The only way for the disc to seal is to run VERY close to the carb body. The oil film makes the final seal and of course lubricates the assembly. Without a good seal the fuel charge leaks buy and is not transferred /held in place. On my 53, I thought .001 would be a good number.... Wrong! then I tried .0005 using shim stock as a gauge....Wrong again The disc has to basically rub (very lightly) on the carb housing.

Kind of a similar thing is how the piston skirt of a 2C engine "seals" the cylinder to piston so on the down stroke there is enough"compression" to force fuel charge into the cylinder. As a former powersports mechanic we had several small bikes that had great compression above the piston (100+ psi) but ran like crap even if we did get them started. Turned out the cylinder was scored so not a good seal, no fuel transfer.

Ken