Pull the boots off the carbs and inspect the slides. Both should have the same amount of opening. If not adjust the higher one down until it matches the lower one. You also might want to check to make sure both slides open all the way simultaneously. You can do this by eyeballing the slides and adjusting the cable adjusters. Put the boots back on. Start the bike. Adjust the two idle screws together until you've got the idle the way you want it. That's how my 350 worked and believe me I had to do it a lot. If the idle is screwed up and you can't get it to idle down then you should adjust the air screws. You don't have a manual yet?Yeah me and two friends stood there and stared at those two screws. I was afraid to turn either one figuring I'd completely screw it up and I'd have to push it home. I thought that's what they were for.
The cool thing about a 4000 rpm idle is that all the cars at the stoplight know you're there!