The Answer to your question RJ19LM spark plug set at 20 thousand of an inch.
My Ariens manual for the Mod. HM80 tecumseh engine, made in 1980 says to use the champion RJ-17LM, and gap is .030
Tecumseh website, "All spark plugs air gap is .030."
According to my owners manuel the spark plug gap is 30
Tecumseh Part #611049 - Champion Spark Plug #RCJ8Y
My book for my John Deere snowblower , which has a 5 horsepower Tecumseh engine , shows to use the Champion RJ17LM spark plug
I have used a Champion RJ19LM or J19LM, both work fine.
Set the spark plug gap to .030"(.762mm).
The plug gap for a 5.5 hp Tecumseh is .030 in.
Actually, there are a few different possibilities depending on the exact model of your Tecumseh. Here are the most common models that were equipped with 8.0 HP engines, and the corresponding correct spark plug (note, part #s are for NGK brand plugs. If you go to an auto parts store or power equipment supplier, they will most likely be able to interchange the part # if they don't carry NGK). H80, HM80: BR4LM HH80, HMSK80, TVM195, TVXL195, VH80: BR6S Snow King 4-Stroke engines HMSK80: BR2LM
.030
.30
Chanpion RJ19LM
Champion RN4C