What's up just bought my first yamaha. It's a 2000 R6 with 25k on it. A little history of the bike I got it from a friend who bought it with a cracked case due to a chain snaping. He had the case welded up and the engine was gone thru all the bearings were replaced as well as seals. Don't think they did the rings tho and am unsure if the valves where checked. Any who it has a yoshi slip on and seems to run pretty lean off idle. I took the carbs off last night and the slow jet is a 35 (stock for california) I order 40s for it and the mains were 144 which I don't quit understand becasue stock is supose to be 148 for ca. and 152 for everywhere else so I order 152s for it as well. I cleaned the carbs out and now it runs pretty good and strong but it miss fires on idle and low rpms under load once it hits about 3k it takes off like a bat out of hell. Any ideas? I'm going to pull the carbs off again tonight and check the plugs and coils. Also going to try and find a compression tester tomorrow to do a compression test. Should I check the valves while I'm at it?
http://i39.photobucket.com/albums/e192/weasel82185/da75cb23.jpg

Sounds like a dirty carb maybe.... hard to tell without being with the bike and troubleshooting it.

a friend of mine had the same problem with his honda f4 and it turned out to be the coils. id check into that before i would go messing with the valves. but i compression test cant hurt