If he just "touched it" then hopefully it shouldn't be too far out of whack. The best thing to do is try and tune it back in with small changes.

I would recommend starting up the engine, get it warmed up, then throttle back to 1/3 throttle or less. With the engine running, point the plane up 90 degrees...if the engine takes a while (5 or more seconds) to speed up it's a little too rich and if it stops running it's too lean (it's always better to be rich than lean). If the engine is lean turn the engine off, turn the screw in just a hair, then restart the engine and check it again. If it's too rich do the same thing, but turn the screw out instead of in.

You can also use the pinch test (pinch the fuel tubing near the fuel inlet on the carb) at low throttle to check the tuning. For either the "pitch test" or the "pinch test" the engine should speed up a little before dropping down or quitting. You eventually want to get it to the point that it speeds up after just 2-3 seconds.If it just dies immediately then it's too lean and can damage the engine. The last thing you should do after you get the airbleed screw dialed in is adjust the high speed needle.

My friend and I have the same engine and I used this process to get his engine tuned in this weekend. The airbleed screw is not something you should be afraid of.

Good luck

Dave