I think the filter is no brainer but the plugs are kinda iffy (to me). I usually just change plugs and all the filters when I get a new bike car but that's when plugs are $1.50/ea and air filters are $8 haha. After looking for 2 days it looks like cheapest plugs I can find (NGK's) are $6/ea and cheapest air filter is $30 for stock, $50 for K&N. So $55 or so for stock and $75 or so for stock plugs and K&N upgrade.

Also, going by the coloring on my plugs (doesn't look lean already does it?), would a K&N lean it out too much or should I stick to stock? I'm NOT rejetting the carbs because I HATE messing with carbs and they look like a nightmare on this bike (99 CBR 600F4). Only mods are a Two Bros. slipon. I suck at judging plug color unless its really obvious like caked in oil/gas or really white... I forget what that brownish color means -- just old?

The air filter looks like it could be the original... and the bike has 41,000 miles! I pinched out pieces of leaves and bugs out of the bottom of the air box... it was piled up.

 

That looks rich as a mother to me. Id say change em and you should be alright with a k&n. Id get a bmc personally i have a k&n (bought it used) but the bmc is top of the line.

 

Well the only time the bike runs less than perfect is WOT at 10-13K rpm and it slightly surges. Just enough so I can only tell if I'm on a WOT run just to test it. Didn't notice it for the first 300 miles of riding even. Maybe the K&N would lean it out just a hair and take care of that. Found the K&N for $61 at my Advance Auto Parts, and they carry the NGK's for $6/ea. They order them and have them next day. I know i can get the K&N for $50 or so online but the $11 is worth the overnight and knowing I'll get it soon instead of some unknown eBay seller. And that way I can leave my bike half apart and not have to put the plugs and filter back in just to ride for a few days then take it back apart.

 

I'd replace those plugs, they indicate that your bike is running a little rich.

 

i say run bmc lol

 

could also be running rich because of the clogged air filter so just replacing both of those might fix it

 

My bike ran a little rich with the dirty stock filter that was on the bike when i bought it. I replaced it with a k&n filter and it felt 10000 times better, but I had an annoying hole in the power about 5-6k. I just switched to a stock oem filter today, and the midrange is MUCH smoother. I might have lost an hp or two up top, but its so much smoother this way. The powerband feels more linear.

I know on twobrothers website, they say use the stock filter and jetting for best results, but whatever you decide to do will deffinatly be better then that dirty filter! I would repalce the plugs too. Getting them out is half the battle!