Tecumseh model numbers are either stamped into the starter shroud or into a nameplate or tag that is bolted to through a crankcase bolt. There are three groups of numbers that give information about the engine. The first group of numbers will be the model number, followed by the specification number, and the last group of numbers are the serial number.
EXAMPLE:

The parts lists are broken down by Spec Numbers in this database.
Craftsman  Model Numbers should be entered with a period after the 143.
EXAMPLE:
143.001300