The hot tip in diets now is low-carb and Atkins friendly. But when itcomes to carburetors and power, we're all in favor of loading up oncarbs and tuning them to work their best. To this end, we thought we'dassemble a stack of carb-loading recipes, tech tips, small partsrecommendations, and other suggestions for Holley, Q-jet, Edelbrock, andDemon carburetors that you can use to transform that lump into a leanmean, carbureting machine.
Many street Holleys like the PN 0-3310 750-cfm carbs come withvacuum-diaphragm controlled secondaries. If you've ever tried to changethe spring in these stock housings, you know how difficult it is to getthe rubber diaphragm lined up with the screw holes without tearing it.Holley now offers a quick-change diaphragm kit (PN 20-59, $12 throughSummit Racing) that eliminates the hassle with a sealed cover thatallows easy access to the diaphragm spring. You might also want toinclude a set of various diaphragm springs from kit PN 20-13 ($9), whichincludes seven springs from the lightest (white) to the heaviest(black).
We always like to start with the basics, so one of the best places tobegin is with float level. Holleys are especially easy to adjust. Allyou need is a 5/8-inch wrench and a large flat-bladed screwdriver. Toadjust the level, remove the sight plug from the passenger side of thefloat bowl, or just look through the clear sight plug if your carb is soequipped. Loosen the lock screw on the top of the adjuster and turn theadjusting nut clockwise to lower the float level or counter-clockwise toraise the level. The proper float level at idle is when the fuel justtouches the bottom of the sight-plug hole. Raising the float level makesthe engine run richer; lowering the level leans the air/fuel ratioslightly.
PV Wives Tales
For years, magazines warned the world that running a power valve with anopening point below the idle vacuum would dump all kinds of fuel intothe engine at idle, foul plugs, and waste fuel. The whole idea of apower valve is to allow you to run leaner jets in the main circuit andstill add fuel when load increases. The truth is that the power-valvecircuit is completely separate from the idle circuit, so if your engineidles at 7 inches of manifold vacuum and the power valve opens at 8inches or lower, the power valve will open at idle, but the engine willnot receive any additional fuel until the main metering circuit beginsflowing fuel out of the boosters.
However, if your carb is set up this way, with a low idle manifoldvacuum and high power-valve opening point, it will run rich atpart-throttle since it's likely that the power valve will be open muchof the time. So, the smart move is to install a power valve that opensat a lower point, such as 4 or 5 inches of manifold vacuum instead of 8.Your engine will be much happier and run much crisper under lightacceleration. There are 11 Holley power valves available with openingpoints ranging from 1 to 10.5 inches of manifold vacuum.
Holley has recently switched to the blue bowl and metering-block gasketsthat don't stick and tear like the old gaskets. You can buy themseparately in packages of two or as part of a rebuild kit.
Ever stomped on the brakes real hard only to have your Holley-carb'dengine stumble and die? When you're stuck in the middle of anintersection with a gravel truck headed your way, it's no time to havethis happen! This sometimes occurs when fuel from the secondary bowlsloshes forward, shoots out of the secondary vent tube, and floods theengine--stalling it. Drag racers often place a length of gas line overboth vents, but the cleaner approach is to use a vent whistle. Thesewhistles are often discarded during rebuilds, but the good news is thatby ordering PN 26-40, you'll get a 2-inch whistle for a mere $7 fromSummit that will solve that problem.