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Old 02-08-2008, 07:02 PM
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Edelbrock carb needles and spring

Does anyone know which needle is leaner. My carb has a 7047 needle in it. My friend gave me a set of 7147, is that richer or leaner. The 7047 is smaller at the end. He gave me a set of springs also, They are shorter than the ones I'm using. I'd like to lean out my carb a little.

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Old 02-09-2008, 01:12 AM
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7147 is the richer needle, if you did not change your jets.
What colour is the springs??
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Old 02-09-2008, 07:39 AM
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disagree... the .070/.047 needle is richer

(just to illustrate say you have a .100 jet)

when cruising the high engine vacuum holds the .071 fat part of the needle in the hole in the jet obstructing the flow

.100 - .071 = a .029 "opening" available that gas can flow thru
100 - 70 = a .030 opening present which is more flow aka "richer"

when you floor it, vacuum goes away and the spring lifts the needle so that only the .047 thin part is in the hole in the jet

both needles are .047 so with a 100 jet there is no change and alot more gas for a richer burn

by changing from a .070 to a .071 for leaner cruise with a 100 jet then 30/29=approx 3% leaner....that's a pretty small change

my $.02 on the 'springs"
it's more of a question of at what Hg level the carb "should" go richer based on the the whole car and motor combo ....weight/gears/tranny/altitude/major hills/etc....

a weaker spring won't let the carb go richer (lift the needle) until the Hg is lower.....
a stronger spring will lift the needle sooner to go rich with more Hg present

here's a link to the full easy to read manual:

http://www.edelbrock.com/automotive_...ers_manual.pdf

Last edited by red65mustang; 02-09-2008 at 07:58 AM.
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Old 02-09-2008, 07:52 AM
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You may want to go the the Edelbrock web site and download the owner's manual . It will tell you exactly how to tune your carb and which needles, jets etc you net to accomplish your goal.
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Old 02-09-2008, 08:03 AM
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re: Edelbrock carb needles and spring

When you say needle you mean the step up rod? and the spring is the step up spring under the rod plunger. The rods have 2 size of diameters the larger diameter controls the idle/cruise mixture and the smaller diameter at the end controls the power mode mixture when your foot is in the gas. If one rod is smaller on both diameters then it would be richer assuming you are keeping the jets the same. You can't go by length on the springs, they are rated by the vacuum it takes to hold the rod down. I think they range from 3-7 in/hg. A stiffer 7 spring will basically raise the rod faster transitioning the carb into power mode sooner .this would be a richer setup (When you mash the gas vacuum drops). A 3 spring would stay down longer effectively leaning the carb off idle. It takes more of a vacuum drop to raise the rod. Springs are usually used to correct off idle hesitations.
You can download a owners manual from edelbrock here http://www.edelbrock.com/automotive_...ess_main.shtml
.I would read up and understand what is going on before changing anything.
If you are having trouble tuning the carb and it is running rich i would recommend a fuel pressure regulator. I have a 1405 that would act flooded after it sat several hours and then got to start it. The stock pump had 5.5 or 6lbs so i regulated it down to 4.5 and it made a big difference on the tuning and no flooding. Also i would point out that usually these carbs come tuned out of the box very well for small block street engines. If you post your specific problem we might be able to narrow it down for you a little.
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Old 02-09-2008, 08:10 AM
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cboy....your to quick!

I had to go "find" (CRS!) my link to the manual and edit/add it to my post

I answered his question because it is easy to misunderstand the needle/jet/Hg/spring explanation in the manual
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Old 02-09-2008, 08:52 AM
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kleen56....

a caution....

the 1/4" hex screws that hold down the step up rod (needle) cap will twist the hex head off if you over-tighten them....

tighten gently to just plenty snug
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Old 02-09-2008, 09:36 AM
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Thanks for responding. I found out that the needle numbers are actually two separate numbers. .70 x .47 or 7047. .70 is the cruising and .47 is power. Thus a 7147 is .71 in cruise which is leaner? as Mustang mentioned. As for the springs, it's hard to tell, because the color is worn. My carb, what appears, has orange springs, the other is silver? My spring is much longer and has more coils (If that makes sense). I know the front primary jets are .98 and the rear secondary are .95. Why the secondaries are smaller? Got me? When idling, I get some fumes out the rear but also notice a slight stumble in the carb when accelerating around a corner slightly. Only on occasions. I'm going to keep my long spring in and put the 7147 needle in just to see what happens. I may buy the spring kit and switch out various springs also. Any other suggestions?
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Old 02-09-2008, 09:43 AM
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re: Edelbrock carb needles and spring

