What is the cause of poor gas mileage in a 1988 Madza B2200 truck that runs ok but has exhaust that smells rich?
See whether the truck has an EGR valve and replace it if it has
one. If you're not sure whether it has one, call AutoZone and ask
for one. If they don't have one for that truck, then it doesn't
have one. In that case, check the timing and adjust the carb.