I just fitted new grips to my bike about 2 weeks ago. how I did it, was cut the old ones off (they were stuck very tightly but came off when cut quite easily) and used a small amount of dish soap to lubricate the bar. I wiped off the dish soap with a cloth, so there was only the smallest amount of residue on it. I could then push the grips on, although they didn't go on very easily I could still push them on. They slide around for a bit, but the next day I came out and they had dried on I guess - now they're stuck like glue.
Hope that helps,
Barry
1978 CB 550