I don't think it's sludge in the gas tank. More likely a problem with ignition. Get yourself a tube of dielectric compound (also known as "tune-up grease". Put a little dab on the contact of your ignition coil's terminal. It's also great for battery terminals, works as well as petroleum - for keeping them clean of corrosion. I would replace the wires and check the plugs (hell, might as well get a fresh set of NGK's while you're at it). I don't know about the '92 model, but if it doesn't have "distributorless" ignition, I would suggest replacing the cap and rotor. That would be where I'd start. When you're trying to self-diagnose a problem, always start with the simple stuff. You're not going to be able to see the inside of the gas tank without ripping and tearing for hours.