I purchased an edelbrock book called how to re-build and modify carter/edelbrock carburetors by dave emanuel and it is saying i can quicken the opening rate of the afb secondary air valve by removing material from the counter weight. How do i do this? i took the secondary air valve out of the carburetor i am just wondering where to shave the weight off at? and if somone can show me how to do it by sharing photo's or pictures or anything?
edelbrock carburetor modifications
- Thread starter pjc360
- Start date
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Place the weight back in the base and play with it. Notice where the weighted side is?
OK, you can die grinder it off or drill holes. But I often ask myself, what MONSTER motor would need this mod?
Better be one hot *** engine to do this. And I really mean it better be one smoking *** kicking mutha of a engine.
Ya also might wanna add a second pump shot to the back side of the carb since these carbs tend to go lean under a whopping stomp of the go pedal.
OK, you can die grinder it off or drill holes. But I often ask myself, what MONSTER motor would need this mod?
Better be one hot *** engine to do this. And I really mean it better be one smoking *** kicking mutha of a engine.
Ya also might wanna add a second pump shot to the back side of the carb since these carbs tend to go lean under a whopping stomp of the go pedal.
I guess its not that hot of an engine but its defanatly not a whimpy engine ether, its running at 320 horse power and 425 ft lbs of torque. The main complaint i have with this edelbrock carb is the off idle stumbling. Should i take the accelerator nozzles off and drill them out a tad bigger? i have the accelerator pump set on the richest side and its still there a little bit. I have no complaints with the four barrell side of it or mid throttle, its just that off idle stumble thats driving me nuts. and i know the timing is perfect.
timing is at 5 degrees initial and i set the throttle steady at around 2500 to 3000 rpm and set it at 35 degrees that way and it seems to be running just right that way, it starts up at the first turn of the key.
67Dart273
Well-Known Member
If you have an engine that runs at 5BTC it's not nearly wild enough to screw around with the secondary weights
Likewise, I doubt you need to drill out the pump
Does the pump "cut in" instantly when you move the throttle? (Look down the throats/ engine off)
Have you consulted "the book" (download at Edelbrock) and properly adjusted the accellerator pump? Which hole is the link in? Float level? Engine temp? Trouble with vapor lock?
Likewise, I doubt you need to drill out the pump
Does the pump "cut in" instantly when you move the throttle? (Look down the throats/ engine off)
Have you consulted "the book" (download at Edelbrock) and properly adjusted the accellerator pump? Which hole is the link in? Float level? Engine temp? Trouble with vapor lock?
Salty Dog
Well-Known Member
Edelbrock offers pump clusters, 3 in a pack, 1 smaller, 2 larger. The pump arm should be at the hole closest to the carb body. IMO, you could use more intial. Only 5 degrees initial?
Stock cammed 340 with headers?
Stock cammed 340 with headers?
C130 Chief
Mechanical Genius
If you have an off idle stumble, making the secondaries air baffle open faster won't fix it. Doing so might however introduce a mid throttle stumble. Going out on a limb here, I'm guessing you want the carb to be more smooth, not less. An off idle stumble is generally one of three things: a vacuum leak, improper pump shot, or delayed main circuit enrichment. This assumes the float levels are set right. AFB type carbs are really sensitive to this, and Edelbrock carbs are known for being off out of the box.
Can you "step through" the stumble? That is, if it stumbles with slight throttle movement, but roars back to life if you press the pedal more, suspect a vacuum leak on the timed vacuum side, such as the advance unit. Disconnect the vacuum advance and cap the port on the carb, see if that helps. If you can "feather" the throttle, or open it real easy (drive like a grandma) and it does not stumble, but a quick poke of the pedal causes a 0.5-1.0 second bog, but then it runs fine, it might be pump shot. If it's a little doggy for the first 1/4 throttle and then responds with more throttle opening, you may need stiffer springs under the metering rods (and in fact you probably would benefit from stiffer springs, but make sure you don't have a bigger problem first).
