Cyl #2 & #3 don't fire. All others cyl fire. All cyl have 145 to 150 compression. Have spark on both dead cyl. Have switched cap, wires, & plugs with same results. Thought vacuum leak or cracked intake so I plugged all vacuum ports with no improvement. Replaced intake with different one and used composite intake gaskets for better seal same results. Heads had valve job done before problem. Even put adjustable rocker arms on thinking some of the stem heights were not to spec. Valve springs all look ok. Any suggestions what problem could be before I pull heads to have checked again.

 

Long shot, but maybe intake valves aren't opening? You got compression and spark, only thing left are fuel and air. Or maybe big vacuum leak on runner to 2 and 3??

 

what are you working on ??

 

What is your distributer? If stock points maybe bad lobes on distributer... just because you have spark outside possibly under compression its not sparking... could be marginally weak spark, just a thought.

 

assuning you have a v8 350-455 you have compression,you have spark and it does run so you have gas,2&3 are on same runner in the intake so that would point me to a vacuum leak.get it running and spray some wd-40 around the base of the carb and along intake to see if they start firing.