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.

A Dremmel tool with small abrasive cutoff wheels was used to cut along the line formed by the weld. I left a little metal uncut, then grabbed the small segment with a pair of forceps and fatigued the metal until the section was free. Then I pushed down the flapper with a screwdriver and pulled the section out. This was repeated for the other two sections, then the side of the cutoff wheel was used to smooth the cut. Work slowly and use a trouble light so you can keep tabs on where the cut is going. The photo shows what's left of the flapper, and remnants of the cutoff wheels used to make the cut. It took three wheels to get all the way around.

And in case you were wondering what the flapper looks like, here's a shot from underneath, showing the spring mechanism. It's very well built, and even though some claim to have removed it with pliers, I wonder how round the filler neck is after the procedure.

When you're through grinding and hacking, take the tank back off the bike and flush it out with water again. You might want to use hot water to help with evaporation drying, but if you leave the tank in a warm room overnight it should be dry to reinstall the next day. Remount the petcocks and reinstall the tank, making sure the drain and vent lines go to the proper stand pipes under the tank.

To celebrate, go out and fill up your tank with go juice, and wonder why you waited so long to make your life better.