HELP w/craftsman lawn tractor:no power

I have a 4 year old Craftsman lawn tractor, model# 917.289244. It has a 21 HP Briggs, model#331877 type#1371-b1. A month ago, after a no start situation, I diagnosed that the compression release mechanism on the camshaft had failed. I replaced the camshaft. In doing so, I found the pieces to the old one in the sump. most of them were rather small, not much left that was very big! I inspected everything and didn't see any damage from the disintegrated pieces. After putting everything back together, it starts and runs but lacks power. I can put it in gear and it rolls slowly. If I try to engage the blades, it dies. I was wondering if I did something wrong when putting it back together or was there damage I missed. It had enough compression to hold back the starter when there was no compression release. I have spark and I have fuel. I didn't mess with the carb other than to remove it and set it off to the side and then re-install. What am I missing? I guess I'm asking the community what would they look for before throwing their hands up and bringing it to the $shop$! Mower ran well before the no-start issue. It did consume a little oil and I would get some bluish/white smoke when mowing deep wet grass. I figured that was where the oil was going. But I never lost power. Any help would be appreciated. When I do have it running now, I don't have any smoke, but I cant put a load on it, when I do it dies.