I am with Campbell on this one.  I have had a miserable time with Dickey John, Raven controllers and those idiotic ground drive pumps because of the plugged orifice.  If it plugs once, keep checking it.  It will plug again.  The vapor knives were mentioned also.  They can cause the same trouble.  Try to notice if they "smoke" when you pull the knife out of the ground.  Generally it will still function on one knife, but your problem sounds more radical. So, I am staying with the orifice.  70 lb.s should be an easy target, especially with warmer weather.

Now, what I want to know is, did you convert your rate to the English measure just so Americans could understand you better, or is that one of the things that didn't get changed to metric yet?  For what that stuff costs, we should be able to measure it any way we darn well please.