I didn't know Honda (or anybody) made 4 stroke trimmers. My dad from whom I inherited the Echo (it was given to him) thought that was four stroke which is why it seized

. I managed to unseize it by putting a screwdriver down the spark plug hole and giving the top of the piston a tap with a hammer. It has carried on working for 25 years since although has always been a pig to start. The Echo was a commercial quality trimmer given to my dad by my brother-in-law who was a mechanic for a grounds maintenance company (he probably nicked it), unfortunately he has now retired.