am having a similar problem.I have a '67 327 with edelbrock intake and carb, MSD hei distributor + wires, and headers.I will get it running good then I'll fire it up the next day and it's a dog.Recently it's back-firing when I let up on the gas while cruising but runs fine if I get on it also it seems a little sluggish off the line at times.

This may be a dumb question, but what is the best way to set the idle mixture?I too have the 1406 but manual choke.Not sure if this is the problem but I would like to double check.I recently rejetted and changed the metering rods with what edelbrock recommended when I moved to mich. from wyo (dramatic elevation drop) if that helps.It just seems that every time I fire it up it's running differently......damn gremlins!!