I just purchased a 1985 Suzuki gs300l. When I put gas in the tank it immediately started pouring out the drain tube that is connected to the air box. What is wrong and how can I fix it?
After they've been sitting for a extended amount of time, the floats in the carburetors tend to stick or if the tank isn't cleaned properly before filling it'll for the first time after a long off season it could allow some debris to get into one of the jets causing it to not take fuel (become clogged).
In turn, causing the fuel to backup and fill up the air-box. If this is the case the carburetor will have to removed, disassembled and cleaned, replacing all the gaskets as you go. When you put the bike back together you might want to think of investing in an inline fuel filter to prevent this issue from reoccurring.
If it is not losing fuel from the carburetor then there are rubber seals inside the gas tank that spend their entire lives covered in fuel. Over time these seals will shrink and crack and dry out. Especially if the tank is ran low a lot and if it sits for an extended period of time without any fuel in it. The fuel keeps the rubber lubricated. They sell rebuild kits for the tanks and also for the carburetors. You should be looking into getting yourself one of these kits.
I've tried looking for a link but couldn't find anything that I felt worthy enough to give. Google is your best friend on finding these parts. Best of luck.