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modifying that too rich edelbrock 1405 carb?

87K views 23 replies 12 participants last post by  DoubleVision 
#1 ·
O.K. before putting this carb in the garbadge as few of you are going to suggest maybe I still can do something with that 600 cfm manual choke edelbrock carb..mayby some experts here could help?

This carb is on my 383 and since day one always had been too rich according an exhaust sensor,rich smell and black sparks..I've done my homeworks checking floats level,idle circuit adjusted decently,checking choke is open all the way,and most important tried about all combinations of jets/metering rods/springs available with no sensible ameliorations.

I was checking today the carb and trying to push open the secondaries plates I realised they offer a surprising resistance. Can it be that this create an air restriction making it a too rich mixture? I know the counterweights can be trimmed down ..should I look into this?

My usual driving is around 2800-3000 RPMs and the vacuum gauge then shows around 20 " HG. I think that is a lot and I kind of think that too much fuel is drawn in an not enough air...should I think about possibly drilling small holes into the primaries plate for more air? The 14X3 extreme air KN filter should not restric nothing here.

I am considering another carb (holley or whatever) but I keep reading so many complaints about too rich carbs. (holleys or whatever again!) that I feel like If I swap my actual edel. for something different all I'd end-up with is a new too rich carb. that I don't know nothing about how to tune (or try to do so!).
Please edelbrock knowledgeable fellows bring in your ideas.
thanks again,Ronald.

P.S. I had the exact same model carb. on a 289 ford with an edelbrock performer and my lugs were perfect tan...?!"/$
 
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#2 ·
You have checked the fuel pressure? If the carb is too rich on a 383 something is wrong with it somewhere. The secondarys have no effect on the primary side. Many (myself included) chased this same problem too long before checking the fuel pressure and fining it was too high. Edel`s don`t like over 5 psi.
 
#3 ·
i've played with an edelbrock 1405 on a mild built ford 302 and found that the factory settings were way too rich too. i just bought a re-jet/re-rod kit for the carb from napa and used this chart to help choose which rods/jets to use. just make adjustments to either and monitor your a/f meter during idle, cruise, and w.o.t.

the chart:
http://www.edelbrock.com/automotive/eps_1405.html

for more information, here's some "light" reading you might consider
the owner's manual:
http://www.edelbrock.com/automotive/eps_intro.html
 
#4 ·
Edelbrock fuel dump

TVR383,DoubleVision is absolutely correct about the fuel pressure.AFB`s do not like pessures above 4-5lbs.Another factor to check is manifold vacuum at idle.Low vacuum camshafts create a need for a revised idle circuit.A 1405 AFB was designed as a basic replacement or a light performance carb.If you have a camshaft with a duration of 220 degrees or more at .050 lift, then you will never be able to correct the rich idle.If your camshaft is under these figures and fuel pressure is correct then start using the tuning guide that came with the carburetor.Good luck from rodderjohn. :cool:
 
#5 ·
rodder john said:
TVR383,DoubleVision is absolutely correct about the fuel pressure.AFB`s do not like pessures above 4-5lbs.Another factor to check is manifold vacuum at idle.Low vacuum camshafts create a need for a revised idle circuit.A 1405 AFB was designed as a basic replacement or a light performance carb.If you have a camshaft with a duration of 220 degrees or more at .050 lift, then you will never be able to correct the rich idle.If your camshaft is under these figures and fuel pressure is correct then start using the tuning guide that came with the carburetor.Good luck from rodderjohn. :cool:
John,

The pressure is kept aound 4-5 via a regulator. My cam is a 230 degrees...when you say the idle circuit will always be too rich with a cam over 220 does it mean I will be too rich at idle speed alone or all over the RPMs range?

According my o2 analyser ( its an old thing that could be done) after fiddling with the idle screws I'm OK at idle,altough it smells rich,but any range beyond shows too rich.BTW what I cannot understand is that trying all jets/rods/springs combos as per edelbrock's instructions (I had bought and tried many a times new jets/rods),even going to LEAN 10 or 12 % combo,my O2 will still indicate too rich ..so do the plugs indicate also! I might have merely ameliorate the O2 readings by one bar.

My sparks plugs after only 500 miles have some hardened black carbon deposits and I don't like the idea of seeing carbon deposits inside my recent rebuild 383. I have seen the oil level going down within the said maiden 500 miles also and cannot be sure if the plugs carbon deposits have been caused by rather the too rich carb. or oil or both!

