Yo Kenny, welcome to the club!
For the benefit of others who has not been following this thread, I am still living with the abovementioned problems.
Here's my thoughts:
1. Kenny, perhaps u might want to re-adjust your lean air/fuel ratio via the screw located beside the engine body. It might be that your mixture was adjusted to compensate for the faulty valve and so tho it might work previously, it is actually low on air and thus your new valve makes it even leaner to the extent that it stalls. Just a layman's thot on this.
2. You might want to try the new valve on my car and see if the same thing happens. Might yield more leads that way.
Awaiting good news from u, cheers!