The engine only idles at half throttle any lower it stalls,from half throttle idle to full throttle it transitions okay but will only stay running at a half throttle idle,any ideas what's wrong?thanks for any help

Who tuned the engine?
How was it tuned?
Where are the needles now?
What prop are you using?
Is it mounted in a plane or a test stand?
Are you moving the throttle with a servo or by hand?

Are your throttle stick, servo arm, and carb arm aligned about as expected?

In other words, is the carb set to idle at half stick?

Throttle alignment not servo are fine,factory settings on carb

16×8 prop

There is "NO SUCH THING AS FACTORY SETTINGS ON CARBS". Even if an engine is "factory ran before shipment, their prop, fuel, oil and air pressure are not shipped and what you are using is different and demands proper tuning.

Knowledge is power.

Very carefully close each needle note the current position and counting the exact number of revolutions.
Low =?
High =?

If they are any where close to low needle 1 1/4 high needle 1 3/4 then go ahead and reset them to where they were.

If not try tuning the engine.