Rebuilt the carburetor on a 1983 Sierra s15. The carburetor is a Rochester varajet 2se. Reinstalled the carburetor and now it won't stay running. It will start and idle for a min or so then surge and shut off. If I try to give it gas it will shut off. It's getting gas, I've checked the fuel filter and the fuel pump. Im stumped as to what the issue could be. Any insight would be greatly appreciated.