[elmariachi]

This is an entirely random event that I have seen happen in both 3rd and 4th gear when at WOT around 4500-5000. It is SO BRIEF, that the car does not nose over, slow down, hesitate, nada. Its not a crack (like an explosion) its truly a cough. Its not a cylinder miss, its an entire cough/cutout/backfire of the engine through the carb/intake. It lasts about as long as the snap of your fingers. And it does not repeat itself during the acceleration. It does not always happen and its not at one repeatable rpm. Totally random but always WOT and generally above 4k rpms.

So for example yesterday morning we had been out running for a couple hours. At one point I was running 55 mph in 4th as we entered a 2 mile straightaway. I downshifted to 3rd, floored it and took off. A few seconds later as it neared 5000 rpms, it coughed once but it remained floored because it happens so fast I didn't even have time to react and lift. I continued to acclerate up through 4th and into 5th and then I finally lifted at about 130 mph. Following that one cough, it never missed a beat until I lifted. And yes, I do lift to shift.

My MSD box is limited at 6200 and my engine stops making power at 5800 so its not an issue of the rev limiter. Wires are properly separated to avoid crossfire. Holley 3255-1 has metering blocks front and rear.

Valve lash was checked and set hot per Comp cam card 300 miles ago, no issues.

Rick, MSD 8594, blue springs, no issues there. I am already at 18 base timing and 36 total all in my about 3k. Remember guys, it DOES NOT do this with the Mighty Demon 750 installed, all other settings being equal.

I will stiffen up the vacuum secondary spring again and see what happens. While dialing this thing in I found the stiffer springs to induce a hesitation when the secondaries opened. Per Holley's instructions, I kept lightening springs until it went away, ending up with the lightest spring. I will unhook the secondaries altogether and see what happens.

Jerry, I was planning on chasing down a different set of bowls if nothing else produced a solution. I have an Innovate LM-1 O2 sensor that has been all but worthless but I plan on hooking it up and going out with the laptop and see what it sees when it coughs.

Thanks guys.