73 Carb issues $V

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73CobraJet

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Hi all, I'm having issues with my 73 CJ carb. The car seems to start and run fine but when driving once in a while it seems to cut out a bit. The second issue is when I just run the car in the garage it will run for a bit the the idle seems to just drop off and eventually just die. Not sure what to look at as I have Holley carbs or the Autolite carbs all these years. i really do NOT want to take it apart!! Any help would be appreciated. Thanks. Also thinking about going Fuel Injection or Holley spread bore. Any thought on the least intrusive FI system. Dont want a whole lot of return lines, lots of computer stuff in the car. Don't want to drill holes in a Q code!!
 
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I would make sure it's nothing else, like the ignition, before tearing into the carburetor. Make sure the points are gapped correctly, better to set them by dwell. A loose or bad condenser can cause your symptoms, as can a bad coil or one that isn't well grounded. Make sure the pivot bushing on the breaker plate isn't worn out. Make sure the breaker plate ground wire is connected. How are your spark plugs? Is the choke opening up as the engine warms up?
 

73CobraJet

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Thanks but ignition is the first place I went. Replaced points and coil with Pertonix coil and ignition, all connections are new and secure. I’ve reading this carb 4300d is a real pain in the neck even back when new. Car after the same way with both set ups.
 

Sheriff41

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Have you replaced the fuel filter? If not, try replacing it and adding a larger inline filter. I recall a similar problem was solved when it was found that debris in the fuel line would clog the tiny filter, then would settle away from the filter element when the engine was not running. Also, verify your fuel pump is delivering the fuel at the right pressure.
 

Hemikiller

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The 4300D was always a problematic unit, along with the earlier 4300A. Lots of problems, not a lot of remedies. Those that really knew how to fix them are gone, such as Pony Carbs and KP Carbs. There may be others, I just haven't heard of anyone yet.

Something to keep in mind is today's gas is formulated differently than that in 1973. Ethanol can play havoc with the calibration of any 50 year old carburetor, so if you have non-ethanol fuel available in your area, a test run with a tankful may be worth a try. It may also simply be that the carburetor needs to be rebuilt. They are somewhat complex, but if you're organized and follow the factory service manual step by step, it's definitely a doable job for the average home mechanic. Cleaning the passages is critical, they have to be spotless. 73 also has the EGR system to contend with.

My 71 Country Squire has a 4300A on it's 429. When I bought it, she could barely make it up a long grade near my house, all the while billowing black smoke like a freight train. I rebuilt the carb with a kit from Standard, blocked off the auxiliary fuel inlet valve (a known problematic part), and lowered the float level 1/8" from factory settings. The difference is amazing in that it runs incredibly well now. I still have cold start issues with the choke, but that is a minor problem in comparison.
 

73CobraJet

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Have you replaced the fuel filter? If not, try replacing it and adding a larger inline filter. I recall a similar problem was solved when it was found that debris in the fuel line would clog the tiny filter, then would settle away from the filter element when the engine was not running. Also, verify your fuel pump is delivering the fuel at the right pressure.
I think that was going to be my next step. Don’t think it was the fuel pump. Bought the car in ‘19 and ran great for the first two seasons In ‘21 it went south but did not have time to work in it. Thank you!!
 

73CobraJet

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The 4300D was always a problematic unit, along with the earlier 4300A. Lots of problems, not a lot of remedies. Those that really knew how to fix them are gone, such as Pony Carbs and KP Carbs. There may be others, I just haven't heard of anyone yet.

Something to keep in mind is today's gas is formulated differently than that in 1973. Ethanol can play havoc with the calibration of any 50 year old carburetor, so if you have non-ethanol fuel available in your area, a test run with a tankful may be worth a try. It may also simply be that the carburetor needs to be rebuilt. They are somewhat complex, but if you're organized and follow the factory service manual step by step, it's definitely a doable job for the average home mechanic. Cleaning the passages is critical, they have to be spotless. 73 also has the EGR system to contend with.

My 71 Country Squire has a 4300A on it's 429. When I bought it, she could barely make it up a long grade near my house, all the while billowing black smoke like a freight train. I rebuilt the carb with a kit from Standard, blocked off the auxiliary fuel inlet valve (a known problematic part), and lowered the float level 1/8" from factory settings. The difference is amazing in that it runs incredibly well now. I still have cold start issues with the choke, but that is a minor problem in comparison.
The carb looks brand new, but I will look into
it. Last think I wanted to do!!!! Thank you!!
 

ROCKET70

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73 MUSTANG GRANDE Q CODE
My brother has a 72 Torino Q code and rebuild the carb twice still would not run right so he purchased a Edelbrock carb about 13 years ago and has run great since. He said it was a lot stronger with the Edelbrock.
 

Grabberblue72

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Hi all, I'm having issues with my 73 CJ carb. The car seems to start and run fine but when driving once in a while it seems to cut out a bit. The second issue is when I just run the car in the garage it will run for a bit the the idle seems to just drop off and eventually just die. Not sure what to look at as I have Holley carbs or the Autolite carbs all these years. i really do NOT want to take it apart!! Any help would be appreciated. Thanks. Also thinking about going Fuel Injection or Holley spread bore. Any thought on the least intrusive FI system. Dont want a whole lot of return lines, lots of computer stuff in the car. Don't want to drill holes in a Q code!!
I also have a 351 Q in my 72 convertible. Replaced it twice with NOS carbs. A good friend and a great Ford expert told me just put and Edelbrock on it , do not adjust it , the pluming is different so it took a little longer. That was 12 years and not one issue. In a show the carb is not visible under the air cleaner.
 
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Have you tried cleaning out the air bleeds? They are small brass plugs with very small holes in them. Open the choke and look down the front side of the choke housing, you will see them. Use some spray carb cleaner and wear safety glasses. If that works, or doesn't, run a good fuel system cleaner, like BG 44K, through the system. Current "gasoline" is a witches brew of all kinds of chemicals that carburetors just don't like, especially if the car goes unused a lot. Chuck
 

73StangJK

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I'm looking for my main carburetor post over in Stangnet. I used to be very active on that site. Lived and breathed the Stang. I'll find and link it here.

I really like the Edlebrock carb because it's easy to tune. But, it does not like that ethanol blend. Can't keep the fuel bowl needles from leaking.

Check out this site. It's got a pretty good manuel for the edelbrock/carter carbs. http://www.edelbrock.com/automotive/eps_intro.html#contents
 

jdomke1

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1972 Mustang Mach 1
4300D’s are temperamental. Like Hemikiller noted, the best know rebuilders are gone. There are still some good kits. Mike’s Carburetor Parts is a great source with very detailed rebuilding instructions. New float needed with todays fuel. Walker makes a great kit. These are complicated carbs that work great with dedication and drive you nuts without. Most issues as I recall were rough idle or stall when engine is warmed up. Especially when coming to a stop. Nothing more annoying then stalling at the stop signs. I’m dedicated to mine and refuse to take the easy way out and switch to Holley. I love those butterfly secondaries. Of course I did take 1/2 year of engine performance and carb rebuilding training back in the mid 80s. It was in high school in Dearborn sponsored by Ford. We tore down and rebuilt dozens of carbs over the course.
 
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