Edelbrock part throttle surge help

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Patrick

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Have a 1405 (600 cfm) on my nearly stock 318 (340 cam and performer intake, 4 speed, 2.9 gear ratio rear. I also welded the dizzy mechanical adv so that i can limit the mech advance and get a little more initial (per posts here on FABO). My total is set to about 32 (i can't remember when initial is but i think i have about 18 mech advance, so ~ 14 initial)

I've completely rebuilt the carb (all stock tuning) and i can get it to idle fine and high power mode seems ok when i step into it. The problem i have is that there is a nasty part throttle (cruise) surge that i'm trying to eliminate. I've richened the mixture to no avail. I also plugged the vacuum advance to see if that was my problem and that didn't help either....

I've read the eddy tuning guide and it sounds like my problem is that i need to bump up the rod to richen the mixture in cruise mode. Part of me doubts that my engine combo would require me to increase the mixture over stock.

Any help would be very appreciated!
 
abody joe did you just adjust the carb or did you have to replace The rod to fatten it up. I have the same surge when cruising I also have an eddy carb. I didn't notice it until I started messing with the timing.
 
i have a holley so i just jetted up on the primary..

340 swing, what is your timing set at? initial and total? i usually like mine in the 17* initial and 35* total range..
 
Thanks Abodyjoe - that's what i'm thinking... i mostly run Holley's but this is my first Eddy so i'm learning how to tune it...

anyone else with specific Eddy experience who would recommend the same thing?

Thanks!
 
Still have the problem... I increased the cruise mixture to the next level from stock keeping everything else the same. It helped a little but i still have a part throttle surge. There is no reason i would need to bump up the mixture more - the motor is near stock! The *only* other thing i can think of is that i'm using the Eddy sp2p emissions 4bbl intake which has small ports - does anyone think that this could be my problem?

I have a spare holley 600 laying around that i rebuilt; i'll throw it one to see if the problem persists and keep you posted if anyone cares. If the problem persists, i may upgrade to a eddy performer intake.

Thanks for any other suggestions guys!
 
If it's surging it's still lean..!!one step isn't enough...
 
What metering springs are you running,mixture screws are for idle mixture,do you have a vacuum guage?
 
bigdemo1,
i will get back to you with the metering spring color. I bought the eddy calibration kit and bumped up the rod to the next level of richness for part-throttle/cruise. I will also get back to you about the vacuum i have at idle. Yes, i adjusted the mixture screws to max vacuum and these adjustments had no perceivable effect on my surge problem...
 
Update...
Installed a fuel pressure regulator and adjusted pressure to 5.5 lbs at idle. Replaced the metering spring to the 8" one (silver, i believe) and neither of these affected the part throttle surge problem. I also disconnected the vacuum advance with no effect either.

When i check timing advance, the timing increases nice and smoothly as i increase the engine speed, so my mechanical advance doesn't appear to be a problem. Would too much initial cause this problem maybe???? I need to check it again (!) but my recollection is that i have ~15 initial, ~15-18 mechanical (i welded the advance plates).... Running out of ideas guys!!!!!! HAHA I've never had trouble tuning Holley's so this is getting frustrating.... Give me some more ideas before i ditch the carb and slap a spare Holley 1850 on there! Thanks in advance...
 
Edelbrock / Carter AFB Setup

EDELBROCK / CARTER SETUP

Ok – here we go – first some general rules and then some more specific tips. BTW my sense of humor may offend some …I accept no responsibility for mental anguish….

GENERAL RULES
1) DO NOT TAKE IT OUT OF THE BOX , TEAR IT DOWN AND MAKE IT BETTER!! But you say "I think it needs to be richer , leaner, ETC" -WHY??? …many, many years of hard work by engineers versed in the product they produce have gone into this design, and chances are they know better than you or your buddy Mr Carb Guru (hereinafter referred to as CG) what works. My racecar is jetted one size bigger all around than the carb came from the factory-not too many engines will have a more radical cam or more messed up signal than this, so don't go putting bigger jets in "JUS BECUZ' "

2) Insure you don't over torque the hold downs- if your gasket is worn out or your intake top looks like the side of a wrecked dump truck -fix it first…

3) If you car /truck /tank /boat etc ran like crap with the old carb and it runs like crap with the new carb….it's probably not the carb.

