i have an 86 chevy truck with a 305 i built for it, crane 256H cam.  it feels like from 3000 to (well it never stops past this) it cuts out and has dead spots.  ( it just started this past weekend, only did this 3 times to try to figure out what was going on) i read the article about fuel reversion in the 383 build. i have a quadrajet and DID size the jets and it runs fine.  but i did not change any of the secondary components because the engine wasn't going to turn more than 5000 rpms ever, so i did'nt think i needed to, could that be causing this? it sounds like i may have preignition because it could be running lean, but i have never heard an engine with preignition problems.  can't really trust spark plug readings because it doesnt run in the secondaries all the time. its not ignition because it will rev up fine to 4500 without getting into the secondaries