I'm sure not a Saito expert but I own a few. And like us all I'm learning something everyday I stay in this hobby.
First thing I'd do is check my tank, fuel lines, clunk for a leak or a pinch. Is fuel fresh ? Prop balanced ?
Open the low end up a 1/4 turn or so more. Then adjust the hi end to peak then backoff rich about 4 clicks or 300RPM.
Mark your hi-speed needle position with tape, etc and run and/or fly the plane. See if your hi-end needle is moving. After a very little time of you adjusting the needle valve and the way these glow engines vibrate , it's no wonder the crummy little metal retainer clips fail. About half my engines do this. And the vibration it causes is directly linked with the torque of the engine and prop turning so you almost always have a loose needle that leans out. Rarely will it vibrate loose rich. (Maybe below the equator.
Sometimes have to fly the plane to get this to happen. Seems the vibration is less while the plane is on the ground.
To fix this problem. (If that's what it turns out to be.) I either get a second retainer clip and the added clips stops it. Or I use a small band of heat shrink .