4) Get the proper carb for your vehicle- undersized carbs, while great for response will be dead at the top end, run richer as a rule (excess velocity causes main circuits to come in wrong) and usually get worse mileage. Oversize carbs (especially vacuum / air secondary type) will have an untunable low end bog, lazy acceleration and nearly impossible idle problems. Somewhere in between is what we are looking for. A simple equation to get you close : ((Max rpm X CID) / 3456 )X V1. V1 is a variable representing the efficiency of your engine . Use .85 for a normal street engine, 1.00 for a fairly stout street engine ( we're talking close to strip car here) 1.2 for a highly modified strip only vehicle. (Yes< I know these are not the same numbers as some books show, but they work for these carbs) BE HONEST (you don't have to tell anybody) -along those lines do not use 7600 for the rpm on your hydraulic cam 8.5:1 street engine.

EXAMPLE: 440, hydraulic street , 5800 max rpm. ((5800 X 440)/3456) X .85 or ((2552000)/ 3456) X .85 or 738 X .85=627 or a 625 440, 620 lift mechanical, 6800 rpm max ((6800X440)/3456) X 1.00 or ((2992000)/3456) X1.00 or 865 X 1.00=865 or 800 (biggest) or 2 X 500

SEE how much difference it makes?

Typically, you can get away with 1 size bigger / smaller eg a 750 will probably be fine on you stock 440 &#8230;but you say " CG said his likes a dominator"&#8230;.does that mean it truly works in an optimum manner?? If you have a high stall converter, 4 speed , don't care about mileage/ drivability&#8230;. by all means put the biggest thing you can find on it&#8230;.

5) Make sure your timing is set /working properly- not enough initial timing /too slow of a curve will cause bogging, while too much total advance will cause your ride to do the "Herky Jerky "down the freeway and or ping. If you can't get a decent cruise rpm after following the below, try disconnecting and plugging the vac advance on your distributor- if it's better, you probably need to get it recurved&#8230;..this is another subject&#8230;suffice it to say, most late model stock distributors have too long an advance curve built in and need to be welded up for performance use&#8230;.

Now on to putting 'er on:

Before you bolt it on- flip it over and make sure the secondaries open all the way when you twist the throttle all the way open. Many times you will find they are only 90-95% open. If you look at the side opposite the throttle linkage, on the secondary shaft, there is a small tang which stops the blades at a specific point. Bend this GENTLY with a set of pliers to allow full opening. It doesn't take much, so don't use your biggest pipe wrench. Now back the idle speed screw (the one on the side of the carb that controls the throttle linkage) all the way out until the blades (primary) don't move any more. Look under the carb now&#8230;.open the primaries -see the little vertical slots? this is the transition circuit. Screw the speed adjustment back in until it holds the blades at the very bottom edge of these without exposing them-this should be close enough to start the car. On the front now- the two idle mixture screws-screw these all the way in (GENTLY-you can use your fingers) and back out about 2 turns. By the way the drivers side vacuum port is full time and the passenger side is ported-usually the distributor will like ported&#8230;.Bolt it on the car now&#8230;.(turn it right side up if you haven't already)

Check for leaks and fire it up. WARM IT UP before you start adjusting things&#8230;.adjust the idle speed screw to get an idle , steady but not too fast. Now adjust the mixture screws to get the fastest smooth idle -go back and forth until you get the best setting. You should be able to turn the speed setting down a bit as you go. Now turn it off and gently screw the mixture screws in all the way while counting the turns. They should be even and somewhere between 1 1/2 and 2 1/2 turns out. Put them back where they were when you finish checking. If they are less than 1 1/2 turns, you have the wrong springs in the metering rods or it's too rich, or the choke is not wide open-check it first- if it's not fully open when the car is warm, loosen the screws and adjust it for full opening with a very slight positive pressure and retune as before. If they are open more than 2 1/2 turns , you are too lean, or have the wrong springs.

