Exhaust leak causing backfire?
 

I have a 90' cbr600 that ad been sitting for a while, I had the carbs cleaned and synced and replaced all the plugs and the bike runs now and is rideable but its still having a few problems. When im accelerating at low rpms like around 4000 it will backfire. I noticed a hole in the exhaust where bracket right before the muffler is. I covered my my exhaust with my hand while it was running and the idle dropped but the bike kept running. Also the idle is kind of erratic ranging from 1000 to 3500. Also when starting it i have to turn the throttle a little bit while hitting the starter. Could any or all of these problems be cause by the leak in my exhaust?

A real backfire is an issue with ignition or carbs (usually) Lean "popping" is usually an air leak somewhere.

Unless your valves are bad it should isle rock solid at 1200 rpm. If you idle is set too low you may have to turn the throttle a little when starting. If the idle is set when the bike is completely warmed up I find that it will be a little too low when colder.

Some of the issues may be cause by the exhaust leak. I would also check the pipes where they enter the head and well as whether or not the carbs are seated all the way and the all the plugs for syncing the carbs are in place.

KongBastard

I bought a bike (1989 600) that had been sitting for a while, and I think that riding it has knocked all sorts of stuff loose again ;-) I noticed a rough running issue at lower rpm as well, and found a small exhaust leak where my aftermarket pipes come from 4 into two below the bike. I managed to almost eliminate the leak with some tinkering and the bike runs so much better now. I would not have thought that it could matter so much, but yes an exhaust leak was hurting my performance quite a bit.... it was almost making a backfire type of sound, but more of a popping noise while cruising in gear without too much throttle open... it is better now.