Blade 500 3D - Rudder Servo Twitch

[RegularCat]

First I'd like to say thanks to the members of this forum. I can't count the number of times I've come to this forum to get information about my old school Blade 500. I've searched and I wasn't able to find this particular issue already referenced in this forum.

Long story short, I recently replaced the stock gyro with a brand new JR370 3D, and at the same time I replaced the tail servo with a new Spektrum SPMSH410 Standard digital servo. I figured it'd be a relatively cheap upgrade to the original setup. Tail is already ground to the motor mount (thanks forum members!), and the gyro settings are the standard ones in the instructions.

My issue is that when I give the throttle quick increases I can clearly see the rudder servo twitch and cause the heli to spin counter clockwise. If I slowly spool it up the servo doesn't twitch...but any quick(ish) increase causes the rudder servo to twitch...but only in the one direction. Just to experiment I've tested it with the gain, expo, D/R and servo reversing function all adjusted and no matter what...I get the servo twitch. It's not a huge twitch but it's enough to spin the heli. This happens in both HH and Rate Mode. In both modes the servo functions correctly except for the on-throttle twitch.

With the motor off...I can move all of the servos rapidly and I don't get any sense of a brownout. It seems though, that the rapid draw of the motor is causing a split second dip in power to my new servo/gyro setup. My new rudder servo is the only new, digital servo on the heli. The other servos are the stock ones.

Any help diagnosing this issue would be greatly appreciated.

Thanks!
RC