CHECKING THE SPRINGS- This seems to really confuse people, especially those familiar with Holleys. These springs and rods control the power mixture- VERY similar to the Holley power valve. The lighter the spring, the faster , or lower vacuum level they close at . Manifold vacuum controls them-at a high vacuum( idle or cruise) they are held closed by the vacuum. When vacuum drops sufficiently, the spring overpowers it and opens, or raises the rod. The tip of the rod is smaller and therefore richens the mixture. The trick is to have them closed at idle and cruise, and open as soon as the vacuum drops signaling more load. Most performance engines seem to like the orange spring or one close to it. To check it requires a helper. I AM NOT RESPONSIBLE FOR YOU RUNNING OVER YOURSELF-WITH OR WITHOUT HELP!! Here is a way to check it and get close without 246 trips around the block. Unscrew the metering rod covers just enough to turn the covers-turn them to expose about half of the little piston and retighten the screws enough to keep the lids from rattling around.-GENTLY-or you will bend the covers. Start the car -see the little pistons go down? Now have your helper put it in gear (brakes on) &#8211; do they stay down? If not, you need lighter springs until they do. To change them, unscrew the plates and remove the pistons and rods-the spring is under the pistons-a magnet or small screwdriver will get them out. Put the next lightest spring in and try again until they stay down. Now comes the fun (dangerous) part-repeat the test only this time have your helper gun the car hard enough to hit the stall speed and let off quickly- make sure your hood doesn't slam you in the head- watch the piston as he lets off- it should jump up and return down&#8230;if it doesn't go a little heavier on the spring- if you are out of options, stretch the ones in there just a little bit. Now return to the tuning part above.

Accelerator pump- Usually shipped in the middle hole&#8230; usually works just fine right there. If the car goes a little, bogs and goes again, move the rod out one hole and try again&#8230;if it bogs and then goes move it in one hole&#8230; this is all done after the previous tuning and assumes your timing is correct.

What to do if it's too rich /lean- If drag testing shows it to be good everywhere but at idle, go to one size bigger rod on the big step- The numbers are generally 7147 or something similar. The first 2 numbers are idle and the last two are power step.( 7147 = 71 idle ,47 power) In the case of just needing idle adjustment go to say a 7347 . You can also use these to tune minor all around deficiencies. EG- 7147 start rod- 7355 to go leaner everywhere. You may have noticed you go up to lean, down to richen-this is because the rod is a restriction. While on this note, going up or down 2 numbers on the rods is not the same as 2 numbers on the jets. You must figure cross sectional area to find the percent of change you made. Unscrew the accelerator arm and set aside ( by the way, when you re-assemble the little link should look like an S, not a Z from the front), unhook the choke linkage and remove the metering rods /springs. Take the lid screws out and remove the top. The primary jets are in the floor of the carb below the metering rod holes and the secondaries are on the floor under the slosh plates behind the floats- the slosh plates lift straight out- sometimes they are tight and need to be pulled out with pliers. Go one size up or down all around, and repeat the above tuning. ALSO- the jets are always bigger in the front on these carbs because of the metering rod restriction- NEVER EVER EVER will the backs be bigger. The backs are typically 3-5 numbers smaller -EG 113 pri / 110 sec &#8230;.
 
I take it this problem got.solved? This funky carb has me all messed up. it ran.fine last year. I rebuilt the engine with new heads, flat top pistons,I beam rods, and a comp he268 cam, Edelbrock performer. I found rust in my fuel system so I rebuilt the carb all stock, replaced my fuel system and started it up to drive finally and it's surging at light throttle. Never had this problem before!
 
Edelbrock / Carter AFB Setup

EDELBROCK / CARTER SETUP

Ok – here we go – first some general rules and then some more specific tips. BTW my sense of humor may offend some …I accept no responsibility for mental anguish….