BUT, before you get too carried away with the carb, you should address the basic tune up. Specifically the base timing. 5 degrees BTDC at idle is not enough if you are running any sort of performance cam. In fact, with the factory cam, a 340 really liked 10 or more, but the factory set it really conservative for smooth idle, easy starting and emissions reasons. You'll probably be happier with 12 degrees initial and 36 total, as most small blocks are. With 35 total now and 5 initial, basic math would give you 42 total at 12 initial. Probably too much, but 30 degrees at the crank, (15 distributor) is typical of OEM smog era distributors. Mopar electronic ignition was a good system, but the factory advance curves were anything but high performance.
Assuming your vacuum advance works, and does not leak, you could try connecting it to full manifold vacuum (drivers side port). This will give you more advance at idle, possibly a lot more. In a situation like yours it may help low RPM response, but you are masking the real problem, not solving it.
Can you "step through" the stumble? That is, if it stumbles with slight throttle movement, but roars back to life if you press the pedal more, suspect a vacuum leak on the timed vacuum side, such as the advance unit. Disconnect the vacuum advance and cap the port on the carb, see if that helps. If you can "feather" the throttle, or open it real easy (drive like a grandma) and it does not stumble, but a quick poke of the pedal causes a 0.5-1.0 second bog, but then it runs fine, it might be pump shot. If it's a little doggy for the first 1/4 throttle and then responds with more throttle opening, you may need stiffer springs under the metering rods (and in fact you probably would benefit from stiffer springs, but make sure you don't have a bigger problem first).
BUT, before you get too carried away with the carb, you should address the basic tune up. Specifically the base timing. 5 degrees BTDC at idle is not enough if you are running any sort of performance cam. In fact, with the factory cam, a 340 really liked 10 or more, but the factory set it really conservative for smooth idle, easy starting and emissions reasons. You'll probably be happier with 12 degrees initial and 36 total, as most small blocks are. With 35 total now and 5 initial, basic math would give you 42 total at 12 initial. Probably too much, but 30 degrees at the crank, (15 distributor) is typical of OEM smog era distributors. Mopar electronic ignition was a good system, but the factory advance curves were anything but high performance.
Assuming your vacuum advance works, and does not leak, you could try connecting it to full manifold vacuum (drivers side port). This will give you more advance at idle, possibly a lot more. In a situation like yours it may help low RPM response, but you are masking the real problem, not solving it.
C130 Chief
Mechanical Genius
To reduce the mass of the counter weight, you would remove material beginning at the farthest point from the pivot shaft. Previous editions of Emanuel's book showed a really good picture of this.
67Dart273
Well-Known Member
C130, in addition to what you said, he may have a large enough cam and not enough timing, that he's got the idle screw cranked way up and the throttle blades ARE OUT OF THE TRANSFER SLOTS.
Crank up the timing, screw down the idle, and readjust the mixture.
Crank up the timing, screw down the idle, and readjust the mixture.
my vaccume advanced hose is connected to full manifold vaccume. And i set the timing at 5 degrees initial because thats what it honestly sounds the best at, and its not a 340 its a 360 magnum, i have had it dynoed and it is putting out 319 hp and 424 ft lbs of torque. the initial timing was set at 12 degrees but it was popping out the exhaust and not running right at 12 degrees, engine tempature never gets above 195 but normally runs at 190. The accelerator pump link is sitting in the very top hole so its set at richest.
I guess i could try bumping the timing up to 8 or 10 degrees initial but it really sounds good at 5 initial. it starts up at the first turn of the key when sitting at 5 degrees initial.
I searched all over the web trying to find out what my engine needed to be timed at and couldnt find any specs because its a mopar crate engine. I talked to my mechanic buddy whop is running a 400hp ford 428 big block and he told me his engine runs perfect at 5 degrees initial timing as well, and when it was running poorly he was the one who suggested bumping it down a little bit.
I guess i could try bumping the timing up to 8 or 10 degrees initial but it really sounds good at 5 initial. it starts up at the first turn of the key when sitting at 5 degrees initial.
