The float type carburetor on my Briggs and Stratton engine leaks gas out of the throat. I replaced the needle valve and seat but apparently that wasn't the problem because it leaks just as bad as before. I notice when the engine is not running I can shut off the valve between the gas tank and the engine and drain the carb bowl of gas, then turn the valve back on and allow the bowl to refill and it won't leak at all, until I start trying to start the engine. Then it just starts leaking again. What else could be causing it to leak like this?

So, long story short, a neighbor is loaning me her tiller that she loaned to another neighbor. When she got it back from the other neighbor "something had fallen on top of the tiller and cracked the gas tank". The gas tank is destroyed - several hairline cracks and it leaks gas all over the place. The gas cap is broken, too. I want to use this tiller tomorrow morning. If I find another small engine gas tank, can I just replace the broken tank with the new tank? I'm sure it won't be a match but if I can find a way to attach it securely, the fuel lines are the same size, and it doesn't leak - would it still be safe to do? The tiller is a Craftsman with a 5.5 HP Briggs and Stratton. Thanks for your advice and suggestions!