proper diesel needle setting?

I'm in the process of breaking in a PAW .35 (a serious finger whapper).

I'm finding in difficult to get the right needle valve setting. There seems to be almost two full turns between a bit too rich and a bit too lean. And it seems to have very little effect on the RPM (I'm using a tach). The compression seems to have a much greater effect on the RPM. Is this normal for diesels? and how do you find the best needle valve setting if watching the RPM isn't the best way? Go to just a bit too rich (or lean?) then back up 1/2 turn? Is it better to be on the rich side of the best mixture or the lean side of the best mixture?

Your diesel is running just the way it should. They are very insensitive to needle. Compression is the main control.

I would set the needle about 3/4 of the way toward the lean setting, and just leave it there.

For absolute maximum power, you keep leaning it out a bit, then tweaking the compression for peak rpm. At some point the engine will just stop suddenly, and you have gone too far.

However, for our purposes, you don't want to be on such a razors edge.

Back off the needle, and then tune the compression so the run just "cleans up". Then you have a reliable setting for stunt.

Until you hit a hot, humid day, then there is NO reliable setting, unfortunately.

LAST EDITED ON Aug-10-04 AT 12:12 PM (CDT)
 
The mantra you hear for diesels is that they should run with low compression and lean needle. There is an interaction between compression and needle setting. A rich needle setting adds to compression and a lean needle setting lessens compression. What I try for is to get a smooth run in level flight with no slow down or missing in maneuvers. If there is slow down in maneuvers then the engine is overcompressing. If there is missing the engine is too lean and undercompressing. Or something;)

If a diesel bites you, you have flooded and overcompressed it. Diesels flood much easier than glow engines, so you will have to unlearn some of your glow starting technique. Diesels vary; some need a head prime, others will never start if you head prime them.

Ron,
You might want to check out this site. It is a Canadian model club for diesel combat. They have an excellent information package on the care and feeding of PAWs and diesles in general...including break-in.

http://www3.bc.sympatico.ca/dieselcombat/index.htm