I noticed the new nva's i bought a few years back for my fox engines had the two discharge holes instead of one. Why are they like that? I got a run on my little dc merlin diesel today and noticed its the same way. It seemed to adjust funny to me, but its my first diesel so i dont know how they adjust, or feel.

  Were the spray bars with two holes desinged for the blade type needle valve?

I noticed the new nva's i bought a few years back for my fox engines had the two discharge holes instead of one. Why are they like that? I got a run on my little dc merlin diesel today and noticed its the same way. It seemed to adjust funny to me, but its my first diesel so i dont know how they adjust, or feel.

Way back in the late '50s and '60s when I flew a lot of stunt, the two-hole Fox NV was OK. Look in the venturi, and rotate the back hole just out of sight to the rear. You will be able to see the front hole OK. That is the way it always performed OK for me.

Then I found something better. Using an OS or Enya NV, use small washers to center it and set up the single hole facing straight back just out of sight. That is the point of lowest pressure as static pressure decreases when the faster air flow -dynamic pressure- increases. It worked on Fox, Veco, Johnson and Super Tigre for me and everyone else that tried it.

I have a Super Merlin with the red head.  I peered into the venturi and couldn't see any holes in the spraybar.  When running your engine, you will probably have to increase compression to get it to start.  After it starts, back the compression off as it warms up.  It should run steadily and speed up to a point, then start missing from being undercompressed.  Compress it back a little, and fiddle gently with the needle.  It should speed up to a point as you lean out the needle, then start missing again.  Richen it up.  Break it in a little undercompressed and a little rich. Generally the more you run a diesel the better it runs.  Flying it control line, it should run smooth and steady in level flight.  If it slows in maneuvers, it is overcompressed,  If it misses in maneuvers, it is a hair lean.  The exhaust, with a commercial fuel, should be honey colored to clear.  The exhaust is fairly cool.  I routinely stick my finger into diesel exhaust to see what color it is.  if you do this with a glow engine,you will have a burned finger.