Engine "hiccups" at Lean of Peak (LOP) with Garmin G3X's Lean Assist

[Neal]

I have a CubCrafters Carbon Cub FX-3 with a Lycoming IO-360 modified by CubCrafters as a 363i. I've had an interesting experience at times where there is a hard thud in the engine, certainly gets your attention, but it is like a hiccup in the engine while running such as yesterday at 20/20. It happened in the past, several times yesterday, I go full rich and it goes away. There was mentioned by someone either on this site or the CC forums about the engine possibly being too lean and that is now my belief as well.

Yesterday I had to use Lean Assist several times as the first time the numbers looked too low when all four cylinders went blue. I then did lean assist again this time doing it much slower and things looked normal. You can definitely feel the engine retarding as it leans and decreases power in this process. Was a little eye opening and very apparent yesterday.

I'm going to start looking at doing LOP by the numbers instead of the blue bars and maybe settle more towards 30 LOP instead of whatever the blue bars give me. Savvy's guidance we all seem to know is around 50 LOP but that may not apply to all engines.

Fuel flow was around 5.8 at 20/20, full rich was twice that.

Moral of this story is the Garmin G3X Lean Assist feature may not be the correct target.

 

[Schwbo]

I always go by the numbers. It’s a much better way. Also, I go straight to the numbers in one go and don’t go into the red box.

I normally fly 25/25 and lean to 8-8.5 gal/H. Gives me speed and good endurance.

 

[Neal]

Thanks @Schwbo - what is your target for LOP such as 30 or 50 degrees?

 

[Schwbo]

I don’t look at egt as the primary measurement, I go by CHT. I try to have the cht at 350-380 range and egt below 1400. I lean in one go until I feel that I start to lose power and then can work around that point. If I’m looking for speed I’ll push fuel flow to 9-9.5 gal/h and if I want more economical setting I’ll go down to 8. You can also fly 23/23 at 6.8 gal/h.