that could possibly be it, i'm not positive on it though, i believe those 4 screws you are playing with are your mixture screws though, not the main idle adjustment, those are more for fine tuning per say.... the main idle adjustment, on most carbs, i dont specifically know your carb, is a screw that is generally under the throttle linkage, and will pull the linkage back when you tighten it, and let off on it when you loosen it, pretty basic eh? but first you're going to have to retune your mixture screws before setting that idle, on a standard application you ussually bottom the screws and then back them out about 1 1/2-2 3/4 turns... once you get that all set, you're going to need to drive it a little bit to tell if its running rich or lean.... if it smells a little gassy, then you've richened it too much.... pull a plug when you're done driving around and see if the tip of the plug looks like its been burning dry or if its getting over saturated, should look like its been getting just a little wet... again you should check float levels in your carb also to make sure its setup just right, you should be able to open up the sight holes and see the fuel level just a little bit below the hole