[Bruce Edwards]

Valve springs can get over stressed when installed if they are "stacked" to get the retainer in place.
Just a thought, I am not saying that is the problem. Take a good read off the carb to be sure you have a nice steady reading.
Of course if your cam is really tall and has lots of overlap you will have a low reading.
Again sounds like you are on the right track. A test drive will tell you a lot more than a run in the driveway.