backfire through the carb.

Is it possible water got in the distributor cap when you washed it? That's the first thing I'd look at. The radiator hose collapsing is a different problem. It's generally caused from the overflow being blocked.

BTW: Why did you put 100 octane in it? Is it a real high compression engine? If it's not you just wasted alot of money because the higher octane fuel is the slower it burns so if you use it in a engine that doesn't need it it actually can lessen the power output.