Edelbrock Carb Tuning

[cuda66273]

Moparman writes...."To tell
you the truth I think that anything stamped
Edelbrock needs to be SH** on and lit ablaze."


Now Now Moparman318 lets not $hit on anything that doesn't look like
a shingle....

"running rich at idle but lean when I am cruising
down the highway"

Yes, lets look at a metering rod and the Edelbrock idle curcuits and
how they work together..bear with me it's late I'm free typing this post
so I may have to repost some other time but I'll try to give an better
understanding of how it all works.

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.

Lesson 2.....

"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.
Lesson 3....

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
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 Baxter's
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.

Secondary circuit...

This is where you need the karma of the Skuza's monkey.

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
45.

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
the roads)

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
now...

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?

How about Secondary circuit timing, accelerator pumps and more.....

Goodnight boys and girls....this IS cuda66 for "Mopar Mystery's"
bringing Mo-Power to ya.

See ya'll at Mission Raceways August 8-9-10...I might even take a
pass in that blown 440 Cuda we're bringing.....good thing I got some
"Depends" for my 50th Birthday.....

Oh ya almost forgot...

Depends, Edelbrock and any other products mentioned here are for
comparitive puposes only and their mention is no way to be constude
as an endorsement of their products...unless of course they send me
money which I always need

Eddy Carb Tuning Chapter 2

Edelbrock Carb Tuning Chapter 2:

Well I guess it's time to start getting everyone dialed in on their Eddy carbs, so here we
go. In previous postings I've gone over fuel delivery and basic set up so I'll presume at this
point everything has worked out and the carb your working on is in top condition.

In this chapter of the infamous book we'll look at the baseline of the carb and fine tuning
the transition from idle to WOT.

I continually see Guy's buying a new Eddy and immediately going inside and putting in
bigger jets and smaller rods thinking that this will get them more fuel for their motor, when
in actual fact it gives you more fuel but your not changing the air volume so you just end
up with a rich condition and a "Bog on acceleration"

Let's look at one of the most common complaints that I run into on Eddy carbs.

1. Stumble off Idle

Cause 1: Usually caused by a lean condition for a fraction of a second while the plungers
and springs lift the metering rods and dump the required fuel demanded by the engine.

Cause 2: Not enough initial timing in the motor.

Cause #1 Cure: As the vacuum drops in the manifold it allows the spring under the
metering rod to lift the rod out of the seat and dump fuel. So if you having a little stumble
or hesitation it's usually the spring rate. If you go to the next stronger spring it will allow
the metering rod to open quicker and dump fuel sooner in the transition between Idle and
WOT, of course this is assuming that everything else is in good working order such as
accelerator pumps and timing curve.

By changing jets or richening the metering rods (smaller) you will increase the fuel to air
ratio but not change the timing on the metering rods so you may end up with a stumble
and then a bog until the engine picks up enough RPM to burn all the fuel…sound familiar?

Cause2 Cure:
To fully explain the theory behind this I want to revert back to the basics of camshaft
overlap and the science of the 4-stroke performance engine.

For those engine Guru's out there you can skip this part….

Overlap definition: The position of the valves on the exhaust stroke where both the intake
and exhaust valves are open. This is what creates that lumpy idle and reduces the cylinder
pressure on a race cam at idle and virtually destroys the power band at low RPM.

So what happens?…..When the piston reaches almost TDC on the exhaust stroke and the
spent fuel is being forced out of the combustion chamber the intake starts to open allowing
fresh fuel to rush into the cylinder across the piston and be scavenged by pure velocity out
the exhaust valve basically flushing the combustion chamber clear of exhaust gases.

So now based on the ramp speed of the cam lobe and the exhaust valve slams closed so
the intake can refill the swept volume of the cylinder on the down stroke. Now if everything
is right and the valve size and carb can create enough velocity (or air speed) as the piston
heads toward BDC the fuel charge will continue to fill the cylinder when the piston stops
and hesitates for that split second at BDC basically overfilling it or actually building a slight
amount of pressure in the cylinder. The intake valve slams shut and captures the
pressurized fuel charge. Now we have more cylinder pressure than a static or ambient
measurement of volume and we make more HP. A blower or turbo charger just exaggerates
this phenomena.

