1968 J Code Owners

[robert campbell]

Dudes,
I ran into a bit of a challenge with Bill Norman's J code GT/CS with a 4300 on it. It is not the original carb, and has a cast number of C8PF V on the carb body by the front left carb stud.

I inspected and set up the carb in my shop and dialed it in on his car. It runs fantastic in my mind. It has a solid 20 inches of vacuum at hot idle, but will not idle down below 900 rpm which is a bit much for his automatic, but the car is actually very tight and does not clunk at all shifting from park into gear.

He has the proper gasket under the carb spacer and it does not demonstrate any kind of a vacuum leak. The vacuum is rock solid and does not miss. This is not a vacuum link in my mind. This carb does not have a secondary throttle plate stop screw like a Holley or even a 4100 does.

After decoding his C8PF V cast number internet sources say it could be on basically any engine of the era. Including the 429, 428, and the 390. Also a 351 and 302. I have some reservations that any one carb could fit all those cubic inch engines. Seems that the idle circuit to support a 429 would be far bigger than a 302.

That said, could you J code owners look at your carb base and send me your cast number? I want to see what we get.

Rob

 

[Mosesatm]

Rob,
What’s the Venturi size? 1.01?
Here is the only photo I have from the original carb on my previous J-code that you rebuilt.

 

[TraveledGTCS]

Hi Rob,

Before you ask, here is a photo of mine

Bill

 

[robert campbell]

Arlie, good call!! More research shows that there was a 1.01 440 CFM and a 1.25 CFM version of the 4300. Bill, it would help if you can pull yours off and measure the diameter of the throttle plate with it upside down. The pictures you have sent are not any help. I have Bill's cast number and would love to see a few more for more research. Again, they are low on the carb close to the front stud hole on the drivers side that mounts the carb to the manifold. If Bill's is a 1.25 diameter 600 CFM version it may be wrong for his car and engine.

Rob

 

[franklinair]

So, what is the correct venturi size for a 302 4300 carb?

Neil

 

[rvrtrash]

Rob, I know my factory carb was C8ZF, but I don't remember the last letter. Sorry. Take a look at the front or left front of the carb body. If memory serves, there is a number (raised casting) that gives the venturi size, so you don't have to pull the carb off and measure it.

Steve

 

[Ruppstang]

Here are some pictures of the C8ZF-D on the 68 GT350.
Rob you should remember it.

 

[robert campbell]

So, what is the correct venturi size for a 302 4300 carb?

Neil

Dad,
I would say the 1.01 that has 440 CFM.

Son

 

[robert campbell]

Rob, I know my factory carb was C8ZF, but I don't remember the last letter. Sorry. Take a look at the front or left front of the carb body. If memory serves, there is a number (raised casting) that gives the venturi size, so you don't have to pull the carb off and measure it.

Steve

Thanks Steve! Guess we are looking for a 1.01 or a 1.25 somewhere on the carb body.

 

[robert campbell]

All,
C8ZF-D seams to be the correct carb for a 1968 J code 302. It has a 1.01 venturi and 440 CFM. I will look at my cores and see if the 1.01 is stamped on the carb in some area.

Rob

 

[Mosesatm]

All,
C8ZF-D seams to be the correct carb for a 1968 J code 302. It has a 1.01 venturi and 440 CFM. I will look at my cores and see if the 1.01 is stamped on the carb in some area.

Rob

I think it’s on the butterfly.

 

[robert campbell]

All,
No joy on the butterfly. The measurement for 1.01 is at the top of the venturi easiest to measure with the top of the carb off. Butterfly is in the throttle plate and much bigger.

BUT, not to worry. Rob has developed the "Ronco 4300 Venturi Measuring Tool"!! This new tool allows the measurement of the venturi size on the car! The Guiney pig carb I have is a C8AF-AS 4300. One of the site members donated to me for use in the future. Can't remember who?

The difference between 1.01 and 1.25 will be obvious with this gauge for a mere $19.95 plus shipping!! Order now and I can provide a 1.25 gauge for 5 dollars more if you call in the next 5 minutes.

All kidding aside, this works great to identify a 600 cfm 4300 from a 440 cfm 4300! Check it out.

Bill, you need to do this or bring the car over. I could rebuild the C8AF-AS for your use. It even has the carb tag.

Rob

 

[Mosesatm]

Rob,
According to this article the venture size is found only on the bottom of the carb.

 

[robert campbell]

Arlie,
Not sure if there are more pages, but the venturi size, not the throttle body gasket is the "size" of the carb venture that corresponds to 1.01 or 1.25.

What I was trying to do to help Bill was an easy way with the carb on the car to tell what size his venturi is without tearing it apart. With the top off the carb it is a piece of cake with a simple ruler.

Rob

 

[Mosesatm]

http://www.mustangandfords.com/how-to/engine/1504-how-to-rebuild-the-autolite-4300-carburetor/

 

[rvrtrash]

The venturi size casting is in different locations on different series carbs, and I don't remember where it is on the square bore 4300. I thought it was front center but I guess it isn't. Here's pics of a 2100 and 4300D.

 

[robert campbell]

Again, great info, but trying to help Bill without taking the carb off the car or disassembling.

Rob

 

[CougarCJ]

C8PF-9510-V Autolite 4300 is a service replacement carburetor for a passenger car with Q code 428.

 

[TraveledGTCS]

Rob,

Did my measurement and it is 1.00." Also sent an email to you.

Bill