Edelbrock carbs Carter AFB LS tuning.


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Nov 3, 2010
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I say LS tuning as I had to tune my old carb on one but these steps may help others with issues on their non LS engines.

So little information on these carbs it is silly.
I suppose if you dig through the internet enough you can find some tweaks.
Many people speak of the Edelbog they get with their carbs.

A lot of that I have cured with heavier step up springs.
Blue is 3" Hg.
Yellow 4" .
Orange 5".
Pink 7".
Silver 8".

Now sometimes you need stiffer than what is offered in the Edelbrock kits to make the transition from cruise to power come in quicker.
I have added many times a smaller spring inside of the factory spring.
I usually get the smaller spring from a clicker type ink pen.

I feel there could be a market for some springs in the 10" Hg to 15" area

Yes 15" Recently tweaking on a friends just installed 6.0 LS carbureted engine checking vacuum and having 21" of vacuum and cold air gap intake makes that engine want the power circuit to come in very quickly.
Dropping from 21" vacuum to 8" and waiting on power mode to come in is brutal in the bog department.

Which leads me to another issue with these style Edelbrock performer carbs.
Idle feed restriction size.
No idea the size and not an easy thing to change like on a Holley type carb.

I do know for a fact the 750 cfm comes into the main circuit (fuel coming out of the primary boosters) way later than the 600 cfm version.
You have a bog when you stick your foot into it that you can't tune out with the 750 you assume the carburetor is too large.

When in fact it is in the transition circuit.
Yes the 600 will probably not bog like the 750 but do you loose power up top. I have lost power up top every time with the 600.

Tuning this LS carbed thing yesterday in the hot 23 Fahrenheit air with his 160 thermostat was a chore with the #1407 750 cfm Edelbrock carb.

This carb I had on my 385 stroker sbc with flat tops and 58cc heads that are ported 601's with 1.84-1.50 valves 170cc runners RPM intake with 1" spacer.
Carb jetting was 107 primaries with 113 secondaries and 71-37 metering rods with Orange 5" Hg spring. 280 magnum hydraulic flat tappet cam lakster headers and 2.25 exhaust.

No bog on that deal and Air Fuel Ratio was 15.? idle and 14.5 part throttle cruise and 13.? at full throttle.

Not bad really.

On this factory 6.0 from a Cadillac with RPM intake and headers with 3" exhaust the same carb was super BOG. Putting the throttle to the floor slower and from higher R's would lay down until the power mode came in.

Step up springs were used first.. helped some then made them stiffer by adding spring inside of springs. That helped but not the cure all.
Changed metering rods to 65-47 from the 71-37 thinking the jump up in part throttle fuel may help.

It helped the bog/stumble just a wee bit but lost considerable power in the mid range and a lot on top end.
This thing wants fuel.
I pulled the carb.. Well had my buddy pull it as it's his baby not mine.

Pulled the top off and stuck 116 primary jets into the carb it had 107 in the primary and stuck the 107 into the rear which had 113 jets in them.

Installed the longer 1470 accelerator pump and used the top hole on the pump arm.. this will give a longer pump shot.
Slightly raised the fuel level like 1/32 inch.
With carburetor air horn upside down the floats were slightly angled up (remember it is upside down) at the nose in the stock form.. I set them level.
I installed the 71-37 rods back into it.

Time for testing again once the carb is back on the 1" spacer..yes 1" spacer.
Bog was almost totally gone but not all the way.
This thing now pulls harder everywhere.
From a roll at 15 MPH after it cleared up from a bog before it would spin tires for maybe 10 feet.

Now tiny bog and roast the tires for 100 feet and keep you pinned back in the truck bench seat pretty good for an almost stock LS engine [Broken External Image]

This is in a long bed early 70's Chevy truck like 1974 with TH350 and Holeshot 3000 converter.
Full length headers 3" exhaust through old 3" warlock mufflers dumped at the rear end.

He said rear gears in the 340 area..I have not checked them.

I think some Idle feed restriction tweaks or primary booster swapping may happen next.
But waiting for a 60 degree day before any more tweaks are done.

One thing I hate about the LS is the controller that does not tell you the exact timing curve.
just gives you a dial to turn to different settings.. This is the newest MSD unit.
No timing marks on the LS?
Don't love that at all..I think it needs more initial timing and quicker curve in my book.

But for something my friend did himself it is a huge performance gain over the 350" 4 barrel that was pulled from this truck.
Took him a couple months but he got it done and only needed a little bit of help.
I told him I was not holding his hand on this deal and traded him the 1407 carb for the 350 that came from the truck. as he wanted that carb.


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Friend brought over his Chevelle Pro street with the 31x18.5 tires and 489" BBC
Pro comp 320cc heads with [email protected] .050 camshaft 2500 stall 12" converter Yea that is what I said.

Anyway he has the dual 4 tunnel-ram tall one and 2 750 edelbrock #1407 carbs ..10.5 compression. 100 octane and a lot of nitrous.

Now he did not run it with nitrous as I told him bring it to me and I will tune it .

It was all stock inside the carbs.
Major bog off idle and even at 3000 rpm punch it and stumble and carry on.
He thought it was rich as plugs were black.
Fresh build less than 50 miles..cold plugs also.
Changed plugs to 1 step hotter.

Checked too see if metering rods stayed down at idle?
Do they bounce up quick when you tip the throttle ?

Swapped the orange spring to silver and they stay down at idle and instantly jump up.
Test drive.----Way better zero stumble.
2 changes.

I felt some shudder I thought it was tire shake but it felt different.

Got back home pulled a couple plugs.. white and clean.
Replaced 71-47 rods with 65-37 rods.

No more shudder and much more throttle response and more power .
I told him go add more jet and see if it likes it as plugs are still snow white.

OK this is what got me. BBC rectangular port heads 2.25-1.88 valves 320cc runners and the low too me compression (cranking psi 165)
262-272 @ .050. Tight lash Solid roller.
I was thinking sluggish off the line .
NOT AT ALL blip the throttle at 1500 and and it responds like a motorcycle engine, instant revs.

I stuck a [email protected] .050 in a 355" and expected saggy bottom end but it revved like a KZ1000.

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