The hot idle

Originally Posted by Walt

Has anyone installed the .025 nozzles with an O360? Don suggested I try this for the hot idle issue and perhaps enjoy better atomization at the same time, but pump pressures and fuel flow "may" be an issue. Anyone have any experience yet with this setup?

After talking with Don (he ran some numbers to ensure that I had enough pump pressure from the engine-driven pump to make full fuel flow at takeoff with the smaller restrictors), I installed the .025 restrictors about 6 weeks ago.

As far as the hot idle is concerned, it didn't appear to do much at all. My gut feeling (based on totally unscientific observations of ambient air temperature and temperature under the hood) is that it can now be a few degrees hotter before it starts to miss at idle. By "a few" I mean maybe 5-10. For this little of an improvement, IMHO it's probably not worth the $100 for the restrictors.

As far as better atomization goes, well, I'm not sure how to tell if it's better or not. The engine still runs LOP just fine. In fact, I can pull the mixture all the way to cutoff and the engine really never gets rough before it quits -- I notice a power decrease, but no real roughness. This was also true with the stock .028 restrictors in this engine.

Does anyone else know how to tell if the atomization is better?

The .025 restrictors did change the EGT behavior slightly, but that's probably to be expected. Changes were relatively minor -- things like which cylinder is the first to rise after application of takeoff power, which cylinder has the hottest EGT on climbout, etc. The absolute values of the EGTs at various stages of flight changed slightly too, but the values are relatively meaningless -- more important is where peak is and how far from peak you are.

Bottom line for me: My engine runs great with either the .028 or the .025 restrictors, except on the ground for extended periods of time when it's hot outside. I probably didn't need to spend the $100, but I'm not sorry I did it. Don's offered so much free help and advice here and on the phone that I was glad to send him some money.