CARB TUNING 101:
Most people have trouble with Holleys because they don`t learn how to adjust them & they don`t run right out of the box ever!! They are far more adjustable than anything else but this is what screws up most people as they don`t understand what to adjust to get what result or what affects what other circuit in the carb.
1] Install the Holley carb & get it running as best as you can by setting the idle speed & mixtures, take any slack out of the accelerater pump arms by adjusting the spring loaded screw in the arm & make sure that the pumps don`t bottom out either @ full throttle
2] Adjust the float levels On most Holleys this is easy just remove the sight plug , loosen the lock screw & turn the nut to adjust , Counterclockwise raises the level & Clockwise lowers it , be careful lowering the level though as there is nowhere for the fuel to go especially in the rear bowl so lower it 1 turn or so take the car for a drive & recheck the levels. With the stock Holleys you will need to remove the bowl & adjust the level by bending the tab on the float that touches the needle & measure with a drill bit at to far end of the float from the pivot, the float should be 15/64 on the front bowl & 5/16 rear , be careful with the O ring on the transfer tube I usually place the O ring on the ewnd of the tube so it can roll on as the bowl is replaced, & make sure you have new gaskets if the carb is not new
3] Take a reading of the manifold Vacuum idling [in drive if it is an automatic] & install a power valve at least 1.5" lower than the reading you get , EG if you get 6" of Vacuum install a 4.5 power valve, if you don`t do this first no other adj will be right!! Now reset your mixture screws. if you have a 6.5 power valve & your vacuum is above 8" don`t change the power valve The carter has springs to adj this but on high perf engines sometimes the idle vacuum in gear is below 3" which is the smallest spring you can get, the Holley can be plugged off & then you upsize your jetting 8 sizes to compensate, there is no provision for this on a Carter.
4] Now take the car for a drive at a steady speed for 5 mins or so. Highway works great for this & you must have at least 2 new spark plugs installed, then shut off the car & pull a plug, you want it orange to tan in color ,adj your front jets accordingly [chocolate to black is too rich , white grey or yellow is too lean] Check your mixtures. Holleys have jets that size in less than 1 thou increments, the carters can`t do this with the jet rod combos.
5] Now make a full throttle pass & recheck your plug color to see if the plugs get lighter or darker in color & adj your rear jetting same as the front.
6] The secondaries on a Holley Vac secondary carb are adjusted with springs which are changed to a lighter spring until a bog is felt from the secondaries opening too soon you then install the next stiffest spring, & springs are available in a kit Or you can get the double pumper Holley & manully control the secondary with the throttle position. The Carter has a spring adj on the AVS & Thermoquad only, the AFB / Edelbrock have a weight that has to be ground down to adj this properly & you have to weld on to it if you go too far
7] Now you can adj the front accelerater pump, if you have an instant bog the shooter is too small or you haven`t removed the play/ slack from the pump arm , if it doesn`t bog go smaller until it does & move 1 size bigger to eliminate the bog. Carters shooters are difficult if not impossible to locate so I often have to drill them. Holley offers 10 sizes of shooters
8] If you have a bog or sag in power 1/2 a second after you hit the throttle [don`t open secondaries] you don`t have enough volume of fuel being delivered, this is controlled by the pump cams on the throttle shaft, Holley offers 7+ cams with 2 positions each so 14+ settings, again you want to use the smallest cam without causing a bog so not waste any more fuel than nessisary & to get the crisp throttle response.The Carters only offer 2 or 3 volume adjs by using the holes in the pump arm.
9] Then tune the rear pump [only if it is a double pumper] the same way only going to full throttle, the bog may not be possible to eliminate on the secondary depending on the stall of the converter, weight of the car,rear end gearing etc you may have to learn to snap the throttle to 1/2 open & roll in the rest quickly to prevent bog but you can still tune the rear pump to suit your driving style. Carter does not make a double pump carb so you are SOL!
*NOTE* all this will apply to BG carbs too, why anyone would own a BG carb is beyond me tho.
