I replaced the carb on my moto4 and it will only run with the choke applied with it off it will back fire some and then it will rev up really high randomly and then idle down and die. Sometimes I have to kill it for fear it’s not gonna idle down. I’ve messed with the air fuel screw quite a bit and it doesn’t seem to do anything for it.

 

Seems a bit like a cracked inlet manifold. Yams are prone to this and the most likely time for it to let go is when you have been pulling at it to get the carb off.

 

I just checked and it does not appear to be cracked. Upon further checking though I may be an idiot. I forgot to put the o-ring between the carb and the inlet manifold. Now I have to find where I put the box with o-ring lol. Thank you so much for the help though once I find the o-ring or get a new one I’ll update on if that helps.