Compression for WR and CR

I change my piston in my WR 240 1985 single ring for a piston CR double ring and I lost some compression. If I look in my technical data of my WR 240, my compression ration is : 15.0:1 (or 220psi). This compression is 15kpa. With my new CR piston I have 11kpa (or a bit more then 150psi).

My question is: is it normal with a CR piston double ring you have lese compression then with a WR piston single ring?

Also, I have to put my throttle screw all over in if I don’t want the engine to stop on idle.

Thanks

Have you run in the new piston? are the new and old pistons identical other than the second ring and are the new gaskets the same thickness as the old?.
Idle issue sounds like your bypassing the idle circuit, you may have a blocked or too smaller pilot jet, check your reeds as well another thing to consider may be a different idle screw has been installed.

Sorry couldn't Finish last reply due to a Skype call, but if your pilot is way too big you have to increase the amount of air with the slide for an idle, does the bike start easily without choke when cold if so this indicates too rich pilot.
Did the idle issue exist before the new piston if not then run in the piston retorque the head and adjust idle.
Lower compression usually means lower vacuum which means less fuel Is syphoned through the pilot and less air is needed to maintain idle as long as vacuum picks up enough fuel to maintain the idle.