This is a 2000 Quadrunner a little less than five hundred miles. It started out that you just can not get it to idle. As engine temp changed so would the idle so you changing the adjustment screw would work only till the engine would warm up or cool down. Now just running down the road when you can get it going it cuts in and out almost like it is loading up. Cleaned air cleaner,installed new plug and gone nuts trying to adjust idle.When you first start it and rev it just a bit it will blow a little black smoke out the exhust so I also checked that by pulling the plug to blow out exhust pipe. Any ideas would be greatly accepted. Thanks

 

Check the needle & seat, those 250 carbs are notorious for leaking needle & seats.