Edelbrock 600 carb on 383

[frederick]

Hi,

Went out today to tune the Edelbrock carburettor after finally completing the engine rebuild/upgrade.

New specs:
383 +0.030
440 source Stealth heads
9.7 compression
Edelbrock performer intake
Edelbrock 1405 600 cfm carburetor
Lunati 262/268seat 220/226@0.050" 0.475"/0.494"
1.75"headers
Timing: 13deg at idle, 34deg max

Did a few tests and it looks like the carb is way too small.

It was bogging with the accelerator pump arm on the standard, center hole, so I put it closer to the carb.
This cured the bog almost completely, but I can still see it going lean on the wideband sensor whenever you start accelerating.
However when you suddenly give it full throttle it backfires.
Would a bigger accelerator pump nozzle cure this?

Also did a test at WOT and at 3000rpm it's already pulling 2"Hg.
I checked to see if the throttles are opening fully and they are.
Is it normal to have that much vacuum so early in the rpm range?
The articles I've read suggest 1.5"Hg at max rpm.

Another this that suggest the carb is too small is that I can't get the transition slot squared.
If I do square it, it stalls even with the vacuum advance hooked up to manifold.

What would you suggest?
Get the accelerator nozzle kit and tune it or get a different carb?

[ChgrSteve67]

Are you running the rods and jets that came with the carb?

I have a 650 and the rods and jets that came installed ran my motor pretty lean.

Get one of these
http://www.summitracing.com/parts/EDL-1479/?rtype=10

and if you look in your carbs owners manual there is a Calibration Reference Chart page.
http://www.edelbrock.com/automotive_new/mc/carbs_acc/pdf/carb_owners_manual.pdf
Look at page 12

Its shows the rods and jets you need to richen up the fuel mixture. I started at stepping mine up 2 stages for both cruise and power.

after that its a matter of going up or down to get the afr where you want it.
The kit gives you a fairly good range of adjustments however you may need to by a set of rods or jets that are not in the kit to get it just right.

My accelerator pump is still set as it came out of the box.

Hope this helps.

[frederick]

Today I just ran with the stock rods and jets that came with the carb to get a good baseline.

I've got the calibration kit as well but haven't tried it yet.

Don't think it's the cruise and power mode of the rod that's the problem, but the inadjustability of the accelerator pump.

Cruising AFR is 12.5-13, so much to rich.
When you push the accelerator it immediately goes lean; 14-15

[ChgrSteve67]

the accelerator pump just gives an initial shot of gas to prevent stumbling.

Change your Step-Up Spring and see if it helps.

Read second half of page 4
There is also a good picture for the rods and Step-Up Spring

[frederick]

Hi Steve,

Thanks for the help.

Did some more tests.
Standard Step-up spring is 5"Hg changed it to the silver 8"Hg made no difference.
It still goes lean when you accelerate, which isn't really surprising cause I have to go almost full throttle to get below 10"Hg
Think I need a spring that's rated somewhere around 12"Hg to have the power mode come on quickly enough.
Trouble is Edelbrock doesn't have such a spring.

Checked the accelerator pump again; good squirts from both jets and no lag.
Should I try bigger nozzles?

[mjwebb]

i have that carb matched to their intake on my mildly built 383 and richened up the metering rods..my car starts and runs like a dream...but I have highway gears with the 8 1/4 axle..it's no screamer but a sweet driver...I think sometimes people over carb their engines...but many are more of a hot rodder than me

[ChgrSteve67]

Since you have the kit I would up the rods a stage or two and see what happens.

At idle my charger runs around 13.7 and under power its between 12.3 and 12.7

I don't have a vacuum gauge so I can't help there.

[Manifold]

I'd say you need to up your initial timing. What method did you use to determine 13 degrees was what you needed? I'd suggest using a vacuum gauge. Find the amount of initial timing at idle that will give you the most vacuum, then back the timing down to get a 2" drop in the vacuum. Then, adjust the mechanical advance to give you the total overall you want (or use the vacuum gauge to determine the total the motor likes: with the distributor loose enough to turn, bring the RPMs up to the point where the timing is all in [by 3000 RPMs at a minimum - if it isn't, recurve the distributor], rotate the distributor to find the amount of total timing which will produce the maximum vacuum reading).

After the timing is mapped out, then turn to the carburetor. Do the Eddy carbs have a stop screw on the secondary throttle blade shaft? My Carter Comp Plus AFB isn't within easy reach to check. If you can't get the car to run with the transition slot squared, I use the technique of slightly opening up the secondary butterflies with the stop screw to allow some more air to flow into the engine. This will bring the RPMs up to a level which will let the engine idle with a squared transition slot (think of it as a controlled vacuum leak - a big vacuum leak will have the engine idling way high, a small one being controlled by you will help you out in this case. BG Demon carbs with Idle-Eze work this way - provides a controlled, metered source of add'l air for the engine.) If you can't get enough air through an adjustment of the secondaries with the stop screw, then you can move to drilling holes in the primary throttle blades... though I don't think you'll have to go that far.

