Husqvarna 455 low compression

I put a new prime bulb in and while I was at it I replaced the drive sprocket and clutch put in new air filter and spark plug. Now really low compression. Won’t start. What did I do wrong

Spark plug is most likely problem. Did you use a quality ngk plug?

Did you tighten the engine bolts in a star pattern. Try doing that after a teaspoon of motor oil into the spark plug hole. To help lube all moving parts. Then check your compression. Compression has to be 120 and up ok

Is compression release engaged? What is compression at?

I would suspect a faulty compression release.
A primer bulb, even missing, won't affect compression-Nor will clutch replacement (or lack of a clutch).
 
If you can post the full  model # so we can look up your specific model:
https://www.jackssmallengines.com/jacks-parts-lookup/manufacturer/husqvarna/chain-saw 
 
Looking thru the exhaust port (muffler removed) for any scoring will indicate 
the general condition of the internals.. Any decent scoring will (up and down on piston/ cylinder)
WILL lower compression..
.
IE, A Stihl MS201 with a scored piston / cylinder
 
 

Let us know what you find, I'm curious I like to know what does something like this so I can help others in the future.