Performance & Hotrod Business May '14

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May 2014 n Performance & Hotrod Business n 69 not going to just install it straight out of the box and have a perfectly tuned and running engine. Say that three times to remember it. The most common call our manufac- turers face is about a freshly installed carb that does not perform perfectly. Maybe it's flooding. Maybe it's too lean. Don't auto- matically blame the carb before you take the time to tune it and check several other more-than-should-be-normal offenders. Smitty Smith from Edelbrock suggests some possible causes for flooding. One of these scenarios is part of the OE steel fuel line might have been cut off with the wrong tool, and some small metal shavings (barely visible) got into the fuel line. Another scenario is that the fuel line might be hooked to the front port of an Edelbrock style of carburetor, which is not the fuel inlet. This front port is for the PCV valve that has a hose from the front of the Edelbrock carburetor to its valve cover. Another situation that sometimes hap- pens is it will flood after starting the en- gine. He suggests removing the top lid of the carburetor, where there are only eight screws and two or three clips (depending on if it's equipped with a manual or elec- tric choke) and adjusting the float level on the carburetor. Demon's Scott Witmer suggests that the two greatest obstacles amateur carburetor tuners face are failing to understand the es- sentials of initial ignition timing and idle settings. A host of elements affect ignition timing, including fuel type, mixture strength, combustion chamber shape, compression ratio, tempera- ture, and humidity. Further- more, the ignition is always timed to fire the spark plug before the piston reaches top dead center (TDC) in the cylinder. Firing before TDC is necessary because of the time it takes for the flame front to ignite the air-fuel mixture in the cylinder. In the idle condition the transfer slots should give the appearance of a small square when viewed from underneath the base plate. Over exposure of the transfer slot at idle and insufficient initial ignition timing are the two chief causes of carbure- tor troubles. Stop Perpetuating Myths "In carburetor mythology probably the most misleading dogma involves changing jets in order to cure a rich idle setting," says Witmer. "Carburetor main jets are tuned solely to achieve one thing: the best perfor- mance at wide open throttle (WOT). Jets should never be changed to correct an idle impediment. Instead the idle circuit should be adjusted and the initial ignition tim- ing rechecked. Using a vacuum gauge, adjust each idle-mixture screw to its highest value. Keep moving around the carburetor, adjusting each screw an eighth to a quarter turn and waiting for the carburetor to respond." Edelbrock's Smith agrees. "We receive phone calls and people think (not knowing) that by changing and inputting a smaller jet into their carburetor, this alone will make the carburetor a smaller size in CFM. We explain over and over that this is not the case. It will allow the carburetor to run leaner (less fuel) and in most cases run better, however it will never change the CFM size. "One other common use or misuse, is installing a carburetor that is too large in CFM size, for example installing a 750 CFM Setting the idle mix on a Demon carburetor. (Courtesy Demon Carburetion) Carburetors are not plug & play; you'll need to make adjustments before you have a perfectly tuned and running engine. (Courtesy Edelbrock) PHBMAYp58-91.indd 69 4/2/14 1:58 PM

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