[ACUDANUT]

As a rule of thumb, 600 cfm's go on small blocks....Big blocks run better with at least a 750 cfm.  Anyway, I'm also partial to the Holleys, as the aftermarket air cleaners do not sit right on the Elds.    Goodluck.

[flyinlow]

I have an Performer 800 on my 440. A/F gauge showed idle 13:/1 (smoothest idle) 14-15 :1 under light acceleration after the initial rich spike from the accelerator pump. 14:1 at cruise. Low 12.5:1 at WOT. Ran well at those settings .

Thermoquad/ SD intake runs 16:1 under light acceleration and 15:1 at cruise.  12.5:1 WOT

You should be able to drop the vacuum below 10" anytime you want. 1.5" WOT at 3000  RPM is too much too soon.

With an assistant flooring the car do both pri/sec open all the way?

Run about 24* timing  36* total.  Similar build in a 440.

[frederick]

Thanks guys.

I'd say you need to up your initial timing. What method did you use to determine 13 degrees was what you needed?

I got that from this page:
http://www.diamondbackengines.com/technical-white-papers/ignition-101/
It suggests 10-12 degrees of advance for 220 or less @0.050 cam duration and 14-16* for 221-240@0.050

I've got 220@0.050 so went with 13deg BTDC.
Don't want to go much higher with 9.7:1 compression and no squish.
Hooked up the vacuum advance to manifold, so it's pulling more than that at idle, but haven't checked how much.

The Edelbrocks don't have a secondary throttle stop, but I might be able to make one to get the transition slot squared.
It's not even close to square at the moment, probable the main cause of it holding back just of idle.
Another option I've heard of, like you suggested, would be to drill a small hole in the primary throttle discs, but I don't want to go there yet.

You should be able to drop the vacuum below 10" anytime you want. 1.5" WOT at 3000  RPM is too much too soon.
With an assistant flooring the car do both pri/sec open all the way?
Run about 24* timing  36* total.  Similar build in a 440.

I can drop below 10" but it takes almost full throttle.
Yes, the assistant was flooring it all the way when I did the WOT test at 3000rpm.
Primaries and secondaries are open all the way with the pedal floored.
That much advance?!
It's already pinging at 13*, maybe when I get the right mixture at the right time I can try and go higher on the mechanical advance at idle.

Did some runs with rods which are leaner at cruise and the 8"Hg springs.
Now it cruises with an AFR of 14-15, but it pings when you accelerate hard(but not WOT) and don't go below 8"Hg.
Ping is gone when the power mode of the rods "engages".

So what's next?
-I don't want go back to the original needles and have to cruise at 12.5AFR
So I'm thinking of stretching the 8"Hg springs to have them engage earlier.
Will be some trial and error, of course to get both springs equal.
-Try having the secondaries open slightly at idle and/or try getting more advance from the vacuum advance.
-Getting larger accelerator pump squirters

But I'm strongly thinking about selling the 600 and getting a larger carb.


Cheers,

Frederick

[Manifold]

Thanks guys.

I'd say you need to up your initial timing. What method did you use to determine 13 degrees was what you needed?

I got that from this page:
http://www.diamondbackengines.com/technical-white-papers/ignition-101/
It suggests 10-12 degrees of advance for 220 or less @0.050 cam duration and 14-16* for 221-240@0.050

I've got 220@0.050 so went with 13deg BTDC.
Don't want to go much higher with 9.7:1 compression and no squish.
Hooked up the vacuum advance to manifold, so it's pulling more than that at idle, but haven't checked how much.

Funny you should mention that white paper. The technique I like for determining timing is described in another of their white papers: http://www.diamondbackengines.com/technical-white-papers/vacuum-gauges/

You should be able to make it idle with the 600cfm, but it might be happier with a 750-800cfm.

[firefighter3931]

Hooked up the vacuum advance to manifold, so it's pulling more than that at idle, but haven't checked how much.

That is a problem. With manifold vacuum the distributor will go to retard when you floor the pedal because at WOT vacuum will drop. This will immediately retard your timing. 

Try disconnecting the vacuum advance and dial in the curve with 16-18* at idle & 36* total all in by 3000 and see how it runs.

The fuel curve on that eddy 600 is too conservative for your combo. That Crower HDP271 is a healthy cam, especially in a 383. It may sound mellow but it's a wolf in sheeps clothing and needs to be tuned accordingly. 


Ron

[frederick]

Hi Ron,

Crower 271HDP? I've got a Lunati 60302 camshaft.
Are you suggesting disconnecting the vacuum altogether or changing it to ported?

