it is rich but not according to the plugs..)

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Rich Baratta
Cocoa Beach, Fla
Team Chevelle #380
May 2001 Feature Car
BSE WannaBe
[email protected]
www.chevelles.com/showroom/70_SS_454.jpg

[This message has been edited by 70 SS 454 (edited 01-15-2002).]
 

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Sounds like my 409! I've tried everything to correct it but no good. I've changed the jets and metering rods and although it did lean it out, I still get the sooty tailpipes. My plugs also run brown in the centers with sooty black on the outer ring. I've been told that big blocks tend to run rich and not to worry about it. My clothes smell like exhuast after a ride though.


I've rebuilt the carb twice. (original Carter AFB) No signs of flooding or heavy floats. I don't even need a choke on it. I have started it up in 20 degree weather without using the choke! It will idle like a champ too.

Maybe someone here will help both of us.


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Bob (Pa.)

1963 Impala 283
1966 Chevelle SS 409
1969 Malibu 307
1972 Malibu 307
1969 C10 stepside 350
1971 Cheyenne 20 3/4 ton
Somebody stop me... :)

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Don't worry about the tail pipes, it's the plugs you need to look at. When you first start up cold, the mixture is rich because the air is colder and is more dense. Therefore to keep the required mixture ratio of around 15:1, you need more gas. If your choke or right foot puts too much gas in the air, then you get the black smoke until it warms up. Your tail pipes don't get hot enough to burn the soot off, so it builds up.
If your plugs are a light brown, then you are good. You might want to adjust your choke if you have one.

Dave
 

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Way back when it was a status symbol to have gray exhaust tips. Today with the weak octane non leaded crap it is almost impossible to get. Be prouder of the color of your spark plugs although nobody can see it but you.
 

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Discussion Starter · #8 ·
thnaks guys..after reading another thread i thought maybe there was something going on that could be changed to give me more mpg
since im not getting gobs of HP

9 MPG and low compression/ hp engines is a crummy combo..
if your "paying " for hp then at least you should have it...some day i will!!



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Rich Baratta
Cocoa Beach, Fla
Team Chevelle #380
May 2001 Feature Car
BSE WannaBe
[email protected]
www.chevelles.com/showroom/70_SS_454.jpg
 

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Discussion Starter · #10 ·

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Have you tried a new power valve Rich? After looking at your carb specs I would bet you could see an hp gain with some 70 jets in the rear and also check your float levels ,I know that mine use to rise a lot when it was hot!
 

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Now that the post has been answered......
when I first read this subject quickly I could have sworn it said "Black Booty...."
 

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Discussion Starter · #14 ·
67johnny

Let me tell you how I established this odd jet configuration

I went to a dyno shop and we played with jets

Original Holley specs for this carb are 60 primaries and 64 secondaries
When I got the car it had 64 X4

On dyno we changed prim to 58 and gained 12hp and slight increase in torque
On the ride home it was surging indicating lean primaries
So I stepped up to 60 primaries which then put me right on original Holley specs (60/64)

It was no longer actually surging but I could feel a slight torsional vibration (that’s the only way I can describe it,,..maybe a very barley noticeable surge)

I knew that 58/64 actually gave me more hp with secondaries open so I didn’t want to go 62/64 or 64/64
So what I did was I switched the primary to 64 and the secondaries to 60 (i.e. switched primaries and secondaries with same jets)
Thinking that this would enrich when just running primaries but that same fuel would be available at WOT (60/64 vs. 64/60) thereby gaining close to the extra 12hp we saw with 58/64
This 64/60 did in fact get rid of that “torsional” vibration and she runs real smooth now.
I don’t know if there more to be had in this holley 4011 650 cfm carb (remember I have an rv cam that runs out of breath starting at 3500 rpms

Is this thinking valid??

Anyway that’s why the primaries are larger than the secondary jets... comments are welcomed!


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Rich Baratta
Cocoa Beach, Fla
Team Chevelle #380
May 2001 Feature Car
BSE WannaBe
[email protected]
www.chevelles.com/showroom/70_SS_454.jpg
 

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Hi Rich! Your carb specs from holley assumes a stock cam in most cases and also you have a spread bore which takes in more air in the rear inlets than the smaller primaries in the front, thus needing more fuel (jet size)than the front does! You did not list the cam specs but I bet they are around 450 /460 lift. The stock jetting in my SBC 780 holley is 70pri/78sec and although I dont remember off hand the cfm of your carb ,the fact you say the power was down and you had some pinging makes me think lean! all the speadbore carbs use a bigger jet in the rear. Give it a try and while your in there make sure it has a 10.5 power valve also! Good luck Rich.Let us know how it goes!
 
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