Yamaha Neos starting problem

My Neos 100 2t will only start if l push the air box pipe to one side and close off the carb intake with my hand and crank it over for quite a while till it starts, it then will restart for a while then it’s back to square one, also when l get it going it will cut out after a short after a short drive and won’t restart, I’ve replaced the vacuum unit under the tank and carefully cleaned the jets in the carb. HELP!!