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5 Tuning Tips for Your Gas Powered Bicycle
Last Updated: 11/05/2015

Building a gas powered bicycle is a challenging, but an extremely rewarding task. Each motorized bicycle has its own uniqueness, but finding the right tuning is possible if you follow these five simple steps. You’ll be riding and enjoying the weather in no time.

Get Rid of Air Leaks

Air leaks or false air will destroy your gas powered bicycle’s motor performance. An average 2 stroke engine from China is simple, cheap and based on 1920's technology. These motors are not assembled to U.S standards, but that is what makes them affordable and a great entry point for gas powered biycleenthusiasts. During assembly, gaskets can be damaged and seals can be installed incorrectly. Examine the motor to see if there any leaks. On most 2 stroke engines, oil will seep out of places that air escapes. The most common places to look is in the head gasket, cylinder base gasket, exhaust gasket, intake gasket, crankcase gasket, engine seal, and the thin engine seal.

It is best to diagnose a leaking engine as soon as possible as it may prevent your motorized bicycle from running at all. Aneasy way to find air leaks is to spray a little carb spray around the various gaskets while the engine is running. If you hear a change in the engine’s idle, you have found your leak. The intake manifold to cylinder and carburetor to manifold are notorious for air leaks. Be careful when spraying carb spray on a running motor as it is highly flammable. We don’t want to sound like your mom, but remember, safety first. Always keep a fire extinguisher nearby in your shop.

If you are still unable to detect a leak in your gas powered bicycle, try checking for cracked or damaged parts. Sometimes the smallest crack will allow enough air to seep out, lowering the performance of your engine, and diminishing your ability to ride it.

Use the Right Gas

Using fresh fuel is essential for gas powered bicycle engine performance and longevity. Putting stale or old fuel can damage lower the performance of your bike. Filling the tank with fresh gas is a lot cheaper than buying an entire new engine for your motorized bicycle. As a rule of thumb, try to mix just enough fuel to fill your engine. Do not premix ahead of time as you will end up wasting a lot of gas this way. Old gas will varnish and gum up your carburetors and valves.

We are often asked what type of gas is best for your engine, we recommend regular unleaded. There is no need to buy expensive premium gas for a 2 stroke engine. If your engine is stock and unmodified, there is no need to use higher octane fuel. When mixing, always mix your gas in a gas can, not the gas tank for your motorized bicycle. When adding oil to the gas, use a ratiorite 2 stroke oil measuring cup to get the right mix. When an engine is new, strive for a 16:1 ratio, which is 8oz of oil per gallon. On a well-used engine, don't go any leaner than 32:1,which is 4oz of oil per gallon.

Using the right oil is also essential for prolonging the lifespan of your engine and ensuring that you get the best performance out of it. Avoid using cheap generic oils. The age-old saying of “you get what you pay for” applies here. Since these engines will get 75-125 miles per gallon, spending the extra money on better quality oil is not a bad idea. We suggest using a synthetic or synthetic blend oil. In our shop, we like to use the 927 oil made by Maxima, it can be found at most motorcycle shops.

Tuning the Carburetor

There are many ways to adjust a carburetor to get maximum performance. Jetting it is the best way to fine tune an engine. Most stock carburetors come with a .70mm jet in them. Depending on elevation, putting in the right sized jet is crucial to make a gas powered bicycle motor run properly. For example, at sea level, it is normal to install a smaller jet to get the most out of your engine. A size .66mm or .68mm is often the best way to go. A good rule of thumb is to try different jet combinationsuntil you find what works best for you.

When testing, avoid going too low (squeezing down) as this can cause damage to your equipment. Most carburetors for the 2 stroke China motors use a 5mm thread size. Only the CNS line of carbs use a different size (6mm). If your carburetor uses an adjustable slide needle, this can also be adjusted to increase the performance of your gas powered bicycle. Inside the carb slide,the needle will have a slide clip with several slot settings. Moving the clip up will make it rich, while sliding it down will cause it to run lean. Experiment to find the best setting.

Lastly, examine the color of your plug to indicate how your motor is operating. A light, whitish, ash color plug tip indicates the motor is good to lean, while a dark, oily, burnt looking plug tip indicates that you should tune it for a rich setting.

Adjust the Gears for Your Ride

The rear drive sprocket will determine your gas powered bicycle’s top speed or torque. Use the most appropriate gear for the type of riding you will do. Most motorized bicycle kits come with a 44 teeth sprocket. This is a good all-around gear. Generally on a 26" rear wheel, the more teeth you have, the more torque you will get, while less teeth will result in a highertop speed. Remember, if you gain top speed, you will lose torque, and vice versa. For example, using 36 teeth to increase your speed would result in a slower takeoff. Typically, gearing revolves around maximizing each tooth on your sprocket for an individual mph, but this is a general guideline that’s not alwaysexact. Another thing to consider is the weight of your rider. