Problem: I Installed A Big Cam, And Now My Motor Hesitates Off-Idle.
Solution: This is a very common gremlin associated with long-duration camshafts, but with diligent tuning it can be eliminated. The first step is to make sure the float level is neither too high nor too low, and that the idle mixture screws are set correctly. Likewise, the throttle blades should be angled properly in relation to the transfer slot, and the power valve needs to be matched to manifold vacuum. "If all of these preliminary diagnostics check out and the motor has sufficient initial timing advance, then it's time to modify the accelerator pump with a different cam and a larger squirter," explains Brown. "The idea is to introduce more fuel in a burnable fashion to go along with the big slug of air you just introduced to the motor after whacking the throttle. A four-hole spacer can help amplify signal to the carb, and shorter rearend gears can help as well."
Problem: When The Weather Heats Up, My Car Runs Like A Turd At The Track.
Solution: While no amount of tuning can make up for the thinner air that summer brings, rejetting to prevailing track conditions minimizes additional power losses that can result from running rich. The great thing about track tuning is that you're essentially on a dyno. "Since trap speed is an indication of power, just pay attention to what the mph does and don't worry about the e.t.," explains Van Noy. "Different wideband O2 sensors read differently, so they can't be an end-all tool. Tuning based on mph works every time. After you've achieved the ideal jetting based on mph, pull the spark plugs and they'll give you an idea of what to shoot for."
 Holley says that one of the...  Holley says that one of the biggest problems it encounters is people improperly modifying and adjusting the float level and idle mixture screws. Consequently, PNs 0-80457S and 0-1850S do not have adjustable needle-and-seat assemblies. "We wet flow and calibrate all of our carbs at the factory, so on a stock or mildly built engine there is very rarely a need to adjust those systems," says McFarland. |  Long-duration cams often require...  Long-duration cams often require uncovering too much of the transfer slot in order to maintain a steady idle. If your cam calls for exposing more than 0.025 to 0.030 inch of the transfer slot, cracking open the secondaries a tad or drilling holes into the throttle blade will allow sufficient idle airflow while minimizing the throttle angle of the primary blade. |  CSU's custom power valve allows...  CSU's custom power valve allows leaning the mixture at low rpm to prevent fuel from loading up, and opens at a preset boost level to provide fuel enrichment. The result is a smooth transition from low- to high-boost operation. |