Edelbrock 750 tuning - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 04-02-2008, 06:00 PM
Registered User
 
Join Date: Nov 2005
Location: CT
Posts: 195
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Edelbrock 750 tuning

I did a search on the usual questions for the Edelbrock carbs. My car is a '62 Corvette, '70 LT-1 shortblock, Dart Iron Eagle Platinum heads (200) running about 10 to 1 comp. HEI distributor, 36 degrees total, headers, Torker manifold, new Edelbrock 1407 carb.

The car still has a bog from a stop. I went one notch on the pump linkage and went to the third notch, but haven't driven it as yet. With revs up it seems fine and from 2,000 rpm up it's quite strong. It seems to be running a little lean as plugs are more white than tan. I have the tuning kit with metering rods, jets and springs. I'm a little confused on the springs. The carb comes with the orange #5 springs. Which springs should I try to make it run a little richer when first starting to accelerate. Also I'm a little confused on the meaning of Cruise Mode and Power Mode and which is affecting the bog and rpm under 2,000.

    Advertisement

Last edited by GCD1962; 04-02-2008 at 06:17 PM.
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 04-02-2008, 06:25 PM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,153
Wiki Edits: 0

Thanks: 5
Thanked 380 Times in 374 Posts
You can solve 99% of your tuning and drivability issues ("off idle bog") by simply replacing the outdated torker manifold with a modern dual plane hi rise intake manifold.
if you can fit it under the hood (with a corvette drop base aircleaner) use a Edelbrock Performer RPM manifold . If not, A mid rise Edelbrock Performer "EPS" or a Weiand Stealth #8016 low rise dual plane manifold will fit. Once you've done this you can dial in the part throttle cruise circuit of the carb by swapping the primary metering rods to a #7547 pair
#7147 rod pair is stock.
The edelbrock carbs tend to want a lot (more) of initial spark advance at idle.
You need to recurve your distributor mechanical advance curve, especially if you have a larger than stock cam in the motor. More initial at idle+ less mechanical advance travel +34-36deg total timing at high rpm WOT.

You'll never completely get rid of the off idle bog at low rpm of a torker manifold. the cylinder to cylinder fuel distribution at low rpm near idle sucks.
The cure is to replace the intake manifold with a dual plane intake manifold.
You'll like the way the car drives overall a lot lot better.
A modern dual plane hi rise will make more power at all points inthe rpm range than the old torker.
What cam is in this motor?

Last edited by F-BIRD'88; 04-02-2008 at 06:33 PM.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 04-02-2008, 06:38 PM
Registered User
 
Join Date: Nov 2005
Location: CT
Posts: 195
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Appreciate the comments on the manifold. None of the other Edelbrocks fit a '62 even with a dropped base air cleaner. I have a Weiand Stealth but it is not port matched and the ports are quite small compared to the ports on the heads. I have been running the Torker for over 15 years, but had a Holley 750 and never a bog problem. I am running a good amount of advance. 10 degree initial without the vac advance hooked up. Almost 25 degrees with it hooked up and is all in at around 2,200 rpm. I'm pretty sure if I can get a few more minor adjustments it will be ok as it seems almost there. I'll change the metering rods as suggested if the positioning of the accell pump rod doesn't solve the problem. Cam in the motor is the stock LT-1 solid lifter cam. At idle I have around 13-14 hg
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 04-02-2008, 06:50 PM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,153
Wiki Edits: 0

Thanks: 5
Thanked 380 Times in 374 Posts
you need a lot more static initial advance at idle with that cam.
18 to 24 at idle static +12 to 18deg mechanical, in by 3000 rpm for 36total.
add to that 12-15deg of ported vacuum advance.
The throttle response and idle quality will be much better.

A GM Corvette L-72 L-88 BBC drop base air cleaner will give you 1 more additional inch of hood clearance than the typical aftermarket drop base will.

it is the lowest hugging, best shaped aircleaner base made.
Attached Thumbnails
Click image for larger version

Name:	L88basecc.jpg
Views:	7197
Size:	9.8 KB
ID:	29005  
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 04-02-2008, 06:52 PM
Registered User
 
Join Date: Mar 2008
Location: okla. usa
Posts: 42
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
go to the pink lift springs on the metering rods.

