I don't know what brand of solenoid valve you bought but I believe I can help you anyway. If you know how a solenoid valve works then you know that a small amount of air comes from the inlet and goes through a hole in the diaphragm to the top of the valve above the diaphragm. I had a similar problem to yours and i solved it by making that hole bigger. On mine, (it was green, orbit watermaster i believe) i just removed a little piece of plastic that was in the hole(some sort of filter i believe, but its for dirt when using the valve for water so it just restricted airflow). If you don't have this piece of plastic and just a hole you can just make it a little bit bigger, but not too much, trial and error might be a good idea. I hope this solves your problem.
This is irrelivent, but i just coated chapstick in plastidip.
I think that post right there would justify my answer. He has done nothing but ask questions for his entire stay (even though thats what most people do). It seems that if you wanted a new, contributing, member, he's not the one. And that wherehouse thing.....