Tempest currently manufactures only 18mm spark plugs.

Please refer to the Tempest application chart. There are several things you will need to know as most engines have several different spark plugs approved.

1. You will need to know your harness B-nut size. This is the nut that screws onto the spark plug. It will be either a 5/8-24” or ¾-20 thread. Be aware that a 5/8-24 utilizes a 3/4” wrench and a ¾-20 utilizes a 7/8” wrench.
2. Long reach v. short reach will be determined by the specific engine.
3. Heat rating is indicated by the numeric value of the spark plug part number. The lower the numeric value the colder the heat rating. Best practice is to use the same heat rated plug you have removed.
4. Massive electrode or fine wire is a personal choice. Massive plugs will generally operate 400-500 hours. Fine wires can last 1500 hours. This choice is usually determined by number of annual hours flown and the size and performance of the specific engine.

Typically Tempest spark plug resistors will stay between 1000 and 1500 Ohms throughout their life. Tempest specifies that the plug resistor should never be below 500 Ohms or above 5000 Ohms. We offer a lifetime guarantee on our fired-in resistor.

First, the firing end of the plug must be cleaned of lead, carbon and oil. Once cleaned you can use the Tempest AT5K® or a multi-meter. If using an AT5K please see the tool section of our website. If using a multi-meter place one lead on the center electrode and the second lead on the contact point inside the spark plug terminal well. Be sure that your multi-meter is set to the correct setting.

Please visit the Technical Data portion of our website to find our articles on best cleaning practices.

Indicated by hard ash-type deposits, lead fouling can be caused by poor fuel vaporization due to cold operating temperatures or high-lead content in the fuel (misdistribution of tetraethyl lead). Lightly fouled plugs can be cleaned, re-gapped, tested and reinstalled using a new copper mounting gasket. Severely fouled plugs should be replaced with new Tempest® spark plugs.

Carbon fouling is indicated by dry, fluffy, sooty deposits. The plug is operating too cold to burn off combustion deposits. This may be fuel related or ignition related. Fuel related causes include rich fuel mixture, faulty carburetor adjustment, excessive idling or improper idle mixture. Ignition causes could be related to a worn spark plug ignition lead, improper magneto timing or running too cold of a spark plug.

Oil fouling is indicated by oily, wet deposits and frequent misfires. Causes can include damaged pistons, worn or broken piston rings, worn valve guides, sticking valves, faulty ignition supply or an engine during break-in period.

Yes, you should rotate your spark plugs every 100 hours. This will help even out electrode wear caused by constant polarity and capacitance after-fire. Place them in a Tempest spark plug tray (P/N T240) and follow the rotation guide supplied on every Tempest spark plug box.