So how does this affect the carb tuning?

In an overview we can say that we've increased the amount of fuel in the cylinder through
volumetric efficiency and we've decreased cylinder pressure at idle or as they say, before
the cam comes in, so we need to burn all that fuel we've stuffed in there with relatively low
compression or cylinder pressure.

The only way to do this is to give the flame in the chamber a longer shot at it, so we do
this by increasing the idle timing therefore allowing the combustion chamber a longer
duration in the cycle to burn the fuel, this is why at idle if you start to turn advance into
your motor it will pick up RPM, you not adding any fuel or air your just giving the engine
more time to burn what's available.

In conclusion what we've done by advancing the idle timing is burn all the fuel in the
combustion chamber, eliminated the rich idle condition and removed the stumble off idle.
Depending on how radical the cam and the volumetric efficiency you've created with your
combination, this will determine the amount of advance at idle is required for the best
response off idle for your engine.

Stock: 10-12* or maybe even less
Mid range cam combo maybe around 18-22
Stout runner, try around 25
Full blown racecar…you may have to go up to 30*

Just one more note here…. before you can get your distributor curved correctly you need to
go through this tuning process to determine where to set the idle advance and it's
relationship to the max timing and the RPM you want all this to happen at.

Let's use this quick scenario…. you set your engine up incorrectly and you've got the idle at
1200 to make it run smooth, the idle timing is at 12* and max advance of 38* comes in at
2500 RPM and you send you distributor out to have it curved to this spec.

Then I come along and retune it correctly and advance the timing to 22* and idle it down to
1000 RPM, when I moved the idle timing up it also moved the timing up on the other end
so now at 2500 RPM your max timing is now 48*...look out a melt down is about to occur.
This also reinforces the need for a timing light that you can dial in to determine the MAX
advance, setting a performance motors timing from the idle mark is Russian Roulette.

Well that's it for today, I need to go out and try and pay some bills…

This is….cuda66273 for Mopar Mystery's

The Edelbrock Corporation, any of their Dealers, Affiliate Company's or Employees have not
authorized this article. The Edelbrock name is a registered trademark and used for
Identification purposes only. All modifications to a stock engine should be done by a
trained professional and not attempted at home. The author assumes no responsibility for
the results of attempting the modifications as described or implied.

Don't forget to rate the t

[Doug Wilson]

Don, I made one post to a guy that was going on a cross country trip, and advised him to wire the secondaries shut on his AFB. He wanted maximum fuel milage, and having done this before, myself, I found my overall milage improved by about 2 MPG. If you have a car that likes to run, it's tough to keep your foot out of it. Of course, this may be something you have never experienced!

[cuda66273]

I only know 2 throttle positions....
1. Wide open bouncing off the chip
2. Wide open waiting for the shift light

[Bigfoot]

cuda66273:Great write up. I had a leanburn setup on my car and have recently converted over to Electronic Ignition, recurved a vacuum distributor and installed a Edelbrock 1406 carb. I was going to start to tune/play with it this weekend and your little "How to Guide" will come in handy. Have you ever tried a air/fuel mixture meter while driving to set up a carb? In my exhaust manifold sits a now useless o2 sensor that was used in my leanburn setup and I was thinking of rigging up a small circuit to tell me if I am lean/rich I guess as further proof of the spark plug method of reading. Just wondering you thoughts on using an air/fuel meter as a tuneing aid or is the spark plug method better?

[72Challenger]

Reading plugs is an art, and a tricky one at that. If you're not an artist, then reading an O2 sensor is perfect for a technician. I'm no artist myself, I prefer the tech gadgets. Plus, the gauge can give you readings at any throttle opening. There's a reason that closed-loop fuel injection systems use the sensor to fine-tune mixture while running. Because they work!

[Doug Wilson]

The only thing wrong with the "meter" approach, is that, while you get an overall indication of how the engine is doing, you don't get a picture of each individual cylinder. The only way you could do that is with a sensor at each exhaust port. I have considered doing that with EGT (exhaust gas temperature) sensors at each port, and 1 meter with a selector switch on the dash. A project for another day...

