Carter 4738s Metering Rod Help

[schlett7nu1]

All
My 70 Challenger R/T 440 has it's original dated Carter 4738s carb.  It's always had a lean spot during light throttle cruise.  Over the winter I rebuilt the carb and noticed the metering rods are 12-241 with two steps.  I found a Carter document that suggests the factory rods for that specific carb are 12-575 three step (see attached page 19).  I obtained the 575 rods but haven't installed them yet.  Winter in WI means the car's not going anywhere until April.  As I understand it Carter had issues with the three step rods.  It may be why the rods were changed.  I confirmed the primary jets are per spec.  I haven't yet confirmed the springs.  Looking for someone who may have gone through this and settled on a jet, spring, rod combination for the 4738s carb that provides good all around drivability.  I'm not a hot-rodder.
thanks
Dereck

[anlauto]

Calling our resident carb expert.... @ScottSmith_Harms   

[ScottSmith_Harms]

I'm guessing here but It sounds like you might have mismatched parts. The Carters of the 60's/early 70's used a 3 step metering rods and matching jets. These were designed to offer a smoother transition when accelerating. The later 2 step design was used in later years. You can have problems simply changing out the 2 step rods for three-step rods without changing the jets as well, also the metering rod retaining caps are different between two and three step rods. So, what I would recommend is to either find an older Carter strip kit for your carb (ebay or a large carb parts supplier) or simply get a hold of www.Walkerproducts.com (they have a tech line) and order a new Edlebrock Strip kit for your carb and swap over all of your jets and rods for modern 2 step equivalents. The retention caps can be swapped for the two step style or the originals can be re-used with the 2 step style if you flip them over and fill them to level with epoxy.  .02

[schlett7nu1]

Thanks for the response.  I agree that someone likely did some part swaps in the past.  The car only has 28,000 original miles on it.  I was not aware the caps were different.  I did confirm the caps are stamped 65-60 (pump side) and 65-59 (opposite pump side).  I confirmed the primary jets are 0.101".  Both the caps and jets are what is listed in the reference Carter document for the 4738s.  The piston is not stamped so I can't confirm that nor can I confirm the springs.  I assume Carter had worked the specs out correctly for the application.  However, gas is now different.  As a start point, I'll work to get back to the stock configuration.  The kit you mentioned sounds like a good approach as well.  On a side note during the rebuild I found one of the brass floats had crush damage.  I bought two new brass NOS floats and confirmed weight and shape and re-established float height and drop.  I was only able to start the car and not drive it due to weather.  I'm not sure if that had an impact on the drivability issue I was experiencing.  I want to make one change at a time and assess.  I plan on putting the 12-241 rods back in and assessing the carb rebuild and float swap prior to making any rod, jet, or cap changes.
Dereck 

[RUNCHARGER]

The springs are critical of course because they time the enrichment. It sounds like you are going down the correct road with it. If it doesn't drive correctly I would buy the spring selection kit and compare the ones in there to the ones in the kit to try and determine what you have in there. You may need the kit to fine tune it anyway.
Probably the first step would be to get a vacuum reading as well to make sure it is within specs.
Finally, what is your elevation?

[schlett7nu1]

I agree regarding the importance of the springs.  I'll check vacuum in the spring.  15 degrees here today.  I won't be doing any operational evaluations until spring.  Elevation here is 840 feet above sea level.
thanks

[73440]

My 67-440 has a reconditioned original type Carter 4428 that I have ought parts from here : https://quadrajetparts.com/carteredelbrock-carbur-c-299_130.html?osCsid=let0ll08co1embprtqmsv3m5d7

Mine has a little stumble just before the next shift and I bought springs ,jets , metering rods etc etc etc to make adjustments but have not done that work yet to offer any help with your issue .

[schlett7nu1]

Thanks for sending the website.  I'll check out what they have.

[73440]

That book that is shown on the website is good also.

[73440]

These photos are the troubleshooting pages from the book.

[73440]

Parts bought from Quadrajetparts.com

[73440]

I have also bought from carbkitsource.com for Carter floats and repair kit.