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I need help understanding this. Please, Shed some light on it for me.


MadMax_636

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So, I got a replacement carb since mine developed a crack in the bowl. I didn't get a 1.08 Venturi since at the time I thought it was the boosters. I thought the boosters were the Venturi...Yes...

So, after installing the new carb its running super rich and I'm about to put new jets in but can I just put the old boosters into the new carb and it will make it run leaner? That is because the current boosters are pretty larger and the old one is rather small in comparison.

Ive got a really bad off idle bog/hesitation. Ive tuned and tested the accelerator pump and its either doing a to rich or to lean. Ive noticed the tail pipe is wet. Like condensation or Un-burned fuel.

Im still learning about carbs so any info is very much appreciated!!
 


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Uncle Gump

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It's been awhile since I've worked with these... Typically main jets are roughly 4X the venture size. The smaller boosters will allow the main circuit to come ON sooner. So if you were to install the smaller boosters and leave the bigger main jets in... I think your rich problem would get even worse.

I would just swap the mains and the boosters from your old carb into the new one and see where you're at.
 

19Walt93

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The jets and boosters are sized to the throttle bores and venturis. Putting parts from 2 different size carbs together can work but it's going to take some time tweaking to get it right. Just because they bolt in doesn't mean they'll work properly.
 

kimcrwbr1

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Put smaller jets in it .042 as far as the hesitation I found putting a power valve that opens at 8hg helped alot with the dead spot in mine... I you pull the carb always install new carb base gaskets.
 

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I agree with Walt, I would not swap the boosters - it will change too many things at once and make it very difficult to figure out. The air corrector jets are in the boosters so those will change at the same time. I do not recall if the idle jets are removable on those carbs, though I could look at an old carcass when I get home. I think they are tubes in the booster block. Given it is off-idle, the idle jets are what you should look at first. The idle fuel circuit has a separate outlet that is tuneable with the idle needles that is active at true idle - but once the throttle plates move away from those outlets you're on the full idle jet. The main is not active until the air velocity get high enough to run the booster venturi. Therefore if the idle jet is too big, you can tune that down for real idle but once you crack the plates open you're way too rich.

If you have a vacuum gauge it will help you to determine if the power valve is coming on too soon. Also you want to make sure there is vacuum to the power valve - some of these carbs have internal passages and some it is an external nipple to the cap. If it has an external nipple you must make sure that goes to a correct source. If the vacuum is low when you open the throttle it may be the power valve dumping fuel into it.
 

kimcrwbr1

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The 2150 has air bleed jets/holes in the venturi cluster one on each side of the bolt that holds the cluster in. The 2150a feedback carb controls the air bleed with the solenoid on the back of the carb. I supose you could just drill a couple small air bleed holes on top of the emulsion tubes in the cluster? Without proper air bleed it will always run rich it causes the fuel to atomize before it reaches the venturies.
 

MadMax_636

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The 2150 has air bleed jets/holes in the venturi cluster one on each side of the bolt that holds the cluster in. The 2150a feedback carb controls the air bleed with the solenoid on the back of the carb. I supose you could just drill a couple small air bleed holes on top of the emulsion tubes in the cluster? Without proper air bleed it will always run rich it causes the fuel to atomize before it reaches the venturies.
Thats weird, You say if I dont do that it will always run rich?

When I pulled the plugs they looked burned. As if it was running to lean. Ive put bigger jets into the carb and adjusted the choke for the winter and it seems to be running at a better AFR. They are at a nice color. Before the plugs were basically white.
 

8thTon

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If the carb you got was not a feedback carb it will already have air bleed jets. If it was a feedback carb it will never be right without the control system.
 
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MadMax_636

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If the carb you got was not a feedback carb it will already have air bleed jets. If it was a feedback carb it will never be fight without the control system.
Its not a feedback carb.
 

8thTon

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Its not a feedback carb.
Then it must have air beed jets for both the idle and main circuits, those are an essential part of any carb. They may not be removable, they may just be small holes. They could also be corroded shut if it is a used carb.
 

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This seems like a good explanation of how a carb works. I haven't watched the whole thing yet.

 

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If the carb you got was not a feedback carb it will already have air bleed jets. If it was a feedback carb it will never be right without the control system.
I am here to tell you I converted my 2,8 to a duraspark II with a HEI ignition module, but left the feedback carb in place and it runs beautifully. I am getting 17 mpg which I thought would be a little better than that. Probably was with the computer hooked up. But I have no hesitations or any other problems, and it idles very smooth.

I take that back, I do have one minor problem. When it starts cold, I set the choke and it starts right up and idles fast. After it runs for a few minutes, if I touch the throttle it will drop all the way down to the regular idle speed. This is too slow when the engine is not fully warmed up yet, and it will want to chug and quit.

I found out the electronic carb only has one step on the fast idle cam. After that, the idle control motor and the computer controlled the idle speed. Of course I do not have any of that now. I haven't looked at it very close, but I may be able to rob a regular fast idle cam and retro fit it to my electronic carb.

I was eyeballing those china knock off carbs on Amazon. You can't beat the price, but reading this thread I am glad I did not try one. They all say they are for the larger engines, so they probably have the larger venturi's. I think our original 2.8 carbs have the smallest venturi size they made for the 2150?
 

MadMax_636

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Dry rot and old
I was eyeballing those china knock off carbs on Amazon. You can't beat the price, but reading this thread I am glad I did not try one. They all say they are for the larger engines, so they probably have the larger venturi's. I think our original 2.8 carbs have the smallest venturi size they made for the 2150?
The carb is great if you tune it right, I had to tune change my ambient temp choke over as well as raise the jet size. OEM motorcraft Jets work fine.

You can also get a carb with the same venturis off ebay [New]. Its around 150 after shipping.
 

franklin2

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The carb is great if you tune it right, I had to tune change my ambient temp choke over as well as raise the jet size. OEM motorcraft Jets work fine.

You can also get a carb with the same venturis off ebay [New]. Its around 150 after shipping.
You are right, I found this one. Curious they list it for a 351 and 400 engine. It only flows 287cfm.

 


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