Ignition is Pertronix. Replaced the one I had used for years with a new one with the built in rev limiter. Same problem. Mummert heads with the provided valve springs have very few miles on them. Doubtful they are the problem. Will look at plug gap. Set them at Mummerts recomendation as I recall but don't rember what it was. Have replaced the plugs once already with no fix. May try tghter gap. Should get generator back next week. Guy had to order a new armature. Will tinker some more next week.

Are you still running points in your distributor? If so maybe you are having points bounce.

I’m with John in that a weak valve spring could be rearing its ugly head.  Do a quick visual for a broken spring then do a simple press test to determine if one of them is simply ‘weak’.  I have lever with a gauge on it to check valve springs on the vehicle with the rockers in place.
 
You don’t mention what your spark plug gap is and if too large, that could also be a contributor.  As a general rule for carbureted engines, 0.035” max for the spark plug gap and as the compression ratio and/or the fuel mixture increases, then decrease that gap number even further.  I’ve run as small as 0.022” gap for boosted applications.  A spark plug breaking down under acceleration or load is also a consideration.

Lorena, Texas (South of Waco)

I have a high perfomance electric fuel pump mounted by the gas tank. The stock dual action fuel pump has had the fuel side gutted so it is just a pass through. The vaccum pump side for the wipers is still functional. Carberation is the factory E setup properly re jetted. Running a little richer on the primary side. Miss is definately ignition. I know what running out of fuel acts like. When I first put the E setup on it back in 1966 it would run out of gas when you got into 3rd gear. Had to add an electric pump then. Removed the stock pump at the time to avoid a ruptured diaphram from filling the crankcase with gasoline. Modified pump accompolishes the same thing and keeps the vaccum assist for the wipers. Ted was running the Mummert 4 barrel intake with a 750 holley if i remember right. I am hoping around the 400 horse range with the E setup. When I finally get it sorted out depending on what times it turns I may switch to the Mummert intake if I want more.

Haven't been around here long enough to know much about your vehicle. 427 hp @ 6,000 must be awful thirsty, Is your fuel delivery system up to par to feed it?

Cam is an Isky custom grind that Ted Eaton used in a build in the Y Block magazine several years back that I basicly coppied. He was geting around 427 hoursepower at 6500 with it. It is streeet driven. I push it to 6000 or more if I can ever get it there, when the mood and road conditions allow it. Miss starts at 4000. Havent had it over 5000-5500. Still missing but seems to be a little better with more miles on it.

Is the car street driven?   How often do you run it at 6 grand?    From what I've read in the past, generators don't charge at lower rpm's.   So if you slow it down in a street car,  will you turn it fast enough to charge?     Your miss is at 4,000rpm only?   Or does it start at 4,000 and continue with the higher rpm's?

Just out of curiosity what cam are you running. Most would be laying down earlier than that.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

Valve springs are the ones that came with the Mummert heads. Shouldn't be a problem. Will look at my dwell tach. Not sure how high it reads. Dropped off the generator at repair guy today. Any ideas where I might find a larger generator pully? I'm thinking 6000-6500 rpm may not be good for my generator. Later Hi Po Fords used a larger pulley for a reason.

Do you or any of your friends have a dwell meter? Usually they have a tachometer function built in. It is an easy way to get a rpm reading to compare your other two tach readings to.