I searched all over the web trying to find out what my engine needed to be timed at and couldnt find any specs because its a mopar crate engine. I talked to my mechanic buddy whop is running a 400hp ford 428 big block and he told me his engine runs perfect at 5 degrees initial timing as well, and when it was running poorly he was the one who suggested bumping it down a little bit.
How do i make sure the throttle blades are not out of the transfer slots 67dart273? i will bump the timing up to 8 degrees initial and go from there with the idle turned up. I didnt think 5 degrees initial would not be enough for a 360 since my buddys 428 ford runs at that just perfectly as well? and c130 chief hit it right on the head, the stumble is the type to where i can feather the throttle but if i go to stomp on it, it will bog and spit and sputter for a second or so then it will catch up and go. So what do you guys suggest i set the timing at? should i set the initial at 10 or 12? then i cant remember if its called setting the vaccume advanced or mechanical timing when you set the throttle steady at 2500 rpm and dial it in? So i need to know what i should set it at while at an idle and what to set it at while at a steady 2500rpm?
67Dart273
Well-Known Member
Somebody else's engine timing has nothing to do with you. Timing and advance curve depends on the load on the engine, as in a heavy truck versus a light car, compression ratio, the design of the combustion chamber, the camshaft specs, and the quality of fuel available, and probably a few other things.
FIRST generally running at full manifold vacuum is not what you want. What I would do is unhook the vacuum and LEAVE it unhooked until you get it dialed in a little more, and THEN try ported vacuum
LEARN how, and we can help you to figure out your timing
If there is ANY question as to the timing marks accuracy, buy or build a piston stop and check the marks. Easy to do
Degree the wheel, buy the proper timing tape, or buy a "dial back" timing light so you can see what the timing is advancing to, and how fast.
START by setting the timing to about 35* TOTAL, that is, vacuum disconnected AND LEAVE it disconnected, at a fairly high RPM, and then wind up the engine to make sure it does not advance further at higher RPM
Even if you have not degreed the wheel, you can MEASURE for 35* and put a temporary referance. Just measure around the balancer CAREFULLY with a thin flexible tape to get the circumference. Then figure how many inches per degrees, then figure out how many inches makes 35* (to start) and make your mark.
Checking the marks with a stop and adding a 35* reference should not take an hour. I found it easiest to mark a wheel when lying under the car, looking up. Less junk in the way.
NOW when you get your 35* "power time" set, idle it down as slow as it'll go, and see where the initial landed. This will tell you if the distributor curve is useful or AFU.
With much of a cam at all, you want AT LEAST 10-12, and possibly more like 15 initial, with around 32-40 total mechanical, depending on engine conditions.
As I said before, running too little initial with even a mild cam causes you to have to screw in the idle screws more, and this can open the throttle up until the idle transition slots are exposed. YOU CAN SEE THIS by looking down the throats with a flashlight. AND THIS WILL cause off -idle stumble.
Don't discount there could be dirt in the various bleed passages of the carb. It might pay to pull the carb apart, get a "snorkel" on a carb cleaner spray can and pressurize all the tiny passages in the carb. WATCH your eyes.
FIRST generally running at full manifold vacuum is not what you want. What I would do is unhook the vacuum and LEAVE it unhooked until you get it dialed in a little more, and THEN try ported vacuum
LEARN how, and we can help you to figure out your timing
If there is ANY question as to the timing marks accuracy, buy or build a piston stop and check the marks. Easy to do
Degree the wheel, buy the proper timing tape, or buy a "dial back" timing light so you can see what the timing is advancing to, and how fast.
START by setting the timing to about 35* TOTAL, that is, vacuum disconnected AND LEAVE it disconnected, at a fairly high RPM, and then wind up the engine to make sure it does not advance further at higher RPM
Even if you have not degreed the wheel, you can MEASURE for 35* and put a temporary referance. Just measure around the balancer CAREFULLY with a thin flexible tape to get the circumference. Then figure how many inches per degrees, then figure out how many inches makes 35* (to start) and make your mark.
Checking the marks with a stop and adding a 35* reference should not take an hour. I found it easiest to mark a wheel when lying under the car, looking up. Less junk in the way.