If that does not fix it call Edel...you need a bigger accel. squiter nozzle...
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 04-02-2008, 06:53 PM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,153
Wiki Edits: 0

Thanks: 5
Thanked 380 Times in 374 Posts
Which LT-1 cam are you using. the older 1969-early 1970 version .485"-.485" 30-30 lash "346" "30-30 cam" or the revised 1971+ version. .455"-.485" .024-.28" lash.?
"178" cam

the torker manifold always did have a off idle problem. the holley carb may have been better,but if you swap the manifold for your stealth manifold, you'll really see the difference. is this a automantic or a 4 speed car?

Edelbrock tuning
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 04-02-2008, 07:01 PM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,153
Wiki Edits: 0

Thanks: 5
Thanked 380 Times in 374 Posts
as it seems almost there.

Exactly my point. You can tune and tune and tune and you'll never get it right cause the torker manifold sucks at low speed below 2000rpm. Always did, always will. that feel that it is just not quite right will always be there.

As soon as you change the manifold, you will see what I mean.
The old Weiand stealth 8016 is a nice street manifold. I would get busy with the die grinder and get it port matched and bolt it on.

if you want to bang your head against the wall for a bit more try a Brodix "turtle" in the manifold plenum.
Brodix Turtle
A tunnel ram has better drivability, than the old torker manifold.

Some things from the '70's are better left in the '70's.

Last edited by F-BIRD'88; 04-02-2008 at 08:03 PM.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 04-03-2008, 08:26 PM
Registered User
 
Join Date: Nov 2005
Location: CT
Posts: 195
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by F-BIRD'88
Which LT-1 cam are you using. the older 1969-early 1970 version .485"-.485" 30-30 lash "346" "30-30 cam" or the revised 1971+ version. .455"-.485" .024-.28" lash.?
"178" cam

the torker manifold always did have a off idle problem. the holley carb may have been better,but if you swap the manifold for your stealth manifold, you'll really see the difference. is this a automantic or a 4 speed car?

Edelbrock tuning

The older '69-'70 version. Came with the short block right from GM. It's a 4-speed in a '62 Vette, so not a real heavy car.
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 04-03-2008, 09:33 PM
carsavvycook's Avatar
My 2 cents worth
 
Last photo:
Join Date: Sep 2007
Location: Lakeside, CA
Age: 57
Posts: 2,855
Wiki Edits: 3

Thanks: 2
Thanked 2 Times in 2 Posts
FBird did you not meen they come with 7547 metering rods and replace them with 7147 rods? This would richen it up in the lower power range.
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 04-04-2008, 09:28 AM
Member
 
Last photo:
Join Date: Nov 2004
Location: Lakeland FL
Age: 65
Posts: 4,110
Wiki Edits: 0

Thanks: 0
Thanked 3 Times in 3 Posts
I do agree with F-bird....
maybe explaining it in a different way will help...

preface:
the 13-14Hg at idle honestly tells you next to nothing for drivability..the Edelbrock carb has a "independent" idle circuit which is tuned with the blades closed.. versus.... the Holly which can have the blades open a bit...

at around 1400rpms, the Edelbrock transitions over to work on the actual primaries fuel supply and at that point... with very little timing in the motor... there is next to no Hg to make even a crummy A/F mix suspension so the carb is feeding "liquid" gas into the cylinders which makes "no" power and feels like a "bog" (all because of the carb is a little bit to big and the HUGE intake open plenum area designed to work at minumum 2500rpms)

by increasing the base starting point timing, the motor will make ALOT more Hg at the lower rpms and that means ALOT MORE TQ due to higher A/F velocity to allow the motor to wind up faster....and not bog due to the way to low Hg

simple demo:
at 10*, the guage reads say 13Hg at idle, vac adv plugged, just turn the base up to 18* and read the guage...
probably it will read 16-18HG+...and now the idle is probably 500rpms+ higher without touching the gas mix screws..."why?"... because at 18* base the carb is now making a more "ideal" A/F suspension with 16-18HG at a much higher "velocity" into the chambers...
the idle rpms went up because the "better mix burn" due to more Hg makes alot more power with the same amount of gas (so the motor can better over come the internal motor friction and load)...

the same thing will happen with more starting point timing while actually driving on the primaries...

