I have a YS 70 that is loading up at lower throttle. If it were a 63S, I would turn in the regulator and readjust top and bottom. What am I supposed to do with a 70 ? ... other than putting a 63S regulator on it. Is the regulator worn out ? Statically, it seals perfectly when there is no pressure on the diaphragm and 8 psi on the fuel. Statically, the one-way valve seals the tank pressure perfectly for hours.

Your low speed needle is set too rich. It has nothing to do with the regulator.
That needle is in the center of the throttle barrel opposite the throttle arm side and counter-clockwise is leaner.

Turn it in 1/6 of a turn leaner until it dies when you punch the throttle after a 20 second idle.
Then turn it 1/8 richer and that should be good. Get this set properly and your whole throttle response will be much improved.

My low speed needle was lean to the point of popping. That wasn't it. Put a new regulator on today and all is well. I guess they do wear out. Actually richened up the low speed a 1/4 turn. The old S regulator could be renewed with a $5 nipple. The new regulator is $60.

You can buy the regulator valve and diaphragm for about $12 shipped from central.

Not for the new regulator on the YS 70 and 115.

Yes you can. Look at the parts listing. It's not in the exploded diagram.

66 YS5330 Regulator Body A 1 In assembly YS6335 - $59.95

I see the confusion. What they call the "valve" is just the black plastic disc plunger. The actual valve is in regulator body A only available in assembly for $59.95.

67 YS5340 Diaphram 1 $3.50
68 YS5343 Regulator Valve 1 $3.95
69 YS5345 Regulator Valve O Ring 1 $3.50

This would be all you need to re-build the regulator. You never had to replace the body of the 63s regulator, nor do you on this one.

Does the silicone rubber flap come with the black plastic disc plunger in YS 5343 ? Sort of like YS 5040 comes with the silicone rubber nipple ?