Re: OLD NEPTUNE 500
Yes you can get carb repair kits. These motors(at least the two I have had) use chain saw carbs and you can go to google and search for chain saw carb parts, pick one of the suppliers listed (near you if possible) and give them the carb manufacturer and model number( stamped on the carb) and they can supply kits. I have bought two types of kits - one is a complete overhaul kit and the other is a diaphram-strainer gasket kit(much less expensive). The less expensive kit is really all I have ever needed. If you have a chain saw repair place near you they might obtain the kit for you.
Good Luck