GENERAL RULES
1) DO NOT TAKE IT OUT OF THE BOX , TEAR IT DOWN AND MAKE IT BETTER!! But you say "I think it needs to be richer , leaner, ETC" -WHY??? …many, many years of hard work by engineers versed in the product they produce have gone into this design, and chances are they know better than you or your buddy Mr Carb Guru (hereinafter referred to as CG) what works. My racecar is jetted one size bigger all around than the carb came from the factory-not too many engines will have a more radical cam or more messed up signal than this, so don't go putting bigger jets in "JUS BECUZ' "

2) Insure you don't over torque the hold downs- if your gasket is worn out or your intake top looks like the side of a wrecked dump truck -fix it first…

3) If you car /truck /tank /boat etc ran like crap with the old carb and it runs like crap with the new carb….it's probably not the carb.

4) Get the proper carb for your vehicle- undersized carbs, while great for response will be dead at the top end, run richer as a rule (excess velocity causes main circuits to come in wrong) and usually get worse mileage. Oversize carbs (especially vacuum / air secondary type) will have an untunable low end bog, lazy acceleration and nearly impossible idle problems. Somewhere in between is what we are looking for. A simple equation to get you close : ((Max rpm X CID) / 3456 )X V1. V1 is a variable representing the efficiency of your engine . Use .85 for a normal street engine, 1.00 for a fairly stout street engine ( we're talking close to strip car here) 1.2 for a highly modified strip only vehicle. (Yes< I know these are not the same numbers as some books show, but they work for these carbs) BE HONEST (you don't have to tell anybody) -along those lines do not use 7600 for the rpm on your hydraulic cam 8.5:1 street engine.

EXAMPLE: 440, hydraulic street , 5800 max rpm. ((5800 X 440)/3456) X .85 or ((2552000)/ 3456) X .85 or 738 X .85=627 or a 625 440, 620 lift mechanical, 6800 rpm max ((6800X440)/3456) X 1.00 or ((2992000)/3456) X1.00 or 865 X 1.00=865 or 800 (biggest) or 2 X 500

SEE how much difference it makes?

Typically, you can get away with 1 size bigger / smaller eg a 750 will probably be fine on you stock 440 …but you say " CG said his likes a dominator"….does that mean it truly works in an optimum manner?? If you have a high stall converter, 4 speed , don't care about mileage/ drivability…. by all means put the biggest thing you can find on it….

5) Make sure your timing is set /working properly- not enough initial timing /too slow of a curve will cause bogging, while too much total advance will cause your ride to do the "Herky Jerky "down the freeway and or ping. If you can't get a decent cruise rpm after following the below, try disconnecting and plugging the vac advance on your distributor- if it's better, you probably need to get it recurved…..this is another subject…suffice it to say, most late model stock distributors have too long an advance curve built in and need to be welded up for performance use….

Now on to putting 'er on:

Before you bolt it on- flip it over and make sure the secondaries open all the way when you twist the throttle all the way open. Many times you will find they are only 90-95% open. If you look at the side opposite the throttle linkage, on the secondary shaft, there is a small tang which stops the blades at a specific point. Bend this GENTLY with a set of pliers to allow full opening. It doesn't take much, so don't use your biggest pipe wrench. Now back the idle speed screw (the one on the side of the carb that controls the throttle linkage) all the way out until the blades (primary) don't move any more. Look under the carb now….open the primaries -see the little vertical slots? this is the transition circuit. Screw the speed adjustment back in until it holds the blades at the very bottom edge of these without exposing them-this should be close enough to start the car. On the front now- the two idle mixture screws-screw these all the way in (GENTLY-you can use your fingers) and back out about 2 turns. By the way the drivers side vacuum port is full time and the passenger side is ported-usually the distributor will like ported….Bolt it on the car now….(turn it right side up if you haven't already)

Check for leaks and fire it up. WARM IT UP before you start adjusting things….adjust the idle speed screw to get an idle , steady but not too fast. Now adjust the mixture screws to get the fastest smooth idle -go back and forth until you get the best setting. You should be able to turn the speed setting down a bit as you go. Now turn it off and gently screw the mixture screws in all the way while counting the turns. They should be even and somewhere between 1 1/2 and 2 1/2 turns out. Put them back where they were when you finish checking. If they are less than 1 1/2 turns, you have the wrong springs in the metering rods or it's too rich, or the choke is not wide open-check it first- if it's not fully open when the car is warm, loosen the screws and adjust it for full opening with a very slight positive pressure and retune as before. If they are open more than 2 1/2 turns , you are too lean, or have the wrong springs.

