Cams for Carbs
Most Holley four-barrel carbs use a typical accelerator-pump cam andsquirter combination that generally works very well. If you're intoexperimenting to improve your dragstrip 60-foot times, you mightconsider investing in an accelerator-pump cam assortment kit (PN 20-12,$20) that will allow you to tailor the pump-shot fuel deliverycurve--basically either more quickly or more slowly. Shoot for addingthe amount of pump shot that will accelerate your car the quickest. Youcan also work with accelerator-pump squirter size to trim the amount andrate of delivery.
An engine tuner once told us that 90 percent of all driveabilityproblems could be traced to vacuum leaks. If your street motor issuffering from part-throttle hiccups or the lean-surge blues, take a fewminutes to search for a vacuum leak, first make sure all the carb andintake-manifold bolts are tight. Also make sure all the vacuum outletson the engine are closed off and that all vacuum lines are intact. It'scommon to discover a rubber vacuum plug is missing or cracked. Ifeverything is secure, start the engine, warm it up, and shoot shortsquirts of WD-40 around the intake and the carb and listen for a changein idle speed. If you locate an area where the engine speed increaseswhen you hit it with WD-40, then you've found a vacuum leak. The enginespeed increases because the leak pulls the WD-40 into the engine andburns it, temporarily increasing engine speed. This can make a mess thatwill have to be cleaned, but it works to locate hard-to-find vacuumleaks.
A common knock on older Holleys was their easily blown-out power valves.Holley addressed this and made them much more durable. The company alsosells a power-valve check-ball kit (PN 125-500, $13) for all pre-'922300-, 4160-, and 4150-style carbs. The kit positions a small checkball, spring, and brass seat in the passage leading to the power valve.In the event of an engine sneeze, the check ball quickly closes,preventing pressure from damaging the power valve. All new Holley carbscome with this as a built-in feature.
The beauty of the Edelbrock Performer series carburetor is that you canchange the primary metering rods and springs without having to removethe carburetor lid. Using a small, straight screwdriver, loosen thescrew and slide the cover over to allow the primary piston and meteringrod to pop out. The Edelbrock carb uses a primary-jet and metering-rodcombination along with the step-up spring. Manifold vacuum drops as thethrottle is opened, and the step-up spring pushes the metering rod outof the jet, increasing fuel flow. You can fine-tune your engine byexperimenting with leaner or richer metering rods and also with variousstep-up springs.
Floats That Don't
One of the innovations applied to Q-jets in the '70s was a move to aplastic or nitrophyl float. These floats are easier to make, butunfortunately over time they have a tendency to absorb fuel, so after awhile the float is more like a sinker. The fix is to replace your oldfloat with a new one, like a direct replacement float from Edelbrock (PN1985 or 1985, $10). Also make sure to properly set the float level. Thisis a critical adjustment for all Q-jets.