FE Misfire

[chopper]

OK, I'll take the initial shot. First a few questions: (1) Did it used to work OK but then this developed suddenly? (2) Any recent work around the time this problem developed? (3) What condition is the carb in? (4) Mechanical or vacuum secondaries? (5) Is the engine actually misfiring or are you instead experiencing small "popping" out of the sidepipes? (5) Are you sure the ignition system is operating properly, no loose connections, distributor advance operating OK, etc? (6) What condition are the spark plug wires in?

Now, a couple of suggestions. (1) If the plugs are white to tan, I would agree that you're probably running a little too lean. You might want to pull the primary jets and try one to two sizes larger. (2) Run a vacuum check on the engine with a good quality vacuum gauge to see what your idle and cruise vacuum readings are at stabilized engine speeds. Your power valve should be selected to be 1.5 to 2.0 inches lower than your lowest steady state reading (this normally occurs at idle but not always). The standard rule of "1/2 of the idle vacuum" does not always work with these high duration camshafts. Improper power valve opening can possibly cause erratic fuel mixture through the power circuit in the Holley. Most of the Holleys seem to come with 6.5 power valves. but Holley sells them in increments from 2.5 to 12.5 so you need to be sure you have the correct one. (3) If the problem is manifesting as an occasional "popping" out the sidepipes, check to see if you have any leaks in the exhaust system; this is the most common cause of exhaust "popping" at cruise and especially during deceleration. (4) If you have the vacuum secondaries, try to determine when the secondaries are opening. This is sometimes difficult, but if the secondaries are opening too early, this will also affect the fuel mixture getting into the cylinders. Holley sells spring kits to tailor the opening point of the secondaries. They also sell "quick change" kits which replace the top of the secondary diaphragm housing with a plastic cap which can be easily removed (without disassembling the rest of the carb) to change the springs for tuning purposes. (5) If all else fails, call Bill or Lewis at Southern; that's what I do. Hope this helps.