Carby LOP
Here is how I get my carburetor O-360 to run lean of peak at low level.
1. Set 23 MAP 2300 RPM or thereabouts
2. Apply full carby heat (there is no useable partial setting on my plane)
3. Pull out the mixture control about 75 mm and wait for EGT to stabilise
4. Pull out mixture control until all cylinders are LOP. This takes miniscule adjustments
5. When all cylinders are LOP, push the throttle to full open.
6. Make miniscule mixture and RPM adjustments till lean "stumble" disappears (if present)
Given that I seldom fly very high this can result in the following:
27 - 28" MAP, 2300 - 2400 RPM, fuel flow around 28 - 30 LPH and cylinder head temperatures in the low 300's. Once upon a time I considered CHT of 350 good. LOP way improves this.
This gives me a cruise speed equivalent to a "normal" setting of 23 MAP 2400 RPM and 34 LPH so I am saving around 4 litres per hour or more with no trade off in speed. 4 litres is nearly 10 bucks. About $1000 per annum if I do 100 hours between annual inspections. This goes a long way towards the cost of an annual!
For this to happen I needed an engine analyzer and the confidence gained from an Advanced Pilot Course.
Does the POH allow this? Good question, my POH refers engine operations directly the the Lycoming engine book and these settings do not seem to be prohibited but it is a difficult book to read. Truth be known I don't really care, this is not a charter aircraft and 99% of the time its just me, or me and Mrs Bob on board.