Fuel Servo rebuild?

[vupilot]

Since obtaining my 1975 8KCAB one thing I have not been happy with is the below 1300rpm operation of the engine. My mechanic and I adjusted the idle mixture and settled on a setting a little bit leaner but such that I still get a little rpm rise on shutdown. Cleaned servo screens and new o-rings. Checked for induction leaks, none found. I get a little lesser than a smooth purr at 1000 rpm than I'd like. It has a slight stumble or lag betwen 1000-1200 rpm when advancing the throttle, once through that it runs great from 1300rpm on. I remember from back when I instructed in 8KCAB's years ago in a 1999 & 2001 model they didn't idle as smooth as carbureted engines either, especially when hot, but this one seems slightly worse than I remember. My 2200hr engine was swapped in 2020 with a 200 hr SMOH engine and the log doesn't say where the Fuel Servo came from just "installed fuel servo" doesnt say if it was swapped over from the old engine or if it was new in 2020. There is no log entry I can find of a fuel servo overhaul. I read the fuel servo should go about the life of the engine between overhauls. An exchange unit is about $2500. Has anyone recently had their fuel servo overhauled, does it save anything over just exchanging? I think I will have my mechanic clean the injectors first but looking into options if that doesn't improve things.

 

[Skylarktc]

For what it’s worth, I have the same issue with my 2008 8KCAB. It idles horribly, especially when it’s warm. It almost sounds like a radial the way it coughs and hiccups. Drives me nuts.

 

[vupilot]

Its worth something, thanks. I recall that with the ones I previously flew so I guess what I am really trying to eliminate is the little hesitation I get coming off a 1000 rpm idle.

 

[Tangogawd]

There is nothing more beautiful to the ears than a round engine waking up first thing in the morning!

If it's been a long time since cleaning the injectors, do that. If the screens are clogged they won't aerate properly. Also, lean aggressively on the ground

 

[vupilot]

New to me airplane, appears to have sat for a couple years before I got it. Screens were clean. Leaning has no notable difference on the ground. And according to Don at Airflow Performance if your idle mixture is set correctly, it shouldn't make much difference and he advises against leaning a properly set fuel servo with the cockpit mixture on the ground unless at higher elevations then where it was set.

 

[Bob Turner]

Interesting!
I have always heard that aggressive leaning on the ground was better for the plugs. My injected engine experience is relatively light, and even after a quarter century I still hold my breath on Decathlon hot starts, but I always lean during taxi, and have noted no ill effects.