I'm quite sure I should not do this but the regulator you are using is here:
http://store.norgren.com/us/en/detai...ure-regulators

and this has nothing to do with automotive application....
under the technical details it states you have to have a positive line pressure up to 20 bar and then the regulator will relieve.

My opition is you should just keep the standard amal valve instead of this