I have no idea what the guys problem might be.
HOWEVER, last week I bought a new 2 stroke weed whacker and filled it with gas and 40 to 1 oil. It started right up but when I tried to open the throttle past idle it would stall. I tried several time with the same result. Stall. The troubleshoot in the manual said if the gasoline was older that 1 month this could happen. I changed to new gasoline and that cured my problem. I was very surprised. I learned from this. Pete

I feel like a vacuum leak would cause it to idle higher, unless it's a really huge leak. I'd personally say it's the carburetor. Make sure you get everything set perfectly on it. Also, I would check timing to make sure that's good as well.

I’m with miker and WHIPPER; need more information.  Carburetor issues and/or a vacuum leak would be at the top of the my list though.  On the carb it could be a number of things with the simple fixes being related to air/fuel adjustments and idle speed.  Vacuum leaks could be from a number of places but start with the vacuum hose going to the windshield wipers and the carb base gaskets.

Lorena, Texas (South of Waco)

Had trouble getting decent idle on my 56  turned out to be intake manifold gaskets letting air in.

Well, that doesn't tell us much. Turn up the idle screw on the carb?

Seriously, how much rpm do you need to keep it running?

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