MG T-ABC

I assume these are pre-set? If not, how would you set up the spring length?

I'm not familiar with that particular valve but sometimes there's a nut on the back of the valve which can be turned to compress the spring and therefore adjust the opening pressure. Without that I'd say shimming the spring would be the only way to increase, and changing the spring to lower. I know there are a few guys on the email list who have set these up so if no one here has the answer then you might try there.