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Instructions
Remove the four bolts that hold the head sink (head) on top of the engine, then slide off the head to reveal the glow plug underneath. The glow plug will extend from the bottom of the head, allowing you to assess its current condition.
Assess the appearance of the glow plug (found in the center of the head). The plug should have a thin coat of oil on it with slight discoloration on the surrounding area of the glow plug. This condition is good during the break-in (which consists of running the engine for two fuel tanks while making adjustments), but the present condition will dictate your next move. Install the head back onto the engine and tighten the screws.
Use the screwdriver to lean out or enrich the engine after driving through a second tank of fuel. These terms refer to the proportion of fuel-to-air mixture entering the engine's combustion chamber. If your glow plug matches the previous description, tighten the high-speed needle (found protruding from the front of the engine) a quarter-turn after the second fuel tank is emptied. If the glow plug was clean (and not at all discolored), remove the head again and check its condition. It should appear as previously described in Step 2, in which case you should make mixture leaner.
Assess the appearance after the second fuel tank has emptied to determine the combustion chamber's condition. If the residue looks the same, your engine is tuned; but, if it is silver to slightly tan, or if there is very little residue, your engine is pitting -- the glow plug is being pushed up into the head by the close proximity of the rotating piston. Correct this by removing the head and installing a spacer shim, which resembles a washer, between the head and the combustion chamber. This shim will reduce the occurrence of detonation by increasing head clearance inside the chamber.
Assess the appearance of the glow plug after the second tank to determine whether the engine mixture is running too lean. This is indicated by very little residue on the glow plug itself accompanied by slight pitting. If this is the case, use the screwdriver to turn the high-speed needle a quarter-turn to enrich the mixture.
Continue to check your engine's condition after each gas tank until you achieve perfect tuning. This is indicated by an even, light-brown to deep-golden appearance across the entire combustion chamber and glow plug. Your engine is tuned and break-in is complete.