Valiant 318 problems
Sounds like the carb has developed a vacuum leak and this is why the car is running so poorly and the reason that the plugs have changed colors. I would check the base gasket at the carb before I would go any further, this can be done by spraying carb cleaner or wd-40 around the base of the carb, then if the engine smoothens out then replace the base gasket and your done. Keep us up on whats going on.
BJR Racing