i dont know about the 250 grips but for the yami it would be way hard to do that, why do you want your old grips anwyways if your switching them? i just took a blade to them came right off used alcohol to remove all the junk, wasent much then put my new grips is soapy watter for like 5 min put a little soapy watter on the bars and they slid on just like when when you do a slut....(can i say that) took a blow dryer to them to dry them up left them over night next day dry and ready for use best and easy way 10-15 min tops!