NO WOT ALLOWED and low rpms light throttle testing only but:
to actually "see" the HG difference the timing change makes...rig up your guage so you can read it while driving.....
with only 10* base, when you step on the gas just normal the guage will likely read only 5-8HG which means there is no vac advance timing being added and the carb is making a very crummy mix...
change the base to 18* and likely the Hg will read (hopefully?) 12-14Hg with just normal gas pedal which means there is some vacuum advance still in the timing and the carb is making atleast a decent A/F suspension

you definitely need to recurve the dist before messing with the carb

re: the "springs"....
are all about the car wt/gears motor load...
(simplest explaination/example I can think of)
"if" you were going to be towing a 30' boat behind your vette with only 3.0 rear gears and be driving up a steep mountain grades...you would want to use a stronger-higher rated spring for "detonation insurance" just driving normal with such a huge load on the motor....

Hg directly reads the "load" on the motor (lowHG=high load)...the stronger spring will lift the rod to the richer fuel mix rod step at a "less load" amount of Hg to prevent ping...
bottem line:
go richer sooner at a higher Hg when towing the boat.... versus... no need for richer till much lower Hg with a weaker spring when "not" towing the boat...

Last edited by red65mustang; 04-04-2008 at 09:58 AM.
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 04-04-2008, 09:55 AM
Registered User
 
Join Date: Nov 2005
Location: CT
Posts: 195
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
RE: Red65Mustang

Thanks for comments. The distributor is a brand new Moroso HEI with 36 degrees total built in. It has an adjustable vac can. I have 10-12 degrees with vac plugged. With it hooked up it reads about 25 degrees with dial back light. I have total advance all in at around 2200 rpm. If I bump initial up to 16-18 degrees with vac plugged, is that too much and what other adjustments should I make, for example would I then adjust the vac can to be all in later, say around 2800 rpm?

I'm still a little confused on the step up springs. To get it richer do I use a stronger spring or weaker spring?

Thanks,
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 04-04-2008, 10:42 AM
carsavvycook's Avatar
My 2 cents worth
 
Last photo:
Join Date: Sep 2007
Location: Lakeside, CA
Age: 57
Posts: 2,855
Wiki Edits: 3

Thanks: 2
Thanked 2 Times in 2 Posts
A stiffer step-up spring will raise the metering rod higher richening it up possibly too much. Your timing should be set pretty good right now the way it is. The adjustable vac advance is for more or less advancement, not sooner or later.

Here is an example of fine tuning a edlebrock carb.

I have a hand held 5 gas analyzer with a air/fuel ratio function. A perfect A/F on it is 1.000 anything below that is rich, and everything above that is lean. The complaint from my customer that owns the Blown 1973 Corvette in my pictures, is popping back through the carbs sometimes when cold. The carbs are set up with 107 jets, 7542 metering rods, and the step-up spring at 8 inches. At full boost it runs perfectly, but in the lower power circuit it's A/F Ratio is 1.222 (lean). So I ordered 7342 metering rods to richen up the lower power circuit only by a little bit, and I figure it"s A/F ratio will be around 1.050, still on the lean side just a little bit. After I install these metering rods I'll post it's actual A/F Ratio it comes up with.
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 04-04-2008, 10:45 AM
Member
 
Last photo:
Join Date: Nov 2004
Location: Lakeland FL
Age: 65
Posts: 4,110
Wiki Edits: 0

Thanks: 0
Thanked 3 Times in 3 Posts
? your mis-reading your dist info

95% of all HEI's have 20* of centrifugal advance capability....

for your dist to show 36*'s ("built in") at only 2200****rpms full centrifugal timing ....the base would "have to be" set at 16* (16base+20centrifugal=36*)

read your total with the light at 10* base above 2200rpms and it will show only 30*

the vac adv can is then adding up to 12* more timing only when the motor is under a light load and the HG is high...

