Carb I chose for the work truck (390 Ford) was Edel 650 AVS. I live at 4500 ft, so I used the tuning booklet that comes with the carb to change jetting to compensate for altitude. The engine ran way too rich even after leaning out for the elevation. So what to do? Decided to spend aoubt $100 and bought Edel 02 sensor from Summit, its not a fancy one, just has a row of lights that tell the fuel air mixture ratio.
So sure enough, the mix was way to rich. So bought jets that had lots of metering rod choices, and started leaning the primary mix. Finally got the idle, accel nozzle, primary and secondary mixtures pretty close. Engine ran good, but just off idle (the transfer ports), when you first accelerate, the mix was not gradually going leaner, it was going lean real fast, which caused the engine to stumble with slight hesitation until about 2500-3000 rpm where the primary jets take over. So tried hanging small diameter wires in the idle air bleeds to richen the mix. Worked ok, but messed up the idle mix and idle speed too much. So decided the rectangular transfer slots could be enlarged, they are located just above the round idle ports. Have to open the primary throttle plates a little to see the transfer slots.
I used my small set of drill bits to measure the slot width, which checked out at 0.030 inches wide. So how much to increase??? I guessed at trying a 10% increase, so hand drilled the slots out to 0.033 width. It was easy to do since the carb housing is aluminum.
The engine now runs very well, almost perfect. With changing weather for winter, I'm just going to drive it some and see what I think. But it runs and accelerates much much smoother than before. I may tweek the pump shot, and may widen the transfer slots slightly more to 0.035 ( my next larger drill bit). For now much improved performance.
The carb I've chosen for my 360 Challenger engine will be an old 850 cfm Thermoquad. My 340 duster had one stock from the factory. For street use it ran great. That carb had to suck up all sorts of crap in the gas, and the carb would just keep going. Maybe not the flat out wide open throttle performance of a Holley, but great for street use. I"ll use the Edel O2 sensor to tune it. Hope this helps.
