Part of Honda's wildly popular Cub line, the C90 is an ultra-utility motorcycle. Also known as the Super Cub, it's part of the most popular line of motorcycles ever made with over 60 million Cubs sold. No machine approaches that popularity without being reliable and the Cub 90 is. It's so durable, Cub 90 owners probably won't find themselves doing much more than occasional maintenance.
The four-stroke, single overhead cam engine is the same as the CT90. In fact everything on the CT90 is the same under the Cubs bodywork. The nearly indestructible little single-cylinder engine needs the same kind of care as other little four-strokes, just less of it and less often. Like any engine, the key to keeping the Cub 90 in good technical order is lubrication. You can always come back and tune your Cub to run better, but you can't come back and lubricate it after it's damaged. So, if you're going to take advantage of the Cubs tolerance for lack of maintenance, keep up with the oil change schedule.
While reliable, the Cub 90 is small and small engines are especially sensitive to changes in their gas/air mixture. If your air cleaner goes long enough without being changed, it will restrict the airflow and cause the Cub to run poorly and probably stall or lug. It won't hurt the engine to have a dirty air cleaner; it actually protects it. So, if you don't mind running the risk of pushing it, you can wait for the Cub to tell you when to change the filter. Not until it doesn't start, but if it stalls or has a hard time starting, suspect the air cleaner. If you're in a particularly dusty area, consider a permanent, after-market air cleaner that can be washed over and over and never needs to be replaced.
Valve Tappet Adjustment
The Cub isn't a two-stroke like most small motorcycles and scooters. Four-strokes mean valves and Cubs have them: a single exhaust valve and a single intake valve. Few machines will give you an easier time with a valve adjustment. With the valves closed and the piston at top dead center, the valve lash should be 0.05 inches. With a half-milimeter feeler gauge, the tappet can be adjusted snug with the tappet lock nut.
Most Cubs were made long before electronic ignition existed on any vehicle, let alone motorcycles. They use contact breaker points. On occasion, they may need to be replaced and/or adjusted. If the contact surface of the points aren't smooth, replace the points. At maximum point opening, they newly installed points should be .3 to .4 mm.
While not as important as engine oil for longevity, make sure your other working parts are lubricated from time to time. These items may be even more important for safety. The most important parts to lubricate, other than the engine, is the drive chain and cables. Lube your break and clutch cables at the first sign of any tightness or binding. Inspect your drive chain regularly to make sure it's well-lubricated. Chain failure is improbable but on the rare occasions it happens, it can be extremely dangerous.
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