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70 Challenger 440 bogging and backfiring...

Oystercopy

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Hey guys...so, new Edelbrock 750 carb about a year ago... this is where I think the problems started. I've only owned the car for about 1.5 years, but it seemed to run better with the old Carter, which was replaced due to leaking. New plugs, wires, distributor cap and rotor. Made sure the electronic ignition box was properly grounded to the firewall (that box and the regulator were never grounded properly). She only bogs and does this in first gear, rest are fairly smooth, but low power overall. All cylinders were recently tested for compression and all were good. Only thing I haven't double checked is timing. Also, on advice from a friend, I re-torqued the intake manifold bolts, on a chance they were loose.

Others have said I may have a vacuum leak somewhere, but I don't have any kind of tester for that, nor know how to do it.

Any help appreciated!
OC
 

fasjac

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With the motor idling, You can take some carb or brake cleaner and spray gently around the base of the carburetor, spacer and intake. Any area that you hear a change in idle speed will be a vacuum leak.
don’t spray it on the coil, we don’t need to have a fire. Safety first. 😊
 

Chryco Psycho

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The reality is the Original carbs were tuned for each individual engine which is why there are so many models , the Eddys are 1 size fits all & they are not great carbs at all , tuning the accelerator pump circuit may help the bogging but there is little you can do as Eddy only offers small , stock & 1 size larger squirters to tune with , I have had to drill out squirts in some cases to get enough fuel to prevent bogging . in reality you would be far better off with a Holley style carb like Profrom where you have 12 different pump cams & 14 sizes of squirter to tune with .
 

DaveBob

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If the bogging problem is a hesitation at part throttle that goes away if you floor it, the solution is changing the metering rod springs, and I can help with that. An overall bogging and low power could be resolved with rejetting / remetering. To do this on my car, I installed a wideband O2 sensor, with an air/fuel ratio readout to two decimal places. I put all of the jet / metering rod combinations on a spreadsheet in the order of leanest to richest. Then, as I drove the car and saw the results, I knew what combination to choose next. I shot for an air/fuel ratio of 12.75 to 13.25. Prior to the tuning exercise, I chased a backfire problem that I was certain was fuel system related and it turned out to be a bad coil. But, definitely check your timing first. I run about 10 degrees BTDC initial, which gives me about 35 degrees at WOT and 50 degrees at cruise.
 

Montclaire

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Get a vacuum gauge if you don't have one and make sure you are running the right step-up springs. The rule of thumb is half of whatever the vac is at idle. The eddy carbs are pretty much trouble free once you have them dialed it. Usually the idle/off idle transition is the issue. You might actually be too rich off idle which is what is causing the bog/backfire. Also double check the floats, they are notoriously off from the factory.
 

Oystercopy

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Thanks for all the excellent replies, guys. So, I did go out and readjust the timing, and its definitely better. I don't seem to have the backfiring problem any longer. I still have the bogging in first gear however, so there may be some issues with the carb. Most people I talk to tell me that the Edelbrock are a really GOOD carb, so surprised to hear that maybe they're not. Hmmm.. and I did suspect metering rods/springs, but no way to entertain doing that type of service to the carb. Interestingly, I was always smelling a strong gas smell, so was always suspecting TOO MUCH fuel instead of too little, but that might have been bad timing as well.. it was definitely off. So, if I've got an accelerator pump problem on this carb, how do you even troubleshoot and fix that? I assume the carb has to be disassembled to do any of that, correct? I sure wish I had ANY other type of carb to test on the engine before doing all that, to make sure its the carb. Oh well!
 

Chryco Psycho

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Definately remove the top & check float levels , 7/32 is normal often it will run better @ 3/16 . you need to check this first .
Metering rods can be swapped with removing the top but not the jets meaning any change will be 3-4 steps or more .
The Accel Pump needs to be adjusted as lean as possible without a bog , you should have 3 adjustments in the accell pump arm , moving the rod closer to the pivot increases the amount of fuel delivered & moving it outward decreases . There are only 3 squirters available this controls how fast the fuel is delivered , smaller than stock , stock & larger , often the largest one is not enough so I have drilled them with numbered drills in the past . Start changing settings 1 at a a tie & see which direction is improving the response .
As for Eddy being a good carb well I guess it is better than a fuel leak but anything is better in my experience , I trade them or give them away or toss them in the trash .
 

Montclaire

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I’ve pulled two Holleys in favor of Edelbrocks over the years, I guess it depends what you are more comfortable with. I find the eddys very easy to tune and work on. They are also less prone to leaks. If you can set your timing and change your spark plugs, you can tune an edelbrock.

How do you know you have an accelerator pump problem? There is an adjustment on the arm, the hole furthest from the carb is the smallest pump shot.
 

Montclaire

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Some basic info to get you started. I wouldn’t worry about the jets right off the bat, fully tune what’s in there first and get a baseline. You can literally change springs/rods in 30 seconds, and that’s if you’re slow.
 

Chryco Psycho

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We were on the dyno about 20 months ago we tuned a Proform carb in & the dyno operator claimed we could make the same HP with one of the original Carter AFBs so after we got it dialed in for best power , I went through the Carter & made sure everything was clean & adjusted correctly & we bolted it on . The engine lost 50 HP instantly .
Not all Holleys are great carbs but if you have one of the modern ones with removable air bleeds etc I can typically gain 40 HP over any Carter / Eddy carb , the Crater were better as they were dialed in for each engine but the Eddys are just one size fits all & it doesn't , I have spent weeks modifying & adjusting customer Eddy carbs to never work great , then swapped on a Holley & had it dialed in with better performance in 1-2 hrs .
Adding to this I have taken a couple of brand new Eddy carbs out of the box & found float bowl walls completely missing so the area where the air door counter weight is full of fuel , try to return a carb like this Eddy will not replace it , their QC is terrible & the warranty is worse .
 

moparleo

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Ok the usual...Holley is great and Edelbrock is trash...The world according to Chryco.. Edelbrock seems to be doing ok.
You will find that a lot of people have their personal preferences on different parts and forget that most people are not looking for racing info but just want their car to run without problems.
Don't spray any flammable liquids anywhere on the engine. The purpose of doing this is to find a vacuum leak. Any type of fluid, including water will change the engine rpm if there is a leak. With a flammable the speed will increase, with water it will decrease. Same result, different method. Spray bottle of water is much safer.
Download a service manual . They are free I will post a link.
Round up some basic hand tools f you want to service/ learn to work on your car. We all need them. Plenty of info available online and numerous Youtube videos that you ca watch. Not all info is correct but if you watch enough of them you should be able to "separate the wheat from the chaff."
Service Manuals – MyMopar
Tuning the Edelbrock AVS Carburetor
 
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