Hey guys I have been tunning my holley and its like night and day from the edelbrock I had, It just melts the tires till 3rd gear punching it from a roll, and man does it pull hard. Well my question is, I have a 750 double pumper and I have 74's in the front and 82's in the secondaries. Do you think thats to much of a difference or it doesn;t matter?? I had 76's in the front and it felt really strong also but it was a little rich on the A/F guage during cruise. Well what do you think? also any suggestions on wut color cam to use on the secondary accelerator pump to be tight at idle and extend the rod fully so I get the meax out of it? thanks

 

The actual jet "numbers" don't matter. Just give the engine what it wants. Tune the primaries for driveability, and the secondaries for best ET or MPH, or best A/F on the gauge.

Same for the accelerator pump. Basically, it's a designed-in crutch to make up for the lag in fuel delivery that carbs all suffer from, designed to cover up the period of time after you open the throttles during which air is flowing, but fuel isn't yet. Use a pump shot that's no bigger than necessary to get that done, otherwise you're just wasting fuel and getting nothing in return every time you touch the throttle. Your cash register just empties a little more with every motion of your foot but you get no more power or anything else. Make sure the pump doesn't bottom out (.015" - .030" of lever travel still left available after the throttles are wide open so that you don't bend or break parts), and that the duration screw is against the lever at all times. Nearly all Holley accel pump cams are too large out of the box, and they rarely require a larger one, posts you see here notwithstanding; people who don't understand how a carb works, jump directly to that before properly tuning the carb as a whole, and try to use it for something it's not intended for.

If it cruises rich, the primary jets are too large. Typically you will get better results by lowering them until you get to the right A/F ratio, either on the gauge, or by leaning them until it surges and then going back up; and then raising the power valve nuber to about 2" below the lowest vacuum you see on a vacuum gauge while cruising or otherwise normally operating the car without a demand for power, which will usually be idling in gear with an auto trans. It's impossible to predict what the ideal cruise A/F ratio should be, every engine and gear and converter and car combo is different; A/F ratio at WOT should usually be around 12.7:1 to 13:1.

 

Keep in mind at your power valve adds about 8 jet sizes to whatever jets you've got in there when it opens. So what? Well, those 74s in the primary side become like 82s when the power valve opens. Secondary side doesn't usually have a power valve so the 82s are always like 82s. Therefore, at WOT you're much closer to "evenly" or "square" jetted than you may think.