stunthanger.com
Engine basics => Engine set up tips => Topic started by: philip metzner on February 26, 2010, 09:59:25 PM
-
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.
-
Be careful with two-holers...they're probably not on centerline. The Fox spraybars for sure are not on center, and you need to have them below center, out of sight. Same probably for the DC Merlin.
Regarding adjusting your diesel...find a well experienced diesel user and get him to show you how to adjust the compression and NV. It's kinda subtle.
I did the right thing, and sold mine! Well, not the collectable ones. LL~ Steve
-
Were the spray bars with two holes desinged for the blade type needle valve?
-
If i set up the merlin with the holes out of sight, it wont run.
-
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'm starting to think that when i had it set outa sight, and it wouldnt run past the prime, i had something else wrong. I have set it up like you guys said and i'm going to the shop to test again. I have it running out the tank with it straight up and down, but the rpm isnt steady, and it sounds like its laboring.
-
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.
-
Thanks Jim, i now have it set like yours and the needle adjusts better. My starting procedure seems a little different than yours though. From a good running point i have to open the needle about half turn, and back off the compression a half turn. If i dont it will kick back on me. I prime a couple drops in the carb and a couple in the exhaust port. When it starts i have to turn the half turn back in to the compression quickly or it will quit, then i can turn in the half turn on the needle. It seems to run best with the needle about a quarter turn open from where it just starts to miss fire. Wile its running the compression adjustment doesnt leave much to play with. If i back off an eighth it starts miss firing, and if i increase an eighth it slows. Jim, if thats your super merlin on youtube, mine doesnt seem to run as fast.