Manifold, have you tried what it is suggested in the paper, specifically:
Another use is to set your timing curve. Set your timing at idle as explained in the tuning section, check what the timing number is with your light and record it. Now run the engine to the rpm that causes the timing to go as far as it will and repeat the vacuum setting exercise. Check the timing at that rpm and record the number. Before shutting the motor off reset the distributor to the proper idle timing to insure it will start properly when you restart and then shut it down. All of this should be done with the vacuum advance disconnected and plugged if you have it. Now lets look at the numbers.
Let's say your best tune at idle was at 18 degrees, and your best reading was at 36 degrees on high rpm. What that means is you need 18 degrees of total advance on your centrifugal weights.
Won't the high rpm test only work with the engine on a dyno under load?
I would say the high rpm test without any load is good to get the total timing of mechanical + vacuum advance.

Going to look at a 750DP I can get for a very good price tomorrow.


Frederick

[flyinlow]

I have a Lunati 60303 with a 440 should be about the same level of tune as your set up.

Used Waynes tuning video . Advaanced the base timing from 15 to 24* welded the centrifical advance slots to get 12* of crankshaft timing at 2600 rpm.

I did limit the vacuum advance to 8* with ported vacuum above 10" or it pings on light acceleration.

I have a good quenck height with EDDY 84cc heads and SRP pistons so the engine runs on 92 octane gas .

I have a mini starter which cranks the engine over better then the the old style  , on a hot start you can tell the starter is working hard , so I stopped at 24*

[firefighter3931]

Hi Ron,

Crower 271HDP? I've got a Lunati 60302 camshaft.
Are you suggesting disconnecting the vacuum altogether or changing it to ported?

Manifold, have you tried what it is suggested in the paper, specifically:
Another use is to set your timing curve. Set your timing at idle as explained in the tuning section, check what the timing number is with your light and record it. Now run the engine to the rpm that causes the timing to go as far as it will and repeat the vacuum setting exercise. Check the timing at that rpm and record the number. Before shutting the motor off reset the distributor to the proper idle timing to insure it will start properly when you restart and then shut it down. All of this should be done with the vacuum advance disconnected and plugged if you have it. Now lets look at the numbers.
Let's say your best tune at idle was at 18 degrees, and your best reading was at 36 degrees on high rpm. What that means is you need 18 degrees of total advance on your centrifugal weights.
Won't the high rpm test only work with the engine on a dyno under load?
I would say the high rpm test without any load is good to get the total timing of mechanical + vacuum advance.

Going to look at a 750DP I can get for a very good price tomorrow.


Frederick

Sorry Frederick, i thought you had the Crower cam in your 383..my mistake. It specs out almost identical to the #302 (220*) Lunati grind so the engine will behave essentially the same. 

I'm not a fan of vacuum advance but if you absolutely had to have it the ported vacuum is correct. From personal experiece i allways plug off the cannister and tune without it. Unless your engine is making 15* of vacuum at cruise/light throttle, the vac advance unit will not operate properly. I've never had a motor make that much manifold vacuum 


Ron

[frederick]

Don't worry about it, Ron.
I believe there's another 383 on here with that cam.

At least 15"Hg? Well in that case my engine is broderline, it's making 14" at idle and just under 15" when cruising.


Frederick

[Manifold]

Manifold, have you tried what it is suggested in the paper, specifically:
Another use is to set your timing curve. Set your timing at idle as explained in the tuning section, check what the timing number is with your light and record it. Now run the engine to the rpm that causes the timing to go as far as it will and repeat the vacuum setting exercise. Check the timing at that rpm and record the number. Before shutting the motor off reset the distributor to the proper idle timing to insure it will start properly when you restart and then shut it down. All of this should be done with the vacuum advance disconnected and plugged if you have it. Now lets look at the numbers.
Let's say your best tune at idle was at 18 degrees, and your best reading was at 36 degrees on high rpm. What that means is you need 18 degrees of total advance on your centrifugal weights.
Won't the high rpm test only work with the engine on a dyno under load?
I would say the high rpm test without any load is good to get the total timing of mechanical + vacuum advance.

I have used this method. It worked well for me. I can't speak to your questions. Damon (the author) is on many of the Mopar forums (as "Fugly") - don't know if I've seen him here, though. Feel free to hit him up!

[frederick]

Time for an update.

I took off the edelbrock and bought a 750DP.
First impressions are good, it idles much better, idle vacuum has increased to 17"(without touching the distributor), and on the road  it feels like a different engine, much more lively.
And I still have to tune it properly.
So far I've only adjusted the idle screws and decreased the IFR's.

Oh and the off idle stumble is gone.

[firefighter3931]

That's not surprising to hear   

With a more agressive cam you also need more air/fuel. 

The accelerator pumps/squirters are designed to eliminate off idle stumble & lean spots. 

Eddy carbs are notorious for off idle stumble....



Ron