There is no set limit. Its all personal. Some people choose to go very low carb, (less than 30g a day) some find 100-120g of carbs per day works for them, some people settle somewhere in the middle.
The best way to discover your limit is to test. If your DSN wont give you a meter or strips I would recommend buying one. Its the best guide to how your body copes with sugar and carbs. I bought mine from ebay, but its also on amazon, it has the cheapest strips and is the SD Codefree moniter.