Power reduction stumble?

[LouFly]

Chasing a minor nit: Consistent very brief power stumble when reducing MP from about 20" to about 10" (such as at a 180 deg downwind position in landing pattern). Just a second or two then smooths out, too quick to see anything on engine monitor
Rich or lean, doesn't seem to matter

IO320B1A 1900 hr RV6A vertical induction

• Recently replaced intake gaskets, induction hoses
• Spark plugs are clean
• Valves look great
• Mags in good shape
• Run mostly avgas, use mogas for cruise when it's available
• Mine is one of those engines that "pops" during a large power reduction (as in an overhead landing approach)
• Overall since balancing injectors, replacing baffle seals and sealing air leaks the motor runs outstanding ROP and LOP with very little CHT spread

It may be that the engine runs so well now that I'm just noticing this...any tips appreciated TY!

[lr172]

To idle and off idle transition issues are typically due to incorrect idle mixture settings. This is NOT done with the red knob, but the idle mixture adjustment on the carb or servo. The pops when pulling to idle are for the same reason, though pops are usually due to overly lean idle conditions instead of rich, though they can also occur due to leaks in the exhaust flange.

Idle mixture controls to around 1000-1200 RPM, after which it has little effect.

Larry

[LouFly]

Thanks Larry. That's a good idea. We did adjust the idle on the servo to a little leaner at the last annual. I will try richening and checking the 50 RPM rise at shutdown.

Originally Posted by lr172

To idle and off idle transition issues are typically due to incorrect idle mixture settings. This is NOT done with the red knob, but the idle mixture adjustment on the carb or servo. Idle mixture controls to around 1000-1200 RPM, after which it has little effect.

Larry

[lr172]

Originally Posted by LouFly

Thanks Larry. That's a good idea. We did adjust the idle on the servo to a little leaner at the last annual. I will try richening and checking the RPM drop at shutdown.

Need to be cautious of OAT when adjusting. Cooler intake air temps require richer settings. You want a compromise where mixture is perfectly set for the mid point of temps your engine sees OR stay a bit on the rich side to be safe. Lead fouling occurs due to low combution temps, not rich mixtures, so being a bit on the rich side won't magically start lead fouling issues.

Larry

[LouFly]

Originally Posted by lr172

Need to be cautious of OAT when adjusting. Cooler intake air temps require richer settings. You want a compromise where mixture is perfectly set for the mid point of temps your engine sees OR stay a bit on the rich side to be safe. Lead fouling occurs due to low combution temps, not rich mixtures, so being a bit on the rich side won't magically start lead fouling issues.

Larry

Thanks again Larry. Fixed the issue and diving deeper into the details of my old RSA5 was a worthy and fulfilling exercise.