5-5gram rollers, or 7gram Dr. Pulley sliders.
OEM carb is 17mm, and you can get a replacement 20mm on Fleabay for like 30 bucks.
My guess is your cylinder is wearing out. Big Bore Kits are 50 bucks, and work great with the 20mm carb.
Also a Malossi Red control spring is the best 10 bucks you can spend.
If you can run a compression test it will tell what shape your cylinder is in. It should read around 140, and if it is 120 or less... replace it. New kits will read between 140, and 160ish