Finding your model number is the first step to successfully identifying your Tecumseh engine, Below is a list of possible locations aswell as some images.

• Stamped Onto The Flywheel Blower Housing (Pictured Left), Can be above Spark Plug, At the Rear Or Above the Muffler
• Sticker On Underside Of Plastic Cowlings
• A Printed Sticker with Bar-code Usually On The Flywheel Blower Housing

The model number is split into 3 differenct parts explained below

• Model-This is used to determine the most important features of the engine such as displacement & mechanical features.
• Spec-This number is used to properly identify the parts of the engine
• D.O.M-Date Of Manufacture is used to determine the assembly date

The D.O.M can be decoded as follows 

Pre 2004 models such as "8150C" 

8 - Last Digit Of Year (1978, 1988, 1998 Decade must be guessed or assumed)

150 - Day Of The Year

C - Assembly Line & Shift

Post 2004 models such as "03188BC0010"

03 - Year (2003 Onwards) 

188 - Day Of The Year

B - MFG Facility

C - Assembly Line & Shift

0010 - Individual Serial (10th Unit Built)