Fuji A and SAS,
It is my strongly held view that 'fancy pants digital' technology should be mandated for all 'big bore' IO engines, along with appropriate instruction on it's use and the internal workings of piston engines.
But that won't happen.
That being the case I would recommend the following.
On climb;
Set MCP on takeoff and do NOT touch it again on climb until 3000' or leveling off. By that I mean follow the POH. IO470/520/550s for instance have MCP of 'full throttle/2700RPM/full rich(at sea level). Setting 25/25 at 1000' after takeoff is bad for your engine and reduces performance at the worst possible time....Some parts of the EU mandate prop governers be set at 2500 RPM for noise pollution reasons. That is the only reason an IO 520/550 has that limitation.
If climbing significantly higher than 3000' lean to about 120 degrees ROP passing 3000' and then give the mixture about a 1/3 twist leaner every 1000' or so after that....keeping an eye on your CHT/EGT of course...enrichen if you get roughness until it's smooth again...watch the EGT each time you twist...sooner or later...probably around 9000' you will see it
decrease which means you are LOP...probably a typical engine won't do that AND run smoothly, so enrichen a bit and then leave it...it's about as good as you'll get. Be aware that once you are up around 7000' your available % pwr is getting well below 75% so you really cannot hurt the engine.
High speed cruise;
Obtain from the POH the MP/RPM combination that they suggest equates to 75% power...but do not lean further than 80F ROP EGT.
Long range cruise;
Obtain from the POH the MP/RPM combination that they suggest equates to 65% pwr and lean the mixture to peak EGT...or as close as you can get while maintaining smooth running...might be around 25F ROP.
The oldest aeroplane (aside from various vintage biplanes etc) I have flown is a 1956 C180 that belongs to a mate and now resides in the UK, G-BTSM...once upon a time it was P2 (PNG registered). It has an EGT gauge...surely aeroplanes not fitted with at least an EGT gauge are a rare thing these days?
It, of course, is not IO but merely O so all bets are essentially off. The fuel air ratios in most non injected engines are so random that all you can do is lean to rough running and enrichen for smooth running...but the same 65-75% power considerations should be observed imho.
In the old days when I was flying IO and TSIO twins for a living we would not lean them below, from memory, 60-80F ROP for the IO engines and about 100F ROP for the TSIO engines...and we had few problems with the IO engines...TSIO engines tend to eat cylinders almost no matter what you do.
I also lean brutally on the ground as soon as it settles down in idle after starting on my aeroplane...it completely stops 'morning sickness' (fouled plugs). But you must develope a habit of going 'Mixture, pitch and power' as you begin each takeoff lest you forget and try to takeoff with a lean mixture. Another way to avoid that very damaging possibility is to lean
so brutally on taxi that it dies when you try and increase throttle on that takeoff without going full rich. That is called a lean mixture cutout...too much air/not enough fuel.
