Carb Deposits

My ST70 has been sitting idle in the garage for a few weeks, previously it had run ok, but now wont start. I checked for a spark and that's ok, checked for sufficient fuel and that's ok too. Pulled the carb apart and found a kind of calcium type build up in the float chamber and on the jets which wasn't present before. Could this possibly have come from the unleaded fuel I have put in it? When I first acquired it and stripped the carb these deposits weren't present. I am baffled, any ideas please guys?

Yep, modern fuel does not have a very long shelf life due to all the additives so it would be best to drain the carb If you don't intend to use the bike for a while.

Thanks.

Assuming that our bikes are 40 odd years old and were designed to run on leaded fuel should I be using an additive?

No.
They are designed to run on unleaded fuel only.

Thanks Waynus