Change your jet size, if the jet is to large, to much gets injected. Another way to test this is by putting a push lock valve or Jaco valve on the line going to your manilfold, assuming your using 1/4 line it just snaps in place, close it 40 to 50% and test. I use the fittings in our business and put valves all over so I could disconnect lines.
Rick
Rick