NOW when you get your 35* "power time" set, idle it down as slow as it'll go, and see where the initial landed. This will tell you if the distributor curve is useful or AFU.
With much of a cam at all, you want AT LEAST 10-12, and possibly more like 15 initial, with around 32-40 total mechanical, depending on engine conditions.
As I said before, running too little initial with even a mild cam causes you to have to screw in the idle screws more, and this can open the throttle up until the idle transition slots are exposed. YOU CAN SEE THIS by looking down the throats with a flashlight. AND THIS WILL cause off -idle stumble.
Don't discount there could be dirt in the various bleed passages of the carb. It might pay to pull the carb apart, get a "snorkel" on a carb cleaner spray can and pressurize all the tiny passages in the carb. WATCH your eyes.
I just cleaned the entire carburetor, its brand new as well less then 3000 miles. And i dont think i have to mess with timing tape because there is already a mark on the balancer that lights up with the timing light. So i set mechanical first? rev it up to a steady 2500 rpm and set it at 35 degrees then let it down to an idle and chaeck what the initial is? i can do that right now and let you guys know.
Also when i timed it the first time i had the vaccume advance hose plugged off. and i think the advanced vaccume house is hooked up to full manifold vaccume because the vaccume advance house is plugged into the drivers side port of the carburetor. So with it being plugged into the drivers side port i should be running a little more then 5 degrees initial correct? and this engine's specs are all over the web its the 300hp 375 ft lbs of torque 360 magnum crate engine. I have heard the cam in it is relatively stock or (mild) i got it dynoed last week just curious as to what it was putting out with what i have on it and it is not cranking out alot more horsepower then listed by mopar but the torque is up at 424 and it is rated at 375 by mopar. I dont understand why mopar under rate's there crate engines.
So i just pulled the vaccume advance house off and i was wrong it was not on the full manifold vaccume side of the carburetor it was on the left side and the drivers side port is plugged off. So i plugged the vaccume advance hose set the initial timing at 10 degrees then i had my girl friend get in it and hold the gas pedal at a steady 2500rpm and i set my timing light at 35 degrees and it was running more at like 38 to 40 degrees with the light dialed in at 35 so i pulled the distributer back just a tad got out and checked it again with the light dialed in at 35 and it was dead on. Told the old lady to let go of the gas and get out then i hooked the vaccume advance hose back into the passenger side port of the carburetor and i attempted to adjust the idle but i noticed something. The nut that is holding my gas pedal cable to the carburetor is pretty big and when i turn the idle screw in it pushes against that nut and there fore its pusing the gas pedal down.... so i backed it off untill it wasnt pushing the gas pedal down and it was idleing pretty darn close to right, maybe just a hair high but sounded good. I reved it up a few times and no popping thru the exhaust or anything and sounded pretty good. With the initial set at 10 degrees instead of 5 it seems to rev up faster, with faster response. and it idled a little bit higher then it did while sitting at 5.
Another thing i noticed that i think is worth mentioning, you can not advance my distributer any further then 12 degrees initial. i advanced it all the way to where it would not move anymore and checked it while at an idle and it was at 12 degrees. My old man installed the distributer on this engine and he was the smartest mopar man i have ever met, unfortunetly he passed away a year and a half ago, is it possible he installed this way to where you could not advance it any further then 12 degrees? i'm thinking he put the distributer in that way so it could never be advanced any further then 12 degrees initial so that the engine could not be hurt. But anyways its running at 10 degrees initial and 35 degrees at 2500 rpm. with the vaccume advanced hose being plugged off while timing it. I hope this sounds better then 5 degrees initial. the engine reved up a little quicker at 10 degrees initial vs 5 degrees i did notice that much.
Another thing i noticed that i think is worth mentioning, you can not advance my distributer any further then 12 degrees initial. i advanced it all the way to where it would not move anymore and checked it while at an idle and it was at 12 degrees. My old man installed the distributer on this engine and he was the smartest mopar man i have ever met, unfortunetly he passed away a year and a half ago, is it possible he installed this way to where you could not advance it any further then 12 degrees? i'm thinking he put the distributer in that way so it could never be advanced any further then 12 degrees initial so that the engine could not be hurt. But anyways its running at 10 degrees initial and 35 degrees at 2500 rpm. with the vaccume advanced hose being plugged off while timing it. I hope this sounds better then 5 degrees initial. the engine reved up a little quicker at 10 degrees initial vs 5 degrees i did notice that much.
