Not sure what a Carpenter stage 3 motor is I have the 240 kit in mine thought about changing to the 1.4kw starter motor in 2015. But with larger cables and good battery and the fact that I've learned to be a old lazy arse mine spins over just fine. I'm not telling not to go with the larger motor I'm just suggesting you look at your cables at least the ground cable but I'd do both. The check out the selinoid plunger contacts if your having sparratic issues even cleaning and filing them will help. What year bike do you have?