CHECKING THE SPRINGS- This seems to really confuse people, especially those familiar with Holleys. These springs and rods control the power mixture- VERY similar to the Holley power valve. The lighter the spring, the faster , or lower vacuum level they close at . Manifold vacuum controls them-at a high vacuum( idle or cruise) they are held closed by the vacuum. When vacuum drops sufficiently, the spring overpowers it and opens, or raises the rod. The tip of the rod is smaller and therefore richens the mixture. The trick is to have them closed at idle and cruise, and open as soon as the vacuum drops signaling more load. Most performance engines seem to like the orange spring or one close to it. To check it requires a helper. I AM NOT RESPONSIBLE FOR YOU RUNNING OVER YOURSELF-WITH OR WITHOUT HELP!! Here is a way to check it and get close without 246 trips around the block. Unscrew the metering rod covers just enough to turn the covers-turn them to expose about half of the little piston and retighten the screws enough to keep the lids from rattling around.-GENTLY-or you will bend the covers. Start the car -see the little pistons go down? Now have your helper put it in gear (brakes on) – do they stay down? If not, you need lighter springs until they do. To change them, unscrew the plates and remove the pistons and rods-the spring is under the pistons-a magnet or small screwdriver will get them out. Put the next lightest spring in and try again until they stay down. Now comes the fun (dangerous) part-repeat the test only this time have your helper gun the car hard enough to hit the stall speed and let off quickly- make sure your hood doesn't slam you in the head- watch the piston as he lets off- it should jump up and return down…if it doesn't go a little heavier on the spring- if you are out of options, stretch the ones in there just a little bit. Now return to the tuning part above.

Accelerator pump- Usually shipped in the middle hole… usually works just fine right there. If the car goes a little, bogs and goes again, move the rod out one hole and try again…if it bogs and then goes move it in one hole… this is all done after the previous tuning and assumes your timing is correct.

What to do if it's too rich /lean- If drag testing shows it to be good everywhere but at idle, go to one size bigger rod on the big step- The numbers are generally 7147 or something similar. The first 2 numbers are idle and the last two are power step.( 7147 = 71 idle ,47 power) In the case of just needing idle adjustment go to say a 7347 . You can also use these to tune minor all around deficiencies. EG- 7147 start rod- 7355 to go leaner everywhere. You may have noticed you go up to lean, down to richen-this is because the rod is a restriction. While on this note, going up or down 2 numbers on the rods is not the same as 2 numbers on the jets. You must figure cross sectional area to find the percent of change you made. Unscrew the accelerator arm and set aside ( by the way, when you re-assemble the little link should look like an S, not a Z from the front), unhook the choke linkage and remove the metering rods /springs. Take the lid screws out and remove the top. The primary jets are in the floor of the carb below the metering rod holes and the secondaries are on the floor under the slosh plates behind the floats- the slosh plates lift straight out- sometimes they are tight and need to be pulled out with pliers. Go one size up or down all around, and repeat the above tuning. ALSO- the jets are always bigger in the front on these carbs because of the metering rod restriction- NEVER EVER EVER will the backs be bigger. The backs are typically 3-5 numbers smaller -EG 113 pri / 110 sec ….
Great info, should be a sticky. MT:cheers:
 
Stock is 7/16 I thought. That's where I set it via my instructions. I also. Checked for vacuum leaks around the base plate all hoses and the throttle shafts. I didn't find any. I'm going to have to buy the tuning kit for this carb. It's too bad. This carb is super simple that's why I like it so much, but I hate these little problems.
 
ok i am thinking of the AFB on stock chrysler big block. sorry. but the 5/16 does work. i had a 1965 300 L 413 stock AFB. the plugs was a little lean. so i bumped the float level to 5/16. then the plugs looked very good. i tried the 5/16 cause i had a bunch of spec sheets for the AFB on many diff engines. and they showed several diff levels. so i thought i could try a small change. and on the old AFBs they had some floats with a ribbed side and some with smooth side. each having a diff level. but cant remember what the diff was.
 
