I have a stock 1979,no mods. It has new plug wires,fuel filter,and recent tune-up. It idles smoothly, and passed DEQ emissions test. Under light to moderate throttle settings it runs perfectly,smooth and strong. Under heavy throttle, the revs go up well,but it feels strained,almost like a flat spot around 4000. The secandaries kick in, but it lacks the punch the car used to have. Vehicle has 90000 miles and the carb has never been touched. Any ideas? Thanks

 

It has new plug wires...are they on correctly? Double check that. Pull the spark plugs themselves and see how they look. Replace if needed.

Others should chime in with some more ideas.

-Marques

 

Possible blockage somewhere in the exhaust system.. thermal reactors have been known to collapse internally even partially and down power, but you passed emissions testing... muffler could be plugged up

 

check the vcacume lines on the secondaries for leaks

 

does it make a strange sound under load? Like a dull roar that didn't used to be there?

My car has similar symptoms that I haven't been able to trace.