Tim,
It will take a long, boring, frustrating, somewhat exicitng time before you make syrup, but, you definitly need to keep those plugs out to maintain proper flow. The good news is that once you do, it will have a much more frequent draw off of syrup than the "batch" method. It will help with syrup quality too. You aren't doing anything wrong and there probably is nothing wrong with the evaporator either. Just like a kid....be patient and good things will come....
Harlan
Somewhere around 2400 taps
3.5 x 10 D & G w/ preheater
CDL steam pan on the way
Kubota L4300, Redbone hound
2 sons have a 18" X 40" D&G wood fired for heating the sugarhouse and making their own. They sell cheaper than me........