Aerozepplin
Your level of knowledge is as little as mine (very low), but vastly higher than many others.
The ‘traditional’ method of leaning a basic carby’d piston aero engine demonstrates why the received wisdom is mostly nonsense.
As you know, the traditional method is to lean until the engine runs ‘rough’, and then enrich to remove the roughness.
The traditional explanation for the roughness is ‘lean misfire’: The mixture is apparently so lean that it’s very hot and causing all sorts of engine problems (including all that piston damage that yr right has to deal with). Enriching the mixture removes the ‘roughness’ and restores the engine ‘safely’ to rich of peak.
In fact, the ‘roughness’ is caused by an imbalance in the fuel/air ratios being delivered to each cylinder, resulting in each cylinder ‘giving up’ (being so lean as to cease supporting combustion) at different times during the leaning process. If there are imbalances in the fuel/air ratios being delivered to each cylinder, each cylinder will put out different power at the same place on the ‘lean curve’ and sooner or later one of the 4 or 6 cylinders will stop delivering power completely during the leaning process, and the engine will feel ‘rough’. The ‘roughness’ is actually vibration due to the imbalance caused by one or more cylinders not contributing any power.
Now the hilarious bit is that it’s possible that the point at which that ‘roughness’ occurs is when all the pistons are over on the lean side of peak and, further, that all the pistons are still on the lean side of peak when the mixture is enriched to remove the ‘roughness’. (Although that would be unusual, given the design of standard carby’d piston aero engines. That is why the folks with the real experience advocate the application of some carby heat to even up the fuel/air ratios being delivered to each cylinder.) Where each cylinder happens to be on the lean curve when ‘smoothness’ is restored is anyone’s guess.
Nonetheless, the pilot will be able to look yr right in the eye and say: “I always run it rich of peak”.
Hi No Hoper
If I’m a knob for preferring to heed Mr Atkinson’s advice, roll me in lead oxybromide and call me ‘Nobby’!
The best engine troubleshooting tool is an engine monitor and knowing how to interpret what it’s displaying. If I want to know what an engine monitor is telling me, I’ll listen to and learn from Mr Atkinson and his colleagues, thanks very much. After all, it’s no skin off your or yr right’s nose. If Mr Atkinson and his colleagues are selling snake oil, some lucky engineer will make money out of fixing my prematurely failed engine.
(BTW: I should declare that have no direct or indirect pecuniary interest in any brand engine monitor, any brand engine, any brand spark plug, the Advanced Pilot Seminars or any other course. My main interest is in staying alive, which always depends on me treating my engine with tender loving care.)
Last edited by Creampuff; 9th Apr 2014 at 08:50.
Reason: Had to stick 'in' in!