power brake booster

I have a big cam and had to go with a pump actually. My vac at idle is 5-8. Easy test for the check valve is just pull it from the booster then blow through it in both directions it should only go one way. If you can get a hand held vac pup hook it to the booster some how and see if there is a leak if so its the booster. Might take a while to pump it up so be patient, big volume to overcome.