I'm not sure what you mean by "magneto drive gear" The mag rotor, (magnet) is attached to the end of the crankshaft. There is no gear involved. On the right side of the engine is the primary gears. The small one is attached to the crankshaft and it meshes with the larger one that via the clutch and a countershaft drives the sprocket on the left side. Replacing the gears on the left does not effect the location (index) of the magneto rotor so ignition timing is uneffected by gear location. Did you have the magneto coil off the engine? It can be installed backwards but the magneto cover will not go back on if you did. Can you post a photo to show which gears you replaced? Also we're assuming your engine is a two stroke.
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Last edited by 2door; 08-07-2009 at 02:05 PM.