In any case the apparent too rich case needs to be cared for but after two years now of looking into it (believe me that I have read and tried all edelbrock's pamphlets,etc.) I am just wondering if the carb has not some defects that avoid all tuning efforts!?

thanks,Ronald.
 
#7 ·
Steve karch said:
In some applications having too small of a carb will cause it to run rich as the smaller venturies will create higher velocity and hence draw more fuel from the carb. Going to a 750 cfm of whatever brand may help somewhat.
Steve,

Your comment makes a lot of sense...among all theorical possibilities that came through my mind that exactly one pictured itself in my brain and still does..the problem is how could I check the validity of the theory without having to deal with actually buying,trying a bunch of different brand,size of carbs..an exercise that could just drive me crazier than whatever I am after two years of fiddling with the problem already!
thanks.Ronald
 
#9 ·
TVR383 said:
Steve,

Your comment makes a lot of sense...among all theorical possibilities that came through my mind that exactly one pictured itself in my brain and still does..the problem is how could I check the validity of the theory without having to deal with actually buying,trying a bunch of different brand,size of carbs..an exercise that could just drive me crazier than whatever I am after two years of fiddling with the problem already!
thanks.Ronald
Small carbs don't do this. All they will do is create a better booster signal.

A 230@.050 cam is not to big for a Edie carb

Black and hard deposits are an oil control problem not a carb problem. Bad plugs,(fouled out, not hot enough) will cause similar issue's.
 
#10 ·
are the primaries opened to far in order to maintain idle speed with the lumpy cam?on a holley doing this causes the engine to begin pulling from the main metering ciruit causing rich mixtures. Afix for holley is to drill.125 holes in each primary throttle plate.allowing the plates to be closed back to allow the proper amount of idle slot exposure.
 
#11 ·
agree with johnsongrass....

if you are showing 15+Hg at idle (700rpm?) with the 230 cam then start looking elsewhere......weak spark, cold plugs, timing, cap and rotor, etc.

only 500 miles since the re-build!!! drive it about 2000 miles checking for oil loss......easily can be the rings not seated yet
 
#12 ·
johnsongrass1 said:
Small carbs don't do this. All they will do is create a better booster signal.

A 230@.050 cam is not to big for a Edie carb

Black and hard deposits are an oil control problem not a carb problem. Bad plugs,(fouled out, not hot enough) will cause similar issue's.
I need to make a correction about my cam it is a 220 int. 231 exhst at .050. Plugs are now carbon fouled after 500 miles but were brand new 12Y champion to begin with..can and should I get hotter ones?

About the idle circuit adjustement if I close the screws further in it just won't keep idling good specially when cold where they are now doesn't get gaz sucked in from main circuit..it did but I backed them off.


About the primary plates getting drilled .125 holes..that is what I was thinking first ..my understanding is that would have effect only in closed to almost closed in primary throttle plates allowing extra air but while cruising,partially opened plates at angle what kind of extra air would this allow?

thanks,for the inputs,
Ronald.
 
#14 ·
TVR383 said:
I need to make a correction about my cam it is a 220 int. 231 exhst at .050. Plugs are now carbon fouled after 500 miles but were brand new 12Y champion to begin with..can and should I get hotter ones?

About the idle circuit adjustement if I close the screws further in it just won't keep idling good specially when cold where they are now doesn't get gaz sucked in from main circuit..it did but I backed them off.


About the primary plates getting drilled .125 holes..that is what I was thinking first ..my understanding is that would have effect only in closed to almost closed in primary throttle plates allowing extra air but while cruising, partially opened plates at angle what kind of extra air would this allow?

thanks,for the inputs,
Ronald.
Hard stuff is oil. Soft stuff is fuel. A hotter plug might help but with sucjh few miles you can't say anything yet. The idle mixture screws don't pull from the main circiut ever. You won't pull from the main till around half throttle or a little less. You can't set up a carb to run cold and hot without a choke. Too many compromises are present. When ever doing adjustment's you should drive till full operating temps have been established. This usaully takes about 5 miles or so of constant same speed driving. You don't even haveenough miles on her to worry yet. Get another 1500 or so and make adjustment's to fine tune then. It's quite common to foul a plug while seating the rings. Just clean 'em and go till you get about 2000 miles. Then fine tune. You may even find you have to tinker a little after 5000 miles when things have worn off the new.
 
