[Capflyer]

I believe my mixture set screw has been slowly backing out most assuredly from vibration. My engine is running richer than it used to. Upon inspection there is no safety wire or anything else holding in place other than a spring the screw goes through. There is no hole in the screw head to mount safety wire. It also turns with ease especially out CCW which richens the mixture. Is this typical? What do others have on the mixture screw if anything to keep them from turning? My carb is a Marvel MA-4SPA.

 

[walkman]

None on my

MA-4-5 on O-360 A1F6D.

just a screw and spring. does not turn particularly easy, but not particularly hard either. I guess its a sort of Goldilocks level of resistance

 

[pauldan181]

I have a MA-4-5 and drilled a #60 hole in the corner of the idle mixture knob. I ran a loop of saftey wire through it and a similar hole in the throttle cable bracket loosely (no side load). It might be able to move maybe an eighth of a turn but no more.

 

[turbo]

index it and check it later to see if it is really moving.

a 'sinking' float could cause the problem too.

there is a test where you pull the mixture at idle to get a 25 to 50 rpm rise. this will test your mixture setting.

sounds like you need a new spring to keep it from moving.