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Old 09-06-2011, 02:49 PM   #1
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Holley double pumper on a 304

Is it hard to tune a 4 barrel Holley double pumper on a 1977 AMC 304? My 77 CJ-7 has one on it and I think it is using a lot of gas to run. I also get a lot of backfire in the carb. If it doesn't start right up it blows a lot of smoke out from under the hood. I'm no mechanic but, I don't think that is good.

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Old 09-06-2011, 02:57 PM   #2
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What are you using your Jeep for?
What size is the carb?
For most of the cars//trucks/Jeep out there, a vacuum secondary carb is the way to go. They're better on gas and much easier for the novice to tune. A 304 doesn't need anything more than a 600 Holley vacuum secondary, unless you're running aftermarket heads, radical cam, high compression, etc. You can tune a big carb to work on a small engine, but you'll never get the response and mileage you would if you ran the right sized carb in the first place.

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Old 09-06-2011, 03:01 PM   #3
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whats the part number of the carb? It should be located on the front side of the choke horn.
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Old 09-06-2011, 04:44 PM   #4
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I use the Jeep for around the town driving and weekend trips to the hills and playing down at the river. I'm not looking for a gas efficient vehicle. I want to have fun on the weekends.

I will try to find the number on the carb and post it.
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Old 09-06-2011, 04:48 PM   #5
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cool, then we can figure it out
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Old 10-03-2011, 06:27 PM   #6
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Okay, so, I have taken a while and here is the info that I think I got off of my carb. I think it is a 6520. Does that sound right? It was kind of hard to find. Does this seem like a big carb for my AMC 304?

Thank you for your help.
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Old 10-03-2011, 06:29 PM   #7
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After doing research this is what I came up with:

6520 600 (F)62,(R)plate 134-39 8.5 4160

What ever that means, lol.
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Old 10-04-2011, 12:46 PM   #8
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It's been a while, but IIRC that means it is part# 6520, 600 CFM, front jets are 62's, the rear plate is a 134, the pump squirters are .039", it has an 8.5 power valve and it's a model 4160.

As I said, it's been a long time, but I don't remember there being a model 4160 double pumper. It is possible that it has been converted, but the expense involved would make just buying a 4150 to start with a better option. Any pics?
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Old 10-04-2011, 01:40 PM   #9
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Easy way to tell if it's a double pumper: When you manually open the throttle blades, does one set open, or do both open? Vacuum secondary carbs are ideal for pretty much all street applications. They're more efficient on street engines, but typically make a little less power. They're a lot more forgiving and easier to tune, as well.
As Oilwell stated, converting a VS carb to a DP is pretty much pointless. You have to replace so much of the carb, it's just more cost effective to buy a new DP. Back in the day, guys would put a screw in the throttle linkage to force the secondaries open mechanically, but this isn't the same thing as a true DP, as you are still lacking the secondary accelerator pump, among several other things.

If the 6520 is the model number, what you have there is an OE installed Holley/Weber, that came on the old Mopar 2.2 and assorted 4 cylinder import engines. It's a "Staged" 2 barrel electronic feedback carb, with a maximum cfm of only 270cfm. That basically means it used a small computer and sensors to control the carb. That means, if you lack the computer and sensors, it's never going to operate correctly. Does it look something like this?

If so, it's garbage. Lose it. It will never flow the cfm your engine needs, it will never provide the fuel your engine needs, and without the computer and an 02 sensor/vacuum solenoid, it will never operate correctly anyway and you're not going to find many people who can actually tune it.

