Not sure about your exact issue, but has anyone checked the fuel tank vent is clear and the hose has a loop up so water cannot get in the fuel that way. Fuel filter replaced? Fuel sample, in a clear jar and let it sit overnight...look for water at the bottom. Changing to electronic ignition was one of my best mods to my '90. I installed a Pertronix kit, about $100. Sure hope you get it figured out, and let us know what fixed it!