350 SBC Nova Motor

The first thig I check when any engine isn't reving like it should is to have someone push the throttle to wide open (with the engine off of course) while I look in the carb to be sure it is actually opening the butterflies all thye way. You may have been on the right track when you suspected the valve springs. I have seen a lot of good motors go weak due to the valve springs. A common practice in Hi-Po SB Chevys is to install oil restrictors to limit the oil delivered to the top of the heads. This is all right to keep the rest of the motor from starving for oil at high RPMs. BUT the only thing that cools the valve springs is that oil running over top of them and carrying the heat away. Besides the heat from the engine (heat rises and the springs are on the top) valve High Performance valve spring generate a lot of heat themselves. if they get to hot they won't last long. Short bursts down the drag strip are one thing but driving around town can ruin them fast. A wise investment is a valve spring tester that can be used without taking the motor apart. You just have to remove the rocker arm, make sure the piston is down in the cylinder so you dont bend a valve and use the tool as the instruction say.