I should mention this 'cause the grips on the HT throttles can be a ***** - particularly if ya wanna use a nice set of bicycle grips.
It's simple enough, get say a big coffee can or w/e and fill it with hot
soapy water, throw in the china twist grip (minus kill switch ofc) and the bike grip you want to put on it and let them soak fer a few. If you used water hot enough to be not quite simmering - by the time the water cools enough that you can deal with it comfortably you can usually work the stock grip off quite easily.
The new bicycle grip is softer to begin with than the rock hard POS that came with the kit (why we're gittin' rid of it obv), now that it's been in the bucket this whole time it outa stretch over the plastic tube for the throttle with not much effort. To do this I do suggest using the end of the handlebar in the plastic tube (but without the cable and kill switch) because it's kinda easy to crush it otherwise, particularly if it's still hot.
If it starts getting really difficult, just get some more hot, soapy water and let it soak while you smoke a cigarette and chill - when you get back it outa be ready for you too
Stock Schwinn grips;
If anyone has a better way - I'm beggin' ya for it lol