it was misfiring before but that was because of the air leak from the wrong fel pro gasket for the intake....engine shakes below 2000 rpm but again won't idle unless you hold the throttle down off of the carb....the shop I took it to did the initial break in at 2500 RPM for the 20 min time frame to break in the cam but they never took care of the idle because I am assuming I didn't ask....I can kick myself for not allowing them to start it up so I could hear it