If you’ve got an R bike from the ’80s or ’90s, chances are good you’ve doused yourself with gasoline more than once while fighting the flapper that lies inside the fuel filler neck. In the photo above, the flap has been removed, leaving an opening wide enough to admit even the crudest filling device (sometimes found at points south of the border and other likely adventure destinations). The procedure isn’t hard, but does require a steady hand and a little nerve. One slip, and its new tank time.
Start by draining the gas from the tank and removing it from the bike. Remove the petcocks to make it easier to get the last bits of gas out. Wash out the tank with plenty of water to remove any traces of fuel. The last thing you want is an explosion from the sparks you’ll be generating as the neck is cut off. Set the tank back on the bike so it doesn’t move around while you work on it.
I used a demolition saw with a 6″ blade to make three cuts in the filler neck that terminated at the circumferential weld about 1/3 up the neck. The cuts were spaced so that the first piece was small enough to come out the flapper hole when the flapper was pushed down. The other cuts were spaced so that each segment was less than half of the neck wide, again to ease removal. I found it helpful to use leather gloves to protect my hands, and to brace the hand holding the front of the saw against the tank. The blade was angled so as to miss the hump in the underside of the tank, and the trigger pulsed to control cutting depth. The saw had a tendency to grab as it broke through the thick initial ring of the neck, so be ready.