[72Challenger]

Good point Doug. The plug readings can tell you if you've got a mixture distribution problem, the meter can't. A meter could still be good for anaylzing changes made after you've verified correct distribution, however.

[Doug Wilson]

Does anyone remember the controversy and puzzlement about the NASCAR chebbie engine that Smokey Yunick built which had about 3/16 holes drilled in the top of each header tube? I think he was using the holes to eyeball the flame color out of the ports, for tuning mixture distribution. I tried it on a smallblock frood, and all I got was a set of headers with little holes that needed to be welded shut!

[73Challenger11@]

Originally posted by Doug Wilson
I tried it on a smallblock frood, and all I got was a set of headers with little holes that needed to be welded shut!

LOL

[moparman318]

Ok cuda. Did the spark plug thing and come out with a WOT plug that come out almost brand new. The only color that I can see is on the inside porcelin about half way down. a little bit of black. Rich then I guess. Well I guess that It's not the carb thats causing my problem. Yes it needs tuned but hey I need to get the overheating problem solved first.

[cuda66273]

Moparman: it could be that your running a little lean at WOT, this can also indicate that your plug is too hot and burning off all the color that should be showing, but you need to look way down inside that plug where the porcelin meets the case.

I've drawn up a quick sketch to try and show you what your plug should look like if all is perfect.

I hope this helps some.....

That little bit of black your seeing probably came from your launch when you nailed the throttle.

This is tough without being able to put my hands on that carb....there's alot of feel that goes into tuning a performance motor and if it could be done by setting perameters in writing Edelbrock and Holley would have done it by now. I need to hear the idle to WOT throttle response of the motor....how it comes off off the idle when you slap it to 1/4 open, smell the exhaust, watch the vac gauge.....twist on the distributor.....you just gotta have a feel for it and know what end result your looking for.

I can only show you the theroy, the gut feeling will come with experience, practice and test runs at the track.

After tuning th Fish last week we cut our best 60 foot time yesterday from a 1.699 to a 1.675 and the conditions were worse than poor.....85% humidity, 74 degrees, 29.2 barometer with a 20 MPH head wind and we still ran 12.278 after a rain storm passed and washed the track clean...I calculated from previous time slips that the car would have run a 12.20 flat or better if conditions had of been close to our previous best run of 12.270 which was 42%H, 65*, and a tail wind of about 10 MPH.

Unfortunatly, we rained out after the first round and weren't able to really get a good read of what we had gained, hope the weather is better in Canada this coming weekend....oh ya... we won that round.....took out 5th place and 3 time track Champion and his 502 Chebby...cut him down at the tree like an over grown rose bush and dumped on him right at the stripe for a MOV of .003...and the Crowd went Wild!

[cuda66273]

Hummmm...lets try the pic again

[Racerjr]

Cuda,
I would like your opinion on what size Demon carb I should buy?
Recently I have read some articles on carb size and it seems as if
the bigger the carb.(to an extent) the faster you go? I dont know what cfm the 340 six pack was, but it made the most horsepower.
I run a 750 Holley AD now and Scott at Barry Grant recommended the 750 race demon. I was thinking of getting the 825 race demon and also order the AD boosters. This is what its going on.

'71 Duster no electronics bracket race car.
360, stock 10/10 crank,stock rods,KB pistons,10.4 to 1 actual compression ratio,Crane 580/560 solid cam,self ported "J" heads
with stainless 2.02/1.65 valves,edelbrock victor 340 intake.
904 trans and 8.75 rearend with 4.88.

Best e.t. 11.23@119.25 mph.

I want a 10.?? time slip! Help! Thanks,racerjr.....

[moparman318]

Ok cuda could ya help me decifer this. This is the plug I ran at WOT It's the recomended plug for this truck. It's heat range is The only color I can see other than the bit of black Is what appears to be some rusty color on the bottom. Not much just enough to make me think that there is some there. Sorry about using your pic but I really hate computers and had no luck in trying to get a some sort of picture of my plugs in this thing.

[moparman318]

Cuda: Here is the other plug I have. It's a 4 heat range and don't look to good. The inside is all sooty black but the porcelin is a rusty red. The red kinda turns to a whiter color just below the end of the threads. I had these plugs in when I bought the truck and were fooling around with them and left them in on a road trip. Givin these two plugs and the best description I can give, what would you say to do.

