Same way is Shindawa T254 if Iam correct, It is a 4 stroke with oil/gas mix. It is called the Hybrid.It has reed valves and is"supercharged"
by the movment of the piston in to the crancase. When piston goes down the first 360, Intake is closed, reed valve open the preesure gets in the intake then it close the reed valve, next stroke around opens again, intake valve opens and so on so forth.
I have one of theose engines but seeams like I have no time to go around.
Regarding the 456 ...Jim, if I remember correctly if not shoot me...LOL you are right the spring behind the membrane helps to move that back.
Material is to soft and does not come back by it self. we talk about that long time ago an I try on different carbs from walbro to put a spring behind like WT 456-1 and it worked on all of them on 4 strokes engines. Now on the other hand the Zama C1Q-P8 is a direct replacement for the WT 456-1 and also this one was discontinued and not replaced by another one. This carb does not have a spring, material is stiffer and I got lucky and got quite on few of those from an old stock .
Lately I did a Saito Twin 270...with that carb,and runs real good close to 2 min / 1Oz(30ml) spins a Vess 20B 6500-6700 RPMS depending on what time a day , morning (dense air) 6700- mid day when hot 6500. But it runs real nice, if I get time to edit the video I will post it.
I try also a 7.14mm carb same thing, I went bigger venturi ....Got a more crisp throtlle resopnse close to 7000RPMS ....but the down fall will not hand start, will not transition right...once it gets over the midrange and makes it to WOT....it screams...
Did couple heli engines On glow CDI, curious to see what customer will have to say about that...

That about me lately,...real busy

Thanks
Adrian