My advice: Get yourself a nice, new Holley 4 barrel with vacuum secondaries. I recommend the 570 Street Avenger. Then get a book on how to tune a vacuum secondary carb, and read it.
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Old 10-04-2011, 02:09 PM   #10
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For just tooling around I'm a fan of Edelbrock carbs. Put it on, do the initial setup, and forget about it. They aren't as tunable as a Holley, but don't need to be. I don't think I've ever installed a carb that was more ready to go out of the box than an Edelbrock.
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Old 10-04-2011, 02:14 PM   #11
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Quote:
Originally Posted by oilwell1415 View Post
For just tooling around I'm a fan of Edelbrock carbs. Put it on, do the initial setup, and forget about it. They aren't as tunable as a Holley, but don't need to be. I don't think I've ever installed a carb that was more ready to go out of the box than an Edelbrock.
I'd agree with that. Edelbrocks are great on stock or mild motors. I'm a Holley man, myself. Never had much luck with Eddys on performance motors.
That said, the Street Avenger is a true bolt on and go Holley. You can't go wrong with either, and it will be a damn sight better than the contraption that's on it now.
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Old 10-04-2011, 02:14 PM   #12
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^^true but they have no place in anything more than a stock motor.
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Old 10-04-2011, 02:29 PM   #13
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I prefer Holleys as well, but for a stock daily driver they can be a pain.

I've had a few Edelbrocks on modded engines and they still do well. The problem is getting them there. That's where the Holley really shines. You can do to a Holley in 30 minutes what would take you all day to accomplish with an Edelbrock and the components on the Edelbrock cost an arm and a leg. Once you get it tuned the Edelbrock will still be happy forever while a Holley will often want some adjustments when the seasons change.

Either carb will work great. I don't remember using a Truck Avenger before, but I may have. If you can bolt it on and forget about it that's great.

Does Holley still make the 4010/4011 series? Those were pretty good carbs. The consistency of the Edelbrock, but could use all the standard Holley tuning parts.
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Old 10-04-2011, 02:36 PM   #14
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Quote:
Originally Posted by oilwell1415 View Post
I prefer Holleys as well, but for a stock daily driver they can be a pain.

Try the Street/Truck Avenger, they really are a snap.

I've had a few Edelbrocks on modded engines and they still do well. The problem is getting them there. That's where the Holley really shines. You can do to a Holley in 30 minutes what would take you all day to accomplish with an Edelbrock and the components on the Edelbrock cost an arm and a leg. Once you get it tuned the Edelbrock will still be happy forever while a Holley will often want some adjustments when the seasons change.

Agreed, lol.

Either carb will work great. I don't remember using a Truck Avenger before, but I may have. If you can bolt it on and forget about it that's great.

You really can, but they still retain all the tunability of the traditional Holley 4 barrel.

Does Holley still make the 4010/4011 series? Those were pretty good carbs. The consistency of the Edelbrock, but could use all the standard Holley tuning parts.

I believe so, but they are pretty expensive. Around $650 last I saw. Street Avenger in 570 or 670 is under $400.
Still can't figure out the multi-quote.
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Old 10-04-2011, 02:49 PM   #15
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Quote:
Originally Posted by Mr. Sinister View Post
Still can't figure out the multi-quote.
You don't need multi quote for what you are doing. You just have to break up the post you want to insert comments in as shown below. Substitute [...] every where you see {...} and it will separate them into separate quotes and you can write between them.

{QUOTE=oilwell1415;1627215}I prefer Holleys as well, but for a stock daily driver they can be a pain.{/quote}

{quote}I've had a few Edelbrocks on modded engines and they still do well. The problem is getting them there. That's where the Holley really shines. You can do to a Holley in 30 minutes what would take you all day to accomplish with an Edelbrock and the components on the Edelbrock cost an arm and a leg. Once you get it tuned the Edelbrock will still be happy forever while a Holley will often want some adjustments when the seasons change.{/quote}

{quote}Either carb will work great. I don't remember using a Truck Avenger before, but I may have. If you can bolt it on and forget about it that's great.{/quote}

{quote}Does Holley still make the 4010/4011 series? Those were pretty good carbs. The consistency of the Edelbrock, but could use all the standard Holley tuning parts.{/QUOTE}
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Old 10-04-2011, 03:26 PM   #16
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before you go changing the carb settings, do a tune up. Replace spark plugs, cap/rotor and maybe wires if they are old.

Did it ever run right? If so, its your consumables not your adjustments causing the rough running and hard starts with backfires.

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