Simpson AlH3228/Honda GX200

My main question is, what are the max RPMs these can run at?  I looked at the manual, but couldn't find it.  It's a GCBUT if that makes a difference.  I want to know if this is all normal or what. 
 
I bought that power washer a couple years ago and it's been giving me fits since day one.  It was super hard to start for the first 10 hours or so.  I have to turn the throttle way down to get it going, but have it fully choked.  It's got a cat triplex pump on it. 
 
It shakes like nothing I've ever seen between almost dying and full throttle.  In either of those it's OK.  I don't mean shake like it moves some.  I mean eventually dance 30 feet across a hard surface until something stops it. 
 
Today I took out my small engine tach to see what it was running at because it just sounded too fast to my untrained ear.  Plus it backfires every time you let off the trigger and randomly ever minute or so when you run it.  I don't use it much, so I never decided to take a look at it.  7100 while having the trigger pulled and 7600 without.  If I put the throttle up all the way, it goes over 8k.
 
When it runs relatively smooth, the rpms were around 5k.  Below that it seems to want to die. 
 
Does all this seem normal?  What should I look into?  I don't know much about pressure washers.  Thanks!  Also, I drain and run the fuel out of everything in the winter and never leave old fuel in carbs of anything.  So if somethings wrong I didn't gum it up.  Thanks!