Riders Not Riding!

The rider rollers on my newly acquired Model 4 aren’t making even contact with the forms. On the front roller I can pass a piece of 12 pt card stock between halfway across the roller’s length. The back one is better but still light on the same (operators) side. The forms are accurately adjusted to .918. Their carriage blocks have been replaced with steel and nyliners. I thought that I might have a galley bed and the forms  were too low in their carriage to make proper contact with the riders. But my .918 gauge measures slightly higher than the bearer rails (not to mention that my impression seems right). I have checked to make sure the the top carriage is laying evenly on both sides of the bottom carriage and that the oscillator moves freely up and down in it’s slots. The oscillator sets evenly on the forms and in fact I have been able to run a dozen jobs by passing the rollers over the form while off impression first. What I haven’t done is check the rider’s bushings as I have not been able to remove the taper pins. There is a little bit of play but it seems the same on both sides. I checked the play on another #4 that I used to run and it is the same. What’s most telling is I set my top carriage on the bottom carriage and it was the same. I’m thinking that the carriage is tweaked. I’m not sure how to confirm or how to fix it. Thank in advance!