I own a Ridgid pressure washer 80701, Subaru engine. It wouldn't start, took out spark plug cleaned off carbon deposits checked the gap and replaced. Checked air filter, oil level, gas all are fine. It started, pushed choke up and then started humming good, then let run a little. Earlier I let I had air out of hose releasing the trigger before I started the engine. Now with engine running I pulled the trigger handle on the wand and it cut out. Started again, choke closed moved it up ran a little then cut off. Now it won't start. I think I need a new spark plug, but I cleaned it with my wire brush, did all right. I performed the proper maintenance. What could it be?