Briggs 5 HP Flathead Spark Plugs

I know this has probably been brought up 100's of times, but what spark plug do you use in your Briggs 5hp flathead ? Heres what I'm starting out with.

I also have a Autolite 411 coming in today.
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Spark plug heat range, and how is this determined. Why do we need a hotter or colder range spark plug !?!?! This stuff has always puzzled me....I mean a spark plug is a spark plug...Right ?
Autolite Indicates the heat range with the last digit of the part number. For example , starting with part #24 . If you want a colder plug you would use a #23. If you wanted a hotter plug you would use a #25.

Here's a pic of how they change the heat range on spark plugs.

When making spark plug heat range changes, its better to err on the side of to cold a plug. Running to cold a plug can only cause it to foul out. Running to hot a spark plug can cause engine damage if not caught in time.
I've also found out that spark plugs like Champion, Autolite and Bosch the higher the number the hotter the plug. For NGK, Denso and Pulstar the higher the number the colder the plug.:confused:

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Normal Spark Plug
Correct heat range of spark plug is being used.
Appearance- Grayish-tan to white color.

Normal with Red Coating
Coloration is from the use of additives in unleaded gas.
Appearance- Pinkish red color on the insulator.

Fuel Fouled
Indicates the cylinder from which the spark plug came from is not using all the fuel supplied to it. Possible to cold of heat range on plug or too rich fuel mixture.
Appearance- Firing tip is damp with gasoline and insulator is charcoal black.

Caused by low octane fuel or over advanced timing.
Appearance- Insulator is usually cracked or chipped or broken.

Worn Out
Spark Plug used beyond its intended life.
Appearance - Center and ground electrodes are eroded , and excessively worn away.

Spark plug is operating too hot at high speeds. Replace with colder plug.
Appearance- Ceramic insulator tip appears to have a melted, glazed coating.

Carbon Foulded
Spark plug heat range is too cold and/or caused by extensive low-speed; short distance driving.
Appearance- black sooty coating on firing end.

Sustained Preignition
Check for correct application of spark plug (heat range to hot, wrong spark plug for engine, over advanced timing or lean fuel mixture.
Appearance- Melted center and ground electrodes

Ash Deposits
Caused by the use of leaded fuel , fuel additives and /or oil additives. Check for worn rings and/or valve guides
Appearance- center electrode and ground electrode and or ceramic insulator tip tan in colored deposits.

Oil Foulded
Caused by presence of oil in the combustion chamber. Worn rings, valve guides or valve seals.
Appearance - center electrode and or ceramic insulator coated black, oil substance.

Mechanical Damage
locate and remove foreign object from inside of cylinder. Check for improper spark plug reach.

Lead Fouled
Occurrence is from use of leaded fuel or additives containing lead.
Appearance- ceramic insulator tip is coated with a brownish-yellow glazed coating.
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My son has rebuilt many Briggs. He used to use the Champion J19LM plugs, however, he got a few "Duds" brand new out of the box. Since switching to NGK plugs a few years ago not one single problem. In addition, I participate on a small engine repair forum and the general concensus was that Champion were not what they used to be and are to be avoided. In fact, we use NGK in ALL of our engines. The plug for your engine is NGK B2LM.