99 YZ 250 Tuning Help

[John In NC]

I have a 99 YZ 250 that fouls plugs rather quickly. It also is a bit sluggish under 1/2 throttle, sort of like it needs to clear itself, misses, sputters and once its ready-goes like a bat. The previous owner said it will foul a plug now and then and said he uses NGK BR7ES instead of BR8EG (stock) The hotter BR7ES will last several rides. The BR8EG will maybe last one. Though it runs about the same with either plug. That is until it won't run. The carb info is PJ #50, MJ #172, Needle on second clip (all stock settings). The air screw is at 2.75 turns. Air filter is clean. The reed valves are fine. The bike also starts real easy and only needs the choke for 10-20 seconds. My thoughts are to reduce the PJ first. My real question is to what size? I live at about sea-level.

Part two is what is a good air filter supplier who also sells carb jets. I plan on having a second filter on hand.