Well for those of you who like the edlebrock carter style carbs here ya go.
Idle srews: control only the fuel mixture at Idle and have little or
nothing directly related to the cruising or WOT position of your foot.
Metering rods: there is two diameters on the rods and if you look at
them close you'll be able to see the two steps on the rod.
Jets: for simple tuning the jet is just a variable to give you a more
finite adjustment of the metering rods.
"You need Bigger Metering Rods to get more fuel" if someone says this
to you, RUN! as far away and as quickley as possible, never let this
person near your carb with anything other than a polishing cloth for the
air cleaner lid.
"Wire those wieghts open"...just pull out your gun and shoot this
stupid SOB, he's too stupid to own a car.
"Try putting that vacuum hose for the distributor on the bottom
nipple"...send him somwhere to a farm to look at real nipples he has
no Idea what he's talking about...if he picks up a screwdriver get the
sawzall out and cut his hand off.
Never let anyone touch your carb, learn how it works and what to
adjust and when, to get the result your looking for...unless... this big,
fat, bald headed guy with a dirty old Dodge hat on walks up and
asks..."Need some help..." don't even answer just hand him the tool
box, listen and watch....and he likes that green Poweraid stuff during
the day...at night it's ET (Early Times) and Pepsi..no Coke, Pepsi
Ok so here we go, get out your note pads and there will be homework
err ahh trackwork for ya'll this weekend.
You'll need a vacuum gauge, not a good one, I got mine at Sears
here in town for $9.95.
Plug the gauge on the lower port on the front of the carb, this should
NOT have your vacuum advance unit hooked to it.....right? Ok
Now lets get the idle down as low as it'll go without stalling, now start
turning one of the idle screws in until it starts to loose vacuum or the
engine starts to sputter, .....now count the
turns as you turn the screw out until the same thing happens. lets say
your number is 2 so now go in 1/2 of that or 1 right....OK now same
with the other side.
Remember to keep bring that idle down to compensate for your tuning, you want it as low as possible so you can get a true reading on the idle mixture.
Now start all over again..Idle, in, out, count and set.
By now you should have a pretty good smooth idle easy huh....
Now lets watch the vacuum gauge 1/2 turn in 1/2 turn out slowly turn
the screw back and forth no more than a 1/2 turn in either direction
until you get the highest reading on your gauge, thats it your
done.....runs good now doesn't it.....set the idle up to your desired
RPM for most of you using a Edelbrock your probably running a pretty
mild engine so 750-950 is probably about right.
Now crack the throttle off idle...sounds pretty good huh :-))
OK now check your timing and set it where you want it.
Start over and do the whole process again...Idle down..the old in and
out...vacuum gauge and now your done.
Grab a couple of new spark plugs and a wrench, we're going on a road
test. Find a nice lonely road somewhere, install a new plug in any hole
that's easy. Now stand on that throttle run it all the way through first
and about 1000 RPM below your shift point in second, turn off the key
and release the throttle at the same time. Coast to a stop and remove
the new plug, is the porcelin black brown or white?
Brown is good and probably good to go on the other hand if the plug is
white it's lean and if it's black it's rich. We just tested the WOT
mixture and we now have a baseline on that end of it.
OK put in that other new plug, this time drive the car hard but do not
let the secondary's open, you may want to leave the air cleaner off so
you can hear the carb working and keep it off that deep howl that the
secondary's make when they open. This time run it all the way up to
your max RPM and shut down the same way. Pull the plug and install
one of your old ones and head for the shop.
Remember the two different diameters on the metering rods. The rods
are pulled up out of the jets as you accelerate, the first stage or
primary circuit is the larger diameter of the metering rod, the smaller
diametyer or the tip size is your secondary or WOT circuit.
So let's think about this...the SMALLER the diameter of rod the more
fuel right....remember the rod is lifted out of the jet and because it's
thinner at the end as it's pulled up and out of the jet seat, more fuel
is allowed to flow into the engine....make sense?
For this example we'll use a metering rod numbered 40/60, 40 being
the tip of course.
So let's say for example the #1 plug in our plug test was a little dark
brown almost black and the # 2 test plug is almost white. By our test
we know that #1 plug was wide open throttle so our engine needs less
fuel at WOT so the smaller number of 40 needs to increased to say a
But, the primary throttle circuit is showing a lean condition so it needs
more fuel..so...yup, you guy's are smart, we would drop it to say a 55
so now we need to go looking for a set of metering rods 45/55. and
start all over with a couple of new plugs and back to the road.
This is how I do it and to super tune one of these carbs you really
need a spark plug reader and look way down at the bottom of the
porcelin but for most simple applications this will get you so close
you'll never feel any improvement in the seat of your pants.
I used this method 2 weeks ago on my neighbors 80 El Camino (sorry
but someone has to keep them running or they'd be cluttering up all
It's a basic stock 305 last winter we put a Edelbrock RPM manifold, 600
Edelbrock, curved the distributor, headers and he tuned it up to the
best of his ability...it ran 16.40's pretty consistantly but always had a
stumble and was hard starting. I got tired of hearing him crank and
crank the thing and convinced him to let me tune the carb...it didn't
take much convincing....last week the car ran 15.87, 15.91, 15.88 and
broke out in the 1st round with a 15.87 on a 15.88 dial :-((
He checked the milage and it picked up from 14.4 to 18.2! Not
important to me but he liked it.
There's alot more fine points to these carbs but my fingers are tired
and I need to get my ugly sleep. Besides you have lots to work on for
Next lesson we'll discuss:
What those springs that the metering rods sit on do and .....what are
those weights and how do they work?