What's going on??!!

[Suzuki_Don]

I've tried pulling the #3 plug lead when idling and there is no real changing in idle.

When you pull the #3 plug lead there should be a drop in idle speed and the motor running more roughly. If there is no change or little change in idle condition when the plug lead is pulled I would suggest there is a problem with #3 cylinder. To test pull one of the other spark plug leads and see if the idle alters much. If it does then #3 cylinder is not doing as much work as the other cylinders.

If so check valve clearances, do a compression test, etc. have you checked the coil voltage, it should be around 11.6v.

If compression is low compared to the other cylinders, you need to find out why.

[KEITH KRAUSE]

As Don said, pulling the plug lead off a healthy firing #3 with good combustion would obviously effect how the bike runs. That it has little effect tells you it isn't firing well at all.
It's also very common/typical that as the engine warms up fully the firing can improve. Heat helps a poor combusting cylinder operate better. The apparent weak spark at #3 can't provide decent combustion under cold conditions inside the engine. Before it warms up you'll typically hear some missing and moderate backfiring from that cylinder. The backfiring is mainly created by raw fuel collecting on the header walls until it combusts all at once and you hear the "bang".
Unless you can see something obvious in your electrical inspection I'd suggest a compression test if you can. Even with good spark and good carburetion you'll have poor combustion if the compression is not within factory standards. If compression is OK then double check all spark related items and then focus on the carb at #3.

By the way, small amounts of oil entering the combustion area will also semi-foul the plug and cause what you're experiencing. Worn valve guide seals will allow oil to enter at different quantities depending on what position the valve was in when last turned off. The leaking will worsen as the engine becomes cold and tolerances widen. As I said, depending on valve position when last turned off, the amount of oil entering will vary but certainly effect cold combusion and as it worsens effect combusion all the time. At cold start up, especially if it's been off a longer time, that oil's just laying in there.