Quote:
Originally Posted by kleen56
Thus a 7147 is .71 in cruise which is richer.
Actually leaner. But it seems that is what you are wanting so you are on the right track.
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Old 02-09-2008, 09:47 AM
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Quote:
Originally Posted by kleen56
Why the secondaries are smaller?
They don't have rods,,,so they are actually bigger.
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Old 02-09-2008, 09:53 AM
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I really appreciate all the advice and it's excellent advice for sure. Thanks everyone! I've been to the Edelbrock site several times. I think I get overwhelmed looking at the diagram they show for leaner or richer settings etc. I have a Ford 289 and the carb is a 1405 Edlebrock. It runs good, but I know it's not running as well at it should and could use some tweaking. My best bet is to purchase the calbration kit. I was mostly curious on what changed what and why it changed it. You've answered my questions. Lots of variables with these carbs I guess. Maybe it's best to go with, "If it runs, leave it alone" LOL... Does anyone know why Edelbrock has smaller jets in the secondaries then in the primaries? I would think you would want larger jets in the secondaries on WOT (wide open throttle).
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Old 02-09-2008, 09:15 PM
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UPDATE: I switched out the needles from the 70 47 to the 71 47 needles. I kept the same springs in that were in.( longer ones). The car immediately ran better, even on a cold start. I know it's only 3% leaner, but I can see the difference. Went for a 40mile cruise and it ran nice. I noticed also that I don't get as much resonation out of my Flowmaster mufflers either. Or.... maybe it's just my imagination??? Anyways, I thank you all who helped me out.
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Old 02-10-2008, 10:29 AM
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kleen56....

a comment:
for a best performance possible tune up....FIRST you need to set up the distributor spark timing (base timing/total timing/and curve/and vacuum advance).....(that's how you will gain by far the most HP and TQ that you can actually feel)

ex: a factory stock dist has a "compromise" tune up setting so it can/will run at any ambient temp or altitude or gasoline quality.....just bump a stock 289 base timing from the stock 8* base to 10*-11* makes a world of performance difference (the original manual even states "upto 5* additional is allowed for better performance" but that was with 100 octane plus gas)

THEN....you make any carb adjustments as the last step....

my $.02:
depending on which camshaft and rear gears ratio....a .071 rod and .98* jet (98-71=27) is darn close to best street throttle response on a stock or mild 289/302** from my experience......put a .075 rod in it, likely the motor will feel a little "lazy" and want more pedal (98-75=23=a tiny bit to lean)
*the stock 1405 jet is a 100....100-71=29 and that is likely a tiny bit rich at cruise on a stock/mild 289....pull the plugs and read them to tell....
**600cfm is a bit to big for optimum A/F velocity on a stock/mild 289 but they do work/perform pretty darn well all around
footnote: I do stick in a pair of 75/47 rods in my carb for the 4 hours of 3500rpms interstate drive to my daughters home....only takes a minute and definitely helps the mpg


re: stinks at idle"
the idle gas supply circuit is independent/seperate from the rods and jets....adjust the idle screws on the front with a vacuum gauge to the highest vac possible to get rid of most of the stink.....
if the idle adjust screws don't respond, spray a short shot of carb cleaner using the plastic tube taped to the can down the tiny brass tubes next to the rod caps...the brass tubes are the air bleed/vent for the idle gas supply circuit and are exposed to dirt

why are the secondaries jets smaller than the primaries:
the secondaries throttle bore diameter (1-11/16") actual cfm air flow at WOT 3,000+ rpms and a .95 jet gas flow gpm makes a "correct" 13 parts air to 1 part gas mix for max power, no detonation when the pedal is to the floor (on most mild build motors)
(the primary bores are smaller 1-7/16", flow less cfm....have a bigger (but rod obstructed) jet so it is 14/1 A/F at cruise (rod down) and 13/1 A/F (rod up) at WOT on a mild motor)

yeah, the graphs can look overwhelming.....but they are just a nice simple "shortcut" way to do the math (jet and/or rod change gas flow % compares) I posted in my first reply (3% more fuel with a 70 versus 71 rod)

a request:
do list all the details of your motor first (ign/cam/compression/etc/etc....then ask a question...to get a best info reply
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