I have a carter avs carb (4734S)on my 70 challenger with a 383 automatic. The carb is new with no vacuum or fuel leaks.

It runs excellent except it has a surge condition at highway speeds (above 50 or so). The current step up rods are .065/.064/.055 I have read a lot on various web sites and from what I gather this is a lean condition. From what I have read it seems that the original 3 step rods are pretty hard to find. I see many references to changing the step up springs and/or changing the rods to use the 2 step edelbrock versions. I have not seen any specific recommendations of which rods or springs to use or how to determine what rods and/or springs to start with. Is there any chart that shows the equivalent parts or a starting point.

The car has no idle or acceleration problems.

I would appreciate any help anyone here can provide.

I'd convert to the Eddy rods/jets & go to the Eddy site for the strip kit that has pretty close to your current diameters for cruise/power but slightly smaller and not sure exactly how much smaller dia to start with but maybe several thou or so smaller on the "cruise step. I have a pair of 3 step rods that are .0635" on the cruise step which might not be enough enrichment to help you. EDIT any possibility it's a fuel delivery issue at the offending speed/load?

Change the primary jet up one size, remember that the original Carter jets where in .003 increment on the diameter. IE a 16-391 is .091 diameter, the 16-395 are .095 diameter One other thing is on the original Carter jets with the three step rods they had a raised up shoulder on the primary jets, not flat like the two step and secondary jets are One other solution is to reduce the diameter of the intermediate step on the rods, I know racers who use to watch TV while using a piece of very fine sandpaper to tune up the meterting rods to meet there needs Use a good set of dial calipers or a good micrometer to get it right Sand a little, measure a lot

Thanks for the responses guys. I don't think that it is a fuel delivery problem. If I give it a little gas it is quite responsive. And a large amount of pressure on the pedal leads to a quick acceleration with no bog at all in either case.

Would changing the springs have any effect on my problem?

Thanks

The springs set the vacuum level (in hg) that you're into the "power" end tip of the metering rods & you would not want them there under high vacuum cruising but part throttle operation that put you into the smaller/richer intermediate step may help though but it sounded like minimum throttle highway cruising is when there's a problem. I would imagine a stock AVS has a pretty high vacuum # for them (weak tension). I found another set of 3 step rods & was hoping they'd be smaller on the cruise step but they too are .063-.064" . I could send em to you & you could sandpaper down the "cruise" step & see if that alleviates the problem & if so convert to Eddys & go richer with their selection of rods/jets & springs also

I want to give a huge thanks to RapidRobert who offered me a set of richer metering rods for free as well as provided free shipping. I put them in my car and it runs excellent. It's good to see that this hobby brings out the best in everyone. Thanks to all who chimed in with advice. Without it, I would still be struggling to get my car straightened out. I'm rather new to the hobby but read these forums whenever I get a chance so I can learn as much as possible from all the knowledgeable people on here. Thanks again Robert.

Michael