u/Accomplished-Ant8887

So I’ve got a 1967 mustang with a 289. When the car reaches operating temp and is nice and warmed up it’ll crank up just fine and idle fairly good. When I crank it however it’ll rev really high but if I tap the gas it lowers down? It also doesn’t hold idle for more than a day or two after I adjust the screw, itll idle much lower the next day when I crank it and get past the high rpm part. Anyone know why? Also, the carburetor isn’t name brand. The guy I bought the car from I think just ordered a cheap one and put it on