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Old 01-04-2015, 08:58 PM   #1
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Carb flaps not opening?

I came to this part of the forum because you guys know the most about carburetors. I recently put a new engine and an edelbrock carb on my 1999 mustang GT, and it ran really really sweet the first day. It is however, a used carb. And Im not sure what flaps are supposed to open and in what conditions, but I don't think its happening correctly. I am used to dirt bike carburetors so I understand the concept of metering rods, main jets, and how the circuits relate, I just don't know about all of the flaps. Things have changed with the carb and now it only runs with the choke on

Looking at the carb as it sits on the car, the main choke flap opens as its supposed to, and the butterfly valve for the throttle in the 2 barrels under said choke flap also work correctly. That is what im calling the front of the carb.

The 2 barrels closest to the dash/rear do not open at all. The flap on top doesn't follow the other choke flap's movement like I assume its supposed to, and the butterfly valves on the bottom do not open at all. I can wiggle the top flaps completely open and closed with my fingers and they go really easily, but the ones on the bottom don't move easily and I don't want to reef on them. They worked when I put the carb on the car...
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Old 01-04-2015, 09:58 PM   #2
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I'm assuming you have vacuum secondaries and not mechanical.
If that's the case then you may a clog or vacuum issue.
If they are mechanical, then something may have disconnected or be gunked up.
How clean was it before installing?



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Old 01-04-2015, 10:39 PM   #3
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Not at all a carb expert, but here is what I learned from my carter (the predecessor to your 4 barrel EB). The top flaps at the front which move easily are for your choke. Either electrical or manual (I'm assuming not old-school thermostatic), the choke moves these to cut off air for starting. The butterflies directly below this are your primaries - used at lower RPMs. The rear butterflies are your secondaries, and those open up when you get on it under load. So both sets of butterflies actually shouldn't open the same.

You mentioned the choke plate was freely moving - is this all the time? If you have an electric choke, it should only move when gas is applied (then it is moved however far the spring in the choke has twisted due to heat). When you're not touching the gas, there is a part of the throttle linkage which keeps it held at the same angle as the car warms up. Once warm, it stays in the vertical position until the engine cools again, and will stay open until you touch the gas again at the next start up (or whenever). Not sure if manual choke behaves quite the same, mine is electric.

I'm not the best at diagnosing carbs, but hopefully this helps a little bit - or at least tells you what isn't wrong!
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Old 01-04-2015, 10:39 PM   #4
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Quote:
Originally Posted by Aggiesrok View Post
I'm assuming you have vacuum secondaries and not mechanical.
If that's the case then you may a clog or vacuum issue.
If they are mechanical, then something may have disconnected or be gunked up.
How clean was it before installing?



Chevy runs deep, don't step in Chevy.
Oh okay thank you. I bet they are vacuum secondaries. I just googled that and it seems that most Edelbrock carbs use those
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Old 01-05-2015, 09:34 AM   #5
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Quote:
Originally Posted by ER12883 View Post
Not at all a carb expert, but here is what I learned from my carter (the predecessor to your 4 barrel EB). The top flaps at the front which move easily are for your choke. Either electrical or manual (I'm assuming not old-school thermostatic), the choke moves these to cut off air for starting. The butterflies directly below this are your primaries - used at lower RPMs. The rear butterflies are your secondaries, and those open up when you get on it under load. So both sets of butterflies actually shouldn't open the same.

You mentioned the choke plate was freely moving - is this all the time? If you have an electric choke, it should only move when gas is applied (then it is moved however far the spring in the choke has twisted due to heat). When you're not touching the gas, there is a part of the throttle linkage which keeps it held at the same angle as the car warms up. Once warm, it stays in the vertical position until the engine cools again, and will stay open until you touch the gas again at the next start up (or whenever). Not sure if manual choke behaves quite the same, mine is electric.

I'm not the best at diagnosing carbs, but hopefully this helps a little bit - or at least tells you what isn't wrong!
Yeah the main choke flaps does exactly what you just said. I just pulled the carb off last night to fatten up my main jets and got confused by the secondary choke flap that seems totally disconnected (because its vacuum operated). Then the secondary throttle valves on the rear of the carb didn't seem like they were opening, but that is because the choke was closed. Apparently, when the choke is closed, there is a lever that blocks the rear 2 barrels from flapping open. So if I open the choke manually and then give it gas, she is capable of WOT just fine.
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Old 01-05-2015, 07:05 PM   #6
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Sounds like you're on your way. Cool.


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Old 01-07-2015, 12:45 PM   #7
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Sounds like you're on your way. Cool.


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Yeah thank you guys for the help. My next issue that I am having is that when the car is warm, the thing gets a bad off idle stumble. It happens out of stop lights a lot. I am suspicious of my metering rod springs in conjunction with my fuel pump.

The carb was off of a monte carlo with a 5.7L engine. Im guessing that creates a more powerful vacuum at part throttle, which would require stiffer metering rod springs than my 4.6L needs.
On top of that, I fattened up 2 of my main jets for the cold weather. Originally the diameter was .090". I drilled them out to .107", which is a 19% increase in fuel delivery :/ Its -5 degrees here though and the carb supposedly was jetted for 80 degree weather originally.

