not totally sure where to post this but her i go 86 iroc with early 70's 350/5 speed.car was running ruff when idleing but great in the 3000+rpm range.well was getting a little tired of keeping it a lower gear going through a speed zone ( 3rd gear in a 30 4th gear in 45) pulled the the pluges to make sure ever things was good there and there was the normal color in 1 and 2 pluges(didn't check other plugs as these 2 are easy to get to)so i figured i'd look at the timing disconected the ets or is it est wire and to my shock dang thing was running at about 20*@800 rpm. backed the timing back down to 10* resest my idle to 700 rpm it now idels smoother and sounds a whole lot better now the bad news runs fine until i get to 3500 rpms then you can feel the engine dieing,doen't matter where throttle postion is ether.one problem i can think of is the cpu it pretty much disabled except i belive it still controls dist. advance and wasn't sure if the stock 305 chip would not be suitable for the 350's timing curve thanks in advance.

 

Is this a carbureted or injected engine?

 

sorry my bad it's carbed elderbrock 750

 

You'll never get it right as long as the OE distributor is in there. The computer is entirely incapable of dealing with that situation.

Get yourself a good quality (not just some junkyard unit) distributor with centrifugal and vacuum advance, so that the ignition timing under actual operating conditions isn't under control of the computer.

 

so something like this