and my mag check might indicate a minute or two of aggressive leaning is necessary to clean the plugs
THe question arises of how long do you continue running up an engine at high power in an attempt to reduce an out of tolerance mag drop caused by fouled spark plugs?
The longer you run the engine at high power, the hotter the internal temperatures get although the CHT gauge, if you have one, may not show much of a rise. But keep in mind, the hotter the engine, the less power it delivers during take off and if in a twin you have an engine failure at a critical time, the already hot engine that you have beaten to death during its run up - will deliver you significantly less power for single engine climb.
Extract from the book "Fly The Engine" by Kas Thomas. Chapter 3, page 41 and 42 on Run-Up's: Quote in part:
regarding plug fouling and mag drops:
"First use common sense. Try a quick burnoff of the plugs. The key word here, is quick. Don't take all day. Run the engine up to runup rpm, or possibly 100rpm higher, with both mags online, and slowly lean for best rpm. Don't be afraid to lean aggressively, because at runup power your engine is putting out, at best, only about 40% power and at that kind pf power setting you aren't going to hurt anything by overleaning. Leave the mixture at the best rpm setting for about 10 seconds. Lean slightly more until the engine just starts to stumble, then enrichen and recheck the mags.
If the "bad" mag still sounds bad and still makes you nervous, by all means taxi back. Don't sit there running up, straining on the brakes, kicking up the dirt with the propeller etc needlessly. If a 10 second burnoff won't do the trick the first time, the odds are it won't work any better the second time. All you will do is overheat your engine. Which brings me to another tip:
Always face into the wind for run-up (to aid engine cooling) and open the cowl flaps if any. If there is no wind, taxi to a position downwind of any available aircraft and unless blowing dirt is a factor - face into the other plane's propwash"
Unquote.
It is common to see pilots running up both engines together in a twin. There is no compelling reason for this and forget the myth about nosewheel assembly twisting. What is the point in banging away at high power on one engine while trying to burn out plugs on the other engine that is being tested? Same applies to prop pitch control exercising. One engine at a time please.. Leave the other engine idling leaned out waiting it's turn to do it's stuff. Stays cooler that way. The cooler the internal temps the better chance of safer single engine performance during take off climb.