Another possibility is the fuel pump delivering too much fuel. It is MR. Gasket 42S I believe. Either way, its the one they say you can run a 4, 6, or 8 cylinder engine off of. It flows 35GPH and the package says it runs 4-7 PSI. I don't know what that 4-7psi deal means. Does that mean I can put an inline FPR on it that allows 4-7 psi without hurting the pump? Or does that mean that the pump will self regulate at 4-7 psi?
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Old 01-07-2015, 01:08 PM   #8
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Sounds like a basic street pump, no need to use a regulator. The carbs can only handle up to 7 psi, which is why you need a regulator when using a High pressure or high volume fuel pump. Ideally for a stock or mildly modified engine, you will see 5 psi at idle and depending on Carb flow, and fuel delivery from the pump, a maximum of 7 psi. When you get into extensive mods, you will then need a high volume fuel pump with a regulator. On a vacuum secondary carb, would be difficult for you to see secondary opening, if looking at it under the hood, because in neutral, you would not build enough vacuum to see the secondaries operate, unless you lightened the springs, that operate the secondaries.
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Old 01-07-2015, 01:28 PM   #9
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My secondaries feel like they just flap open and close with no resistance when I wiggle them with my finger. They are attached to what looks like it is a counter weight? When should these be opening? I reved it up a little and I didn't see them open much if at all :/
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Old 01-07-2015, 01:28 PM   #10
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Have you checked to make sure that the accelerator pump is functioning correctly?
It may not be adjusted properly for the smaller displacement engine.
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Old 01-07-2015, 01:36 PM   #11
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Have you checked to make sure that the accelerator pump is functioning correctly?
It may not be adjusted properly for the smaller displacement engine.
That's a really good thought actually. I had a problem with that at first. There are 3 different holes you can plug the accelerator pump linkage into that makes it respond to throttle movement, and it was originally plugged into the top one, which flooded the car out pretty bad at first. Then I moved it to the middle one which seems better, but the bottom hole seems like it will be stuck open a little at all times when I plugged it into that one. :/ Its my cheapest option right now I suppose. I have exactly $3 in my bank account until my paycheck and my student loans come in so im gonna try that idea.

I just have to get the right sized serpentine belt first
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Old 01-07-2015, 01:43 PM   #12
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That's the nice thing about an Edelbrock, they are very easy to adjust and experiment with. I highly recommend purchasing a tuning kit for it. They come with a large selection of springs, metering rods, jets, etc.
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Old 01-07-2015, 02:55 PM   #13
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My secondaries feel like they just flap open and close with no resistance when I wiggle them with my finger. They are attached to what looks like it is a counter weight? When should these be opening? I reved it up a little and I didn't see them open much if at all :/
On a Vacuum secondary, engine vacuum dictates opening of the secondaries, not sure how your carburetor works, which is why I always preferred Holleys, on the Holly, there is a diaphragm, with a springs which is color coded, to dictate the weight of the spring, which allows you to alter the opening of the secondaries based on the spring weight. The lighter the spring the quicker the secondaries open. Back in the day, when you floored a 4 barrel especially on a quadrajet, you would get a flat spot when it transitioned from primaries to all 4. If you had a holley I would probably be able to get you close just through the forum alone.
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Old 01-07-2015, 02:56 PM   #14
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I think I am going to get one of those as soon as I can.
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Old 01-07-2015, 02:57 PM   #15
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That's the nice thing about an Edelbrock, they are very easy to adjust and experiment with. I highly recommend purchasing a tuning kit for it. They come with a large selection of springs, metering rods, jets, etc.
My experience is with Holleys, not trying to contradict you, but for me the Holley is so versatile, I prefer it's tuneability.
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Old 01-07-2015, 03:14 PM   #16
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Originally Posted by DeepImpactPony View Post
On a Vacuum secondary, engine vacuum dictates opening of the secondaries, not sure how your carburetor works, which is why I always preferred Holleys, on the Holly, there is a diaphragm, with a springs which is color coded, to dictate the weight of the spring, which allows you to alter the opening of the secondaries based on the spring weight. The lighter the spring the quicker the secondaries open. Back in the day, when you floored a 4 barrel especially on a quadrajet, you would get a flat spot when it transitioned from primaries to all 4. If you had a holley I would probably be able to get you close just through the forum alone.

Yeah I hear the Holley is a better performance oriented carb and the edelbrock is just more oriented as a dd carb for a mild street car than the holley is. I have a brand new Holley sitting on the shelf at work I could probably get cheap as chips. Too bad I don't have any chips lol.


I decided to go with edelbrock because I had to buy a used carb, and it seemed like they would be a safer bet as far as holding up for decades in a carboard box in some guy's garage
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Old 01-07-2015, 03:31 PM   #17
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Another thought I had:


I still have my electronic ignition as well as my ECU and O2 sensors.


Could I get an OBDII to USB plug in and use the Torque app on my phone to watch my AFR change at different throttle positions/RPMs? I know the stock O2 sensors aren't wide band, but as long as I can get the AFR between 10:1 and 17:1 shouldn't they read?


I cant afford a wideband O2 sensor kit right now, that's why Im considering this idea
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Old 01-07-2015, 04:08 PM   #18
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Old 01-07-2015, 06:56 PM   #19
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yeah ive been watching those videos like they're my bible lol. Thans tho
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