make sure the long spring is seated ok,you could take the slide out and clean it up with 800 grit emory paper,when you get the whole thing  shiney ,use rubber gloves to put it back in,try that.

You might have a sticking carb piston.
I had this problem in a different direction. The piston would not go up on acceleration. It was oil on the piston and bore. Once this was cleaned off, the problem was gone. This does require removal of the carb, but the cleanup is easy.
The oil issue could be from overfilling the oil sump, or the addition of the K&N air filter.
You can eliminate the overfilling problem by disconnecting the crankcase ventillation tube from the air box. Then you must plug the port into the air box with a capplug, and then put some sort of filter on the crankcase ventillation tube. The filter on the crankcase ventillation tube can be a sintered bronze air valve or compressor exhaust filter or equivelant.

SHE is fine now ( i think),put a table spoon of 2 stroke oil in and ran her 3 miles. today she is being a perfect lady!