Staying lean during runup?

[PilotAlan]

Maybe I missed it but I haven't seen anyone mention how a lean mixture would affect a carb heat check...

This.
If the mixture is too lean, you will either get no drop, or a rise (lean mixture + carb heat = richer mixture as the air gets thinner).

It's high out here (9000ft DA common in summer). Taxi very lean, you'll have to richen slightly to get the engine to 2000rpm. Richen to best RPM, then I add two full turn of mixture to get out of the red box.

At that point, carb heat results in the proper RPM drop. In my checklist, carb heat is the very last thing, making sure the mixture is properly set for takeoff conditions.

 

[MAKG1]

You have a "red box" at 9000 DA in a Cherokee?

 

[gismo]

Lance, there is also an argument to be made that there are quite a few people incapable of designing a fuel system

Can't argue with that. But IME most kit manufacturer do an adequate job there and without extensive flight testing manage to provide something that works as well as certified airplanes. And it's not like certified airplanes are 100% better in this area. Flight characteristics OTOH are often inadvertently or deliberately well outside certification limits on E-AB aircraft and without extensive (and expensive) flight testing as is done on modern certified aircraft that can come as a painful surprise to a pilot.

 

[gismo]

You have a "red box" at 9000 DA in a Cherokee?

And at runnup RPM???

 

[smccray]

I believe Lycoming issued an SB a few years ago stating that runups should be done with the engine leaned to peak RPM, not full rich, but I can't seem to find it right now.

 

[bnt83]

Suggest you look into Mike Busch webinars on the subject. If you like detail and accurate advice these should answer your question:

http://www.eaavideo.org/video.aspx?v=2274677932001

https://www2.gotomeeting.com/register/170496514

I hate to say it BUT you guys are seriously missing the boat not getting into the Experimental world of aviation. We are essentially leading the world in product development, performance improvements and many other areas of general aviation. The jerks in charge will do their best to make things more difficult and frankly I don't see the Experimental world lasting much longer in this over-control atmosphere from DC. But, hey, you never know. Maybe common sense will come back some day - just not holding my breath......

After reading about a few folk's experiences when they bought an already built EAB, I still am not convinced. Quality can be very hit & mis. It's eye opening when a new owner spews his frustration when he finds that the wiring was poorly done and wires are easily pulled from crimped terminals. With most of the EAB fleet flying on production aircraft engines, how "leading edge" advanced can they be?

 

[PilotAlan]

You have a "red box" at 9000 DA in a Cherokee?

And at runnup RPM???

OK, good point when the DA is that high. But most of the year you can get to 75%+ at ground level.

I'm not concerned about getting out of the red box at runup RPM, it's setting the mixture for takeoff power.
After the rest of the pre-takeoff checklist is done, I usually do a VERY short full power runup to get the mixture set right with WOT. Obviously only on good clean pavement.

 

[rcpilot]

I coarsely lean out right after start, richen a touch for runup, raise RPM and reset the mix after that.

I'm at 5000' though (and last time I flew DA was 7800'). If I were at sea level I'd probably lean after the start (just to keep plugs from being fouled) then go close to full rich for runup/takeoff, and definitely full rich with a turbo.