Re: Help!!!427 misfire 2000 - 3000 rpm
I'd suggest richening it up and see if it clears...back in '83 I put a 69 396 BBC in my '81 D150(but I'm a Ford guy really :) and the new 750 holley I had on it would rattle at cruise only- easing up it was ok, but normal driving right about 2500 rpm it would rattle...never did mess with the carb- got horrid mileage, put the original quadrajet back on and quiet as a churchmouse. After swapping the carb I thought jeez- guess it was running way lean at light cruise, luckily the motor wasnt hurt, drove it daily @ 17mpg up till '93 when I bought a new F150...I didnt mess with it, but someone told me rejetting wouldnt help it was the wrong power valve switching from idle to power circuits...I dont know but guess holley has different power valves depending on what kind of vacuum you pull...I had a very mild cam on a fairly big motor so it pulled a very strong vacuum at light throttle, which I was told causes power valve to shut, returning to idle bleed circuits...I dont know, the only carbs ive really messed with are tiny little model heli carbs, and a few quadrajets ive had over the years...
an easier way to check might be to get it up to temperature, when its rattling, to make sure its not humidity/octane/fullmoon whatever related, and back the timing off about 5 degrees to see if it quits rattling- if it does she's runnin lean. the funny thing with mine was it would detonate with cheep gas/too much timing, but it was a totally different sound than the soft rattle at cruise I got- but same cause...if you cant find an ignition issue, might be worth a shot?
Confidence: that feeling you have just before you realize the mess you've gotten yourself into...