#15 ·
Steve karch said:
Ronald
What is your initial timing and where do you have your vacuum advance hooked into. Is it ported or manifold vacuum
,,

Steve,
I've put the initial timing at 17/700-800 difficult to be precise as it varies the idle somewhat cause of the cam I guess (among other uncontrolables!). I'm not sure I get right your second question but its a mechanical advance MSD so no vacuum advance here..I get my vacuum readings from a hook up to the carb...
 
#16 ·
johnsongrass1 said:
Hard stuff is oil. Soft stuff is fuel. A hotter plug might help but with sucjh few miles you can't say anything yet.

(((((The idle mixture screws don't pull from the main circiut ever. You won't pull from the main
round half throttle or a little less.)))))))

You can't set up a carb to run cold and hot without a choke. Too many compromises are present. When ever doing adjustment's you should drive till full operating temps have been established. This usaully takes about 5 miles or so of constant same speed driving. You don't even haveenough miles on her to worry yet. Get another 1500 or so and make adjustment's to fine tune then. It's quite common to foul a plug while seating the rings. Just clean 'em and go till you get about 2000 miles. Then fine tune. You may even find you have to tinker a little after 5000 miles when things have worn off the new.
Johnsongrass,

From what I can understand about what you are saying about not actually pulling from the main circuit till just a bit less than half throttle Is from idle till a bit less than half throttle gaz gets in via the idling circuit? If so whatever effort to lean down that carb while cruising at around 60-70 mph (wich I guess is less than half throttle) via rods/jets swapping is useless since these do control the primary or main circuit?

I understand that idling screws mixture work on a separate circuit from the main,I understand that fiddling with idle screws shouldn't agffect the main...didn't (and still ) don't know when the main gets on..you say a bit less than half...

OK lets agree that I need to wait before concluding my engine will need AGAIN to be pulled...another 1500 miles or so. But I'd like to be sure I don't run an overich mixture that could destroy it within the next same 1500 miles!
I'll swap that 20 years old o2 analiser to make sure i have good readings but it stinks rich,both tail pipes are sooty and the plugs..

thanks .
 
#17 ·
I think your timing in is the ball park. The reason I asked on the vacuum advance is if it is hooked into a manifold source that will pick up your idle and by advancing the timing and allows you to back off the base idle and get on the the idle cir cut which helps get rid of a rich idle problem but from what you've said it looks like you've got that sorted out. I still think the carb is too small. You do have to put more miles on this engine and let it break in as others have said. I was constantly adjusting this and that till the engine settled down. I'd do one trip and the the idle would be 100-200 rpm high than before I left. I had an Edelbrock 750 on my 406 and didn't like it. I replaced it with a Holley 750HP DP and have had no problems. Runs great out of the box. Even in colder weather, with no choke it starts better and idles better than the edelbrock. Let 'er rip pal.
 
#18 ·
Don't drill your throttle plates yet! You shouldn't have to do that for a cam of your size. Even if you did need to drill your throttle plate start with a smaller drill. Drilling the throttle plates is for when you have to use excessive throttle opening to maintain idle speed. Adjusting the secondary throttle plates is a more reversable method of getting more idle air when required.
 
#19 · (Edited)
Again, you are wasting your time trying to tune the carb and motor till 2000+ miles

To get to 2000 miles safely with out hurting the motor (detonation from carbon build up): do a compression test now (write down the results), set the total timing (base + mech) to about 32-34 degrees at 3000rpm, do lean out the idle screws, use 92 octane or add octane boost if the C/R is more than 9.0, check the oil every 250 miles. Long highway trips, 2800rpm is best. After 2000 miles test compression again to confirm all is good.

YES it will idle like crap and have no power and probably stink and the tailpipes will be sooty. Forget performance and plugs for now, you need lots of revolutions on all the mechanical parts to know if the motor is good or bad

Reason: you have know for sure and absolutely it is NOT oil consumption due to valve guides, rings, etc..
don't lean the carb jets and rods now! it will make the heads hotter increasing the possibility of detonation during the break in miles.

Post again after 2000 miles and good compression test results, then it's time to tune the timing (17 degree base?) and carb.
 
