You have to pull the cylinders to change the reeds as they are a piston port cyl reed combo engine. Are you changing because they are broken, or to try and gain performance? If you are going aftermarket, don't waste your time as there is no gain. Set the reed stops at 10mm and leave the stockers in there.
I think they may be broken or not seating. when you get on the throttle fast sometines it just dies flat, also it backfirs often when you let off fast. ??