Are you using a white colored nozzle… like comes with it from the store? If so, i think those are too much pressure.
Here is a nozzle chart. Pick what PSI you want, go down the column till you get to 4GPM (or as close as you can), and that will be what nozzle you want. If you wanted 700 PSI, go down to 4.18, and it will be a #10 nozzle. If you wanted 1000 PSI, go down to 4, and it will be a #8. Etc.
Generally people say cedar needs 600-800 PSI, and yellow pine can go 1000-1500. More or less.
40 degrees is what most people use on wood, but you can use 25. This just means that a 40 degree will produce a wider fan pattern. So if you wanted a 40 degree tip that puts out 1500 PSI, you would go to pressuretek.com and order a 1/4" meg SS 40 #6.5.
