Maybe jetted wrong for your motor ??? just a guess though.
Is it a new carb ??? or is it a used one that you just "put on". If used it may need a rebuild.
The more history and information you can give the better the responses you will get.
I take it there's no choke butterfly, only prime. Check the priming system.. basically pull the little hose from near the carb base and prime. if a squirt of gas comes out, clean the orifice it plugs into... If no squirt, primer issue.
