Carb advice

I just bought my first SV. Its a 2000 SV650Y. The previous owner put a K&N filter and Yoshimura full system. He claims to have never touched the carbs and I believe him. I am having a backfire at idle, when the engine is warm or cold. The plugs show no signs of being rich and there is no smell of richness. Overall, the bike seems to run fine, but will backfire once every 5 to 7 seconds at idle.
Logic tells me that I'm lean. (but I've been wrong before). Oh ya, also, the guy put it up for the winter and didnt drain the carbs. The tank was nearly empty. I have filled it with fresh gas (yep...I'm American) and a little carb cleaner. I'm in the process of running through that first tank. I didn't know if my problem was partially due to the carb just getting gummed up from the winter.

Can anyone offer some advice on the best thing to do? With that filter and pipe, is it a certainty that I have to re-jet the carbs? And if so, do I HAVE to mess with the needles or just change the jets?

Thanks in advance for any help that I get.

first thing i would do is make sure there balanced first then go from there.

[yorkie_chris]

With KandN and a full system then it probably should have been set up fuelling wise.

Could have an air leak, something like a split vacuum pipe, or perished inlet manifold rubber.

Quick way to check for an air leak is to spray a bit of brake cleaner near the inlet manifold rubbers, if there's a leak the engine speed will increase.