Yes sir it is! I always used to hit it on my dads dirtbike accidentally
-Brett-
So, maybe pops might have done some flat tracking years ago, cause that is what those compression release were made for, best as I can remember.
If you flat tracked & had a two plug hole head on your enging, it had a compression release in that extra hole.
When you backed off the throttle going into a corner & pull the lever, you could feel a drag on the engine slowing you down just a bit.
Years later though & thinking about the design, wonder how much raw air being sucked back into the cylinder when its opened. Because its not a check valve, its open when the piston going up & then when its going down & sucking in air.
I had a 74 Yamaha 360MX set up flat track I used. That was the meanest bike I ever throwed a leg across in all my life, specially when I first got it & in the MX set up. New low flat track pipe tamed it down just a bit, but that lite switch coming out of a corner was still there.
Neil