Gotta put my 2 cents in. I had both my yz125x and yz250x heads modified by RK TEK

I put the 125’s on and went for a ride. Little while later I went out on a longer ride.
Definitely a big loss of power everywhere.
Now I know why all the so called enduro riders like all these heads. I makes them run smoother, takes off low and midrange power making you think you got more overall power. But it also took off so much top end power I could hardly pull a wheelie in 3rd.
Flat unresponsive power.
I already took it off and I’m not even going to waste my time putting one on the yz250x.
In just a couple minutes almost fried the engine, note the odd lines in the cylinder.
Probably why I could never get my beta 125 to run worth a shit with one either.
Never again!