so with 16* base just cruisin' with light throttle at 2200rpms plus the timing total is now 16+20+12=48= pretty normal cruising TT

at 10* base you are only at 42* cruising TT possible and only 30* possible at WOT

****depending on your rear gears and actual car weight...it "may" possibly be able to tolerate full timing at only 2200 and not go "kaboom"....but your cam only wants full timing at closer to 2600-2800rpms...see step one below

re: springs
from my experience, with your set up.... about a 1% chance that changing the springs will help even a tiny bit to solve the bog....
your fighting extremely low HG at low rpms with a load on the motor (which means "NO" low end HP/TQ due to the intake...more base timing is a "partial" fix...
(with a dual plane intake at 2,000 rpms the motor will make close to 300 ft/lbs of TQ "acceleration force" due to much higher Hg and velocity....with more timing to help, the Torker is only making "maybe" 150ft/lbs at 2,000= no acceleration power with a 3,000 lb car)

step one: put atleast one heavier spring in the cent to raise the "all in" rpms...to about 2800
step two: increase the base to 16* and test drive...
step three change the rods to "thinner" (lower numbers) and test drive to see if a bit richer helps (white plugs can possibly be from the gas additives package but more likely it is "cruising" a bit lean)

one you have the timing and basic carb set up fairly close to best..."then" you play with the vac adv adjust to see if it can have a bit better throttle response (and better mpg)

Last edited by red65mustang; 04-04-2008 at 10:52 AM.
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 04-04-2008, 01:33 PM
Member
 
Last photo:
Join Date: Nov 2004
Location: Lakeland FL
Age: 65
Posts: 4,110
Wiki Edits: 0

Thanks: 0
Thanked 3 Times in 3 Posts
GCD,
a footnote:
with those very weak 2200rpms springs in the dist....

they may already be adding some centrifugal degrees when the motor is at idle....

best to turn down the idle to as low as the motor will go (300-400 rpms) and read the base timing there with light springs to know for sure 10* is 10*...

ignore the the totally rough idle at 400..and leave the carb alone....it won't hurt anything while you just check the timing base....

(what "may" be happening is the actual true base timing is actually only say 6* and at 750rpms idle the centrifugal is already adding 4* so you think the base is "10")

do the same when you set it to 16* base....turn the idle way down low to be sure none of the centrifugal is present....

(apology...somehow I ALWAYS forget to post that info!!!! for setting base timing)
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 04-04-2008, 05:19 PM
Registered User
 
Join Date: Nov 2005
Location: CT
Posts: 195
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
The total advance of 36 degrees at 2,200 rpm is a result of the adjustment of the vac can. The adjustment controls the rate of the advance, not the amount of advance as it stops at the same degree level. ie. with the initial advance with vac disconnected and plugged of 10-12 degrees if I increase the rate it will show at idle with the vac connected of approx 25 degrees and reaches total at 2,200 rpm. If I slow down the rate, it will read about 18-20 degrees at idle with the vac connected and reaches total at approx 3,000 rpm, and so on. The springs in the distributor are the medium strength ones that give the total advance of 36 degrees.

I can not slow down the idle too much. It is the solid lifter 70 LT-1 cam which has a normal idle of about 900 rpm. I doubt it would even run at 500 or 600 rpm.

I appreciate the help and any other suggestions. I did move the accel pump setting up one more notch, but haven't had a chance to try it as yet (weather not the best around here). From there I will adjust the vac can to get total around 2,800 rpm and bump the initial up to about 16 degrees. and from there if need I'll change to slightly richer rods.

down the road I probably will put on the Weiand Stealth, but it needs to be port matched.
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Tuning tips edelbrock 1406 remi kristiansen Engine 5 10-16-2007 06:48 PM
Edelbrock carb tuning help D. Newland Engine 7 08-31-2007 12:07 PM
Vintage SCB cross ram tuning issues (Edelbrock X C8) 30fordhotrod Engine 13 08-17-2007 07:44 PM
750 cfm carb - tuning - smaller jets or 600cfm? 65truck Engine 8 01-20-2004 06:13 PM
Edelbrock carb tuning Oldsmoblily Engine 4 06-12-2002 06:44 PM


All times are GMT -6. The time now is 04:33 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.