[cuda66273]

I'm gonna have to agree with Scott on this one, I'm sure he got more details than you gave me here but remember that 750 R Demon is going to perform like a 850 box stock Holley.

The mistake I see most often is too much carb and too much cam.

If you want to see the 10's cut the heads a little more to 11+:1, order a Racer Brown Cam and a Dynamic convertor.

That's a hell of an ET for a 360! That last quarter second isn't gonna come cheap or easy....I would guess your on the edge of your rods and pistons. You are bracket racing?...consistancy consistancy consistancy....Mopar + Demon + Racer Brown + Dynamic = Consistancy to the power of four!

Have you done the math on convertor slippage yet?
If not can I help you with that calculation?

Maybe just the carb and the convertor will get you there?

[cuda66273]

Moparman,

I can't open that attachment?????

Can you post it as a jpeg?

[moparman318]

sure here's the first one.

[moparman318]

here is the second

[cuda66273]

I got them that time...

I like to see a dark ring around the bottom of the plug like that but I like it to be about ...maybe... .030 wide, if it's any wider you may want to jet down a little.

Have you done the vacuum test at WOT on this car yet?

[73Challenger11@]

Hey Don I got my 650 and I was wondering if I can use the throttle adapter off of my old Edelbrock or if I have to get a new one?

[MoJoe]

O.K., Cuda, when can we expect the next chapter in the continuing saga of the Edelbrock Carb?

We're all ears, and patiently awaiting to hear about springs & things.

MoJoe

[Doug Wilson]

The old throttle adapter will work fine. I'm assuming these are both AFB style carbs?? I didn't know that the AFB style had one available with a 650 cfm rating.

[73Challenger11@]

Doug I posted that reply in the wrong thread.It should have been in the Demon thread

[Dr. Righteous]

I have delt with Edelbrock's AFB knockoff carbs since they started making them in the mid 80s. HANDS DOWN they are an excellent and reliable carb. MOST of the time if you choose the correct model they work very well out of the box.
The BEST thing about them is that they are a very forgiving carb unlike a Holley. Sure a Holley is probably better suited for racing when you are at WOT. But most of you guys drive your MoPar on the street and how long do you usually stand on the gas petal?
I have heard many people moan about WOT lean out and midrange power. MOST of them cured the problem by finally finding the small vacuum leak that was causing it, then put the carb adjustments back where they were in the beginning.
Also, many people blame the carb when they have not even got their iginition advance curb nailed down correctly for their setup. The carb is easy to blame when people don't do their homework.
I have owned 4 Edelbrock Performer Carbs on 4 different vehicles since they started producing them and every problem I have ever had was something I did wrong.

[Fred]

cuda66273
I tuned my Carter 625 as to your post.
I think I did a good job on my 318.
I have 95 / 98 jets and 75 / 47 Rods.
The car now has a strong steady acceleration( for a 318 ) All the way up from 0 to 80 mph.
And now a smoth Idle
Never did that before

Thanks
Fred..

[Bigfoot]

Fred: Just wondering what car you are running your 318 in and have you done any internal work to the motor etc. I am going to switch my brothers 318 New Yorker over soon and I have always run thermoquads but my brother I think will go for the edelbrock/carter. Have you had a chance to do a mileage test yet, it sounds like it is running correctly and pulling good. That is one thing that a carter/edelbrock has over the thermoquad is the ability to change parts easily, the thermo works great once it is dialed in correctly but can be a real headache getting to that point.

[Fred]

Bigfoot
I have a 72 Satellite Sebring 318 auto
Very mild Hop Up
Carter 625 on a Holley Street Domonator
MILD MP .410"/.425" lift . 248/256 dur. cam
MP electronic ignition upgrade
2 1/4 " dual exhaust with flow through mufflers
8 3/4 with a 3.23 open
NOT bad for a 318 in a 3800 lb car

[Bigfoot]

Kind of a stupid question but is the Carter Comp. Carbs exactly the same as the Edelbrock Carbs? I know they are both made by Weber (as fas as I know). Can the parts for the Edelbrock be used on the Carter? i.e. rods,jets and rebuild kits etc.

[Doug Wilson]

Yep.