Sudden/multipule vibration for 20 seconds then stops

Make sure the carburetor slides move up and down easily, if not clean and lubricate the center bushing. If they do not move freely it will cause an out of sync condition.

Sorry it took so long, been working lot of overtime.

Checked the slides and both slide good and sounds good. Both lower and raise to the same height.

Any other thoughts?

It only happens in cruise and more often in a descent. Tried aux fuel pump and climbing/descending without adding power and it doesn't help. Just goes away on its own after 10 15 secs or when I go down to about 4000rpm.

Thx

Maybe you are intermittently picking up some carb ice and maybe more on one carb than the other causing an out of balance condition.