dirty carb?

pishta, I too am going thru this with my slant six. Just put the car together with mostly used parts, thinking that the problem miss/engine breaking up under load had to be electrical. I replaced each part one by one with known good components.Rechecked all the wiring, only to still have the problem. On to the fuel side, "new" tank,pickup,fuel,pump,filter,carb. If I slowly run the rpms up (under load) to 4000 and then nail it not a miss till about 5200 rpm. If I nail it at 2800 rpm it will start to miss around 3200. So now it's on to fuel delivery, low float level,jetting, fuel pump not keeping up. Our problem sounds very similar. :banghead: Just a thought.