When I ran out of fuel in my 79 XS1100, and then poured fresh gas in the tank and opened the petcocks, fuel leaked from the air filter. The cause: The floats dropped to the bottom of the fuel bowl. When the petcocks were opened and fresh fuel flowed in, one or more of the needle valves stuck, as it was trying to reenter the tube that it slides up and down in. The fix: Tap the float bowl with the kick starter lever or something similar.
When working on carbs, you will notice that the needle valve can stick like this at the bottom of its travel. It happens.
We need to be sure it is moving up and down freely. The crank vents in to the air box. Over time an oil residue coats the inside of the air box. Add some fuel to that, and it dissolves the oil residue. If there is a lot of oil residue, it means more pressure in the crank case, which is caused by compression gas going past the rings. Low compression would be a sign of this.
UK
