It has the original 1.5L motor carbureted. Ever since I got the thing it will not stay running when cold unless I keep my foot on the gas. As soon as I let go, it dies. Once the temp gauge begins to rise it will idle fine, albeit high around 1500rpms. Even once warm, the idle always stays up around 1500-2000. Could it be a vac leak?
Thank you!

 

How cold are we talking about? It could be many things.

Have you checked to see if the electric choke is working? the choke plate should be closed when it's cold, so you'd be running rich and have a high idle until it's warmed up.

To check for a vacuum leak, get a can of carb cleaner and spray in little spurts around vacuum seals and gaskets. If the idle surges up, then you know you have a vacuum leak.

Did you just rebuild the carb? Maybe the idle mixture adjustment screws are out of wack. There's also an idle stop screw. May it's turned far enough in, that it doesn't let the throttle completely close.