help needed

Been working on my 372 getting new crankshaft seals installed and now that I got it all back together my crank won’t spin. What could be causing this? Acting like it’s locked up and bogs my saw down when I start it. Any tips would help a lot, thanks

I have a McCulloch MacCat435 saw that I have been trying to sort out for a while now, but no matter what I try, the saw will only start if it is primed with the bulb, or if fuel is dropped straight into the carb. It will then run for a few seconds then die again. I have cleaned and rebuilt the...