67Dart273
Well-Known Member
When you set your total, YOU MUST "guess it in" as you did, but WIND THE ENGINE UP MUCH more than 2500. What you want to confirm is whether you have a "long slow" distributor curve, which may advance MORE past the 2500 figure
It's hard to tell from your description---you DO have a "dial back" timing light, is that right?
A "cheat" way of getting the timing past 10-12 is to run the plug wires around one hole and retime it. There is NO REASON to have the vacuum can hit something at 12*, and you may very well find you want more than that, depending on the TOTAL (without vacuum)
LEAVE THE FREEKIN VACCUUM OFF until you get this sorted out, UNDERSTAND?
I don't know how to make that any more clear. Leaving it off will be one less thing to "fight with."
You can EASILY tell which one is ported and which one is vacuum. --- READ the book. If you don't have one, wander over to Edelbrock and download one
http://www.edelbrock.com/automotive_new/mc/carbs_acc/pdf/carb_owners_manual.pdf
Ported is Passenger side Full vacuum is driver side
It's hard to tell from your description---you DO have a "dial back" timing light, is that right?
A "cheat" way of getting the timing past 10-12 is to run the plug wires around one hole and retime it. There is NO REASON to have the vacuum can hit something at 12*, and you may very well find you want more than that, depending on the TOTAL (without vacuum)
LEAVE THE FREEKIN VACCUUM OFF until you get this sorted out, UNDERSTAND?
I don't know how to make that any more clear. Leaving it off will be one less thing to "fight with."
You can EASILY tell which one is ported and which one is vacuum. --- READ the book. If you don't have one, wander over to Edelbrock and download one
http://www.edelbrock.com/automotive_new/mc/carbs_acc/pdf/carb_owners_manual.pdf
Ported is Passenger side Full vacuum is driver side
..........If u had ur base timing at 5* and 35*total revved up , then u set ur base to 10* and revved it up u would have 40* total, because u added 5* more to the equasion..............u can adjust ur vacuum can some to limit the total timing........i would forget about ur vacuum advance for now, just plug it......rev it up to 3000 and time it to 35*.......idle down, check base timing, prolly around 20*......if it starts fine, leave it for now, go for test drive...........ur done.......yeah haw......kim.....
What i did was i un plugged the vaccume advance hose and plugged it off, then i set the initial timing from 5 degrees to 10 degrees, then i applied a steady throttle at 2500 to 3000 rpm and dialed it in at 35 degrees. then i plugged the vaccume advance house back in and that was that. It started a bit easier sitting at 5 degrees initial timing, but i noticed it runs better down the road with it set at 10 degrees as opposed to 5 degrees.
Does this sound about right? i did not mess with the vaccume advance at all, i just plugged the hose off while timing it then plugged the house back in after i was done. It seems to run better down the road at 10 degrees but it was starting a little easier at 5 degrees.
Does this sound about right? i did not mess with the vaccume advance at all, i just plugged the hose off while timing it then plugged the house back in after i was done. It seems to run better down the road at 10 degrees but it was starting a little easier at 5 degrees.
Why does my engine start better at 5 degrees initial rather then 10 degrees? but it runs down the road better with crisper response when set at 10 degrees initial. Is Having it set at 35 degrees while at 2500 to 3000 rpm good? I have heard some people say to get more like 40 to 45 degrees at 2500 to 3000. It seems to be running pretty good right now. The main thing i gotta do now is figure out wich metering rod is 1 step richer from the 7047 edelbrock metering rod. I tried running a 7347 metering od and it was surging in and out pretty bad, threw the 7047's back in and its no longer surging but i can tell it wouldnt hurt to try the next richer rod up, i am running the silver step up springs as well and a 1 inch phenolic 4 carburetor spacer.
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