My kids 98 powder special 600 seems to be boggy on the bottom end. It takes awhile to react and does not have low end power but it still has top end speed. I have changed the belt. Checked the clutches. Put new plugs in. Tried high octane gas. I have also checked the compression and it has great crompression. It feels like clutching but I don't think it is. I suspect it may be a sensor because the problem just showed up. Any ideas?