I am just trying to help out my Aunt here! She bought a Honda Accord about 3 months ago! They motor would do a "pluck pluck pluck" sound. She took it to the Mechanic! And the valve springs get stuck! They go down and get stock coming back up! Here a few pics' i am pretty sure those are valve springs.

 

Can't really tell from the pic's......to see if the valves are getting stuck, are you rotating the crank, like you would for a valve adjustment, and checking the clearance at each point for each cyl.... the tech might have done that. If they are getting "stuck", I hate to say it but that is a sign of possible bent valves.

 

Was engine running well when purchased? Is engine now missing? A compression check will show if valves aren't closing and which cylinder has problem.

Valves getting stuck due to carbon build up is rare. This valve train looks nice and clean. Hard to imagine carbon buildup being the problem.

good luck