Make sure your carb heaters didn't become disconnected. If both are still attached to the bottom of the carbs, let them warm up for minute or two on cold days BEFORE firing the engine. Mine starts immediately with my previous long off-road pipes and the new Specialty Spares.
If you haven't adjusted the air/fuel screws, your carbs are probably set impossibly lean, guessing adding lower restriction pipes made that situation worse. If you are any where near Hagerstown, come up to my place and I'll adjust them for you.
