I had my 1968 Chevelle 327 fully rebuilt (by a reputable professional machine shop) 5 years ago. It has been running great ever since. I stored it for the winter (as usual) but it ran poorly when I fired it up a few weeks ago. It was time for a full tune up, so I put in a new cap, rotor, wires and plugs. I converted to electronic ignition 3 years ago, using the conversion kits in Year One (so you can keep your original looking distributor cap) and never need to worry about the points. I uses Autolite 303 plugs, as I have had back luck with Delco's misfiring brand new. I tuned up the car last week, and it ran great, no misfires at all. This morning, it ran great, but after about 15 minutes, the misfire came back. It is not a steady miss, as sometimes it comes from the left or right bank, and it is random. I haven't had my carb rebuilt since the engine was rebuilt. Could that be it? Any help or advice is greatly appreciated! Thank you in advance!

So how long has the gas been in the tank and have you ever drained the tank? Storing a vehicle, especially in cold temps, causes condensation in the tank. Sta-bil in the gas helps but its not a cure-all. The gas can gel and plug up the carb/filter etc. May try a couple of cans of fuel system cleaner and fresh gas. Only put about 5 gal in.... that way it will be lighter if you need to drop tank smile.gif

When does it miss the most? Under load or idle?? What power source did you use for power to the distributor?? It may be that you are not getting a full 12Volts to it. Low speed will not show as bad a miss as high speed will. I don't think bad gas will cause the miss to move around on you like low voltage would. Just my .02 worth~ ;)