You put a cam in it right? and the idle /low speed vacuum dropped right? And the metering rods are held down by vacuum pulling against spring pressure, right?
And the new cam needs a new timing curve.
Well, start with giving the engine the idle timing it wants.This will bring the idle/low speed vacuum up. Perhaps enough to keep the MRpistons down. If not, the answer will probably be in, Post 13.Its a very fine post.
The 268 cam is easy to tune for, so hang in there.
Messing with the float level, I would consider much later in the tuning game. Jumping from 7/32 to 10/32, is a pretty big jump.
Timing is always number 1. Well, actually no 2. First would be mechanical. Making sure the compression is even and adequate, and that the valves are sealing.Especially the intakes.
 
I'm thinking I need stiffer springs in the metering piston. I'm.pretty sure It's running lean, if i spray fuel with a spray bottle into the carb at light throttle it smooths out and runs fine. As soon as I stop it starts to stumble and miss. I'm gonna get a timing light on it and double check my initial.
AJ, don't you think.It would run rich with this 268 cam? I thought it made less vacuum than a stock cam? If it makes less vacuum wouldn't the springs act stiffer so to speak?
 
Those springs are kinda like the Holley PV.The metering rods have to stay down at idle and very low throttle/load settings,and the rods have to supply the correct amount of fuel while stuck down in the jets for this.
Then at very large throttle/load settings the rods have to be up on the power step, letting max flow occur.
At inbetween settings the spring under the piston has to overcome vacuum and lift the metering rod to a setting that again sets the A/F to what the engine wants.
If the carb was formerly tuned to work with a high vacuum cam, it will have a fairly strong spring that had to overcome the relatively high vacuum. Now with the bigger cam/lower vacuum, that same spring is too powerful for the reduced vacuum and pops up too soon and too high,sending the A/F rich.
But thats a whole different story.The metering rods have to stay down until the engine demands more fuel.
At light throttle/load/cruise settings those rods should be stuck down, and the A/F is set by the clearance between the fat-step and the jet.If youre lean there simply swap to a smaller rod.Unless the A/F goes lean on the powerstep too.Then a larger jet would be called for, to solve both lean problems.
I thought the above article went into that pretty nicely.
Now with the reduced big-cam vacuum idle pull-over gets to be a chore for the engine, actually if you think about it from the angle of airflow;atmospheric pressure isnt pushing as hard into the engine, and so isnt pushing much fuel. So the A/F goes lean.At least until the cam starts making vacuum, which with the 268* is delayed to in-the-neighborhood of 1800rpm.if the timing is right.
So to recap 1) mechanical(make sure the intakes are sealing), and 2) get the timing dialed in,(with more advance comes higher vacuum numbers, which helps stabilize the powerpistons),then 3)tune the A/F. I have done in different orders, which always lead me in circles,and totally wasted my time.Well not totally-totally. I did learn how not to do it.
To answer your last question and marry the others to it; I suspect you need a softer spring to keep the rods down a bit longer, and rods with a smaller idlestep, to provide more lowspeed fuel.Since vacuum is likely reduced all the way to 1800ish and your new cam will make more torque, after that, it will probably want more fuel under power as well. To solve both issues, I would leave the rods in for a bit and instead, go up a size on the MJs .
What I like to do is tune the primaries, by defeating the secondaries.This saves time in the long run. Sometimes the primaries are too fat and confuse the power tuning.Plus with the progressive linkage it can be a tuning handful.
 
Your advice, paired with the excellent write up in post 13, helps out a bunch. Like I said, I will buy a tuning kit and will start with the timing and a vacuum gauge.
 
I just fixed my surging problem, turns out is was the vent for the gas tank. Might check that. If you have the charcoal canister there is a check valve in the vent line that can get stuck.
 
you have a lean idle circuit. the fix is to drill the idle jet. easy to do IF you know how. the size is around .032-.036. drill only .001 or .002 at a time. if dont know how you can damage the jet.
 
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