Evo Spark Plugs and Air Filter Service

Before removing Evo spark plugs, it is always a good idea to use compressed air to blow away any dirt or debris that may be in the immediate area of the spark plugs. It is vitally important that nothing falls into the Evo spark plug openings in the front and rear heads. Pay attention to the way the spark plugs feel as they are unthreaded from the heads.

Once removed, the Evo spark plug ends should be examined to help verify or determine how the engine is running. Every Harley Davidson service manual has a spark plug identification chart so an owner can compare spark plugs to images of different conditions.

Always check the Evo spark plug gap prior to installation. Never trust that a new spark plug is correctly gapped. It is also good practice to add a dab of never seize to spark plug threads prior to installation. Always start threading spark plugs in by hand. If you can not easily thread a new plug into the head by hand; stop immediately. Determine what the issue may be. Do not damage the threads in the head by trying to force the spark plug in deeper. Tighten Evo spark plugs 18 to 22 ft lbs. It is also good practice to add a dab of dielectric grease to each end of the Evo spark plug wires.

Air filter and air cleaner assembly maintenance is another important service point. An air filter that can no longer be sufficiently cleaned should be replaced. If a filter is washable, it should be cleaned in a bucket of warm soapy water, then air dried prior to installation. The air box should also be thoroughly cleaned. Lubricate moving carburetor parts and throttle cables. Inspect throttle cable adjustment. Verify that full open throttle can be achieved and that the throttle snaps back to zero position.

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