Carter 9605 AFB-need help-light surge off idle

I have bought a '64 Merc with a 390 A/T and the previous owner installed a carter 9605 AFB. It starts and idles fine and cruises down the road good but in sub division driving just off idle it has an annoying surge as if there is a fuel delivery problem. On moderate or heavy throttle tip ins it is fine so accel pump seems to be working. I know little about Carter but have read that this is a tuner's carb and has many adjustable features. Any idea what I might do to solve the low speed/very light throttle hitchy feeling that is always there unless I tip into it?
Thansk in advance!!!!
Jim

 

The needles that control mixture are two-stepped, under high vacuum the rods are all the way down on the lean step, when the vacuum drops the rods rise and the rich step controls the mixture. What you might try is recalibrating with a rod that is thinner on the down position. An example, if the rod is a 7547, try a 7147. This is an edelbrock rod nomenclature, and the rods do interchange. In Carter speak it would be 16-241 for a 7147, I don't have all the rod numbers, but get a calibration kit for an Edelbrock carb and play with it. If you are satisfied with WOT performance just use a rod with lower first two numbers. Someone may know what your rods are if you post them, they will usually be a 16-**x in a Carter, but Edelbrocks will interchange. Weber was making them all from the 9000 series on and the Edelbrock is the same carb.

Also pull the top and check the float hieght, uneven floats are very common out of the box. I set mine to 5/16"-11/32" and 1 1/4" drop, though Edelbrock says 7/16". The float hieght affects the idle and off idle mixture as well as the accelerator pump.

Good luck.

 

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Too much initial timing or vac advance can cause a surge like problems, sometimes called fast timing bump. Re test your timing and try disconnecting the vac advance line and see if there is any positive improvement.

 

Sometimes the little Aluminum pistons that the metering rods are attached to get gummed up and dont rise and fall smoothly. If it's an old Carter (pre-Edlebrock) on a car that sat for a bit I've seen them get that chalky white residue on them. Check them out as well. Some #0000 steel wool and some carb cleaner will fix em up. Spray the bore they go in as well. Just something else to look at.