How to Upgrade the Performance of Honda CB 350s


Honda's CB350 twin, produced in large numbers from 1968 through 1973, received considerable praise for its reliability and versatility. Used today, these diminutive 348 cc motorcycles serve as highly economical commuters and easily transform into a potent, high-performance machine. There are several options to increase your CB350's performance capabilities, whether you plan to compete in vintage road races or just want a bit more oomph on the road. Perform many of the upgrades yourself, but major engine work is best left to the specialty shops.

  • Replace the stock 16-tooth drive in the front and the 36-tooth drive rear sprockets to change the motorcycle's final gearing ratio for greater acceleration or for an increase in its top speed. For quicker acceleration from a standing stop, replace the sprockets with a 15- and a 38-tooth drive sprocket set. Alternatively, an 18- and a 30-tooth drive sprocket set will increase the motorcycle's overall speed, while reducing low-speed acceleration slightly.

  • Replace the stock 30 mm constant velocity carburetors with an aftermarket mechanical slide-operated carburetor set. CV carburetors rely on the vacuum generated by the CB350's motor to raise or lower the carburetors' throttle slides, which provides a reliable throttle response beneficial for normal street riding. However, this generates a slight lag in response when cracking the throttle open from low speeds or a standstill. The throttle slides used by mechanical carburetors open and close solely by cable, and offer an immediate response to the slide's position. Additionally, fine-tune your CB350's performance by replacing the aftermarket carburetors' fuel jets and needles with a wide variety of jet sizes, allowing you to alter the amount of fuel metered into the motor. The jet selection for a stock CB350 carburetors' set, however, is limited only to the stock jetting setup, which in turn depends on the availability of a diminishing supply of jets.

  • Install a pair of performance air filters and a free-flowing exhaust system, in conjunction with a set of aftermarket carburetors. The less-restrictive nature of a performance air filter pulls in a larger charge of air into the carburetors with every intake stroke the motor makes, where it mixes with the increased fuel stream to create a stronger combustive force to propel the motor. Once the spent air and fuel vapor releases from the motor, a free-flowing exhaust system creates power by providing a direct route for the gases to exit. As an added benefit, the next intake charges pulls into the motor quicker by the vacuum generated from the rapidly escaping exhaust gases.

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