#20 ·
TVR383 said:
Johnsongrass,

From what I can understand about what you are saying about not actually pulling from the main circuit till just a bit less than half throttle Is from idle till a bit less than half throttle gaz gets in via the idling circuit? If so whatever effort to lean down that carb while cruising at around 60-70 mph (wich I guess is less than half throttle) via rods/jets swapping is useless since these do control the primary or main circuit?

I understand that idling screws mixture work on a separate circuit from the main,I understand that fiddling with idle screws shouldn't agffect the main...didn't (and still ) don't know when the main gets on..you say a bit less than half...

OK lets agree that I need to wait before concluding my engine will need AGAIN to be pulled...another 1500 miles or so. But I'd like to be sure I don't run an overich mixture that could destroy it within the next same 1500 miles!
I'll swap that 20 years old o2 analiser to make sure i have good readings but it stinks rich,both tail pipes are sooty and the plugs..

thanks .
Yep that's right, about 90% of the vehicles out there are running mostly of the idle circuit. Now you must remember that the circuit's do have some overlap. So the further from idle the blades get from a idle position the less you are using the idle circuits and the more main circuit is being used. So, if you are at 1/2 throttle with steady state driving and it's rich you can fine tune with the main or fine tune with the idle circuit's but you won't be making any large adjustment's to either. The more that circuit is being used the more the affect from the change. I hope this makes sense. Running with a vacuum gauge is a god way to decide which circuit is being used. Compare that with with you right foot feel and A/F meter to decide which circuit is needing adjustment's and then how much to adjust. Here's a example

Vacuum high with low foot pressure means 20% main and 80% idle.

Vacuum low with high foot pressure means 90% power circuit and %10 main.

Vacuum near idle vacuum means 90% idle circuit and 10% main.

Vacuum low with low foot pressure means 90% main and 5% idle and 5% main.
 
#21 ·
Johnsongrass1, both the idle circuit and primaries circuits are dependent on the rod size and jet size gas flow volume available (so I ignore the % of which circuit does how much ).

Back to his original question: "how to make it drive/run/cruise leaner?"
Example:
Stock calibration is .0100" primary jet, .070" (high vacuum) rod. .0100"-.070"=.030" opening available for fuel flow
To make it way way leaner for cruise and fuel economy swap to .095" jets in the primarys. .095"-.070"rod= .025" opening for flow.
.025"opening/.030"opening= 17% leaner until the vacuum goes below 5Hg
Assuming the stock calibration was rich (13/1 A/F ratio) the .095" jet will lean it to 15/1 A/F ratio (13A/F ratioX117%=15.2)
The .095 jet will lean the low vacuum/high load (stop signs, hills etc) by 5% (to 13.6/1 A/F with the stock (second number) .042" rod diameter. Want way way way leaner with low vacuum/heavy pedal/heavy load....use the .070" and .052" rod with the .095"jet . 100-42=58, 95-52=43, 43/58= 26% leaner = 13X126%= 16.3/1 A/F

NOTE: This much change is usually "off the chart!" could burn your valves!
I tried to keep it as simple and short as possible, to show the math which applies to any rod/jet size change.
Start with small changes, stock .0100" jet with "fatter" .075" and .047" rod, then maybe a .098 jet with a .073" and .042" rod.
 
#22 ·
Fredma

Steve karch said:
In some applications having too small of a carb will cause it to run rich as the smaller venturies will create higher velocity and hence draw more fuel from the carb. Going to a 750 cfm of whatever brand may help somewhat.
I agree with too small of carb. I have a new zz4 383 crate motor and jegs sent and advised a 850 Edelbrock. At idle it is a little rich but at full throttle runs like a bear . plugs look good, now this is in a 1966 Elco so I dont have all the electronics you have.
 
#23 ·
I know it's been a while— but I know of a fire breathing GS vette replica with a 383 w/9.4:1 CR, hydraulic 230/230 @.050" that sports a Holly 600cfm w/ vacuum 2ndry and dual 4" sidepipes (1-5/8" headers). 3.08 gears= 12.6 seconds at 112mph. The builder stated that a larger carb runs too much vacuum on the secondaries! Whatever…

I've had tremendous success with the Edel 1405 and 1406. Experimenting and keeping records of in-depth testing of each singular change is core! As is only proceeding with tests through the overlapping circuits on an engine that is up to operating temp.

I have often had to come up with a non-conventional rod/jet combo to be happy. The kind of reasoning employed by red65mustang is what'll get you close!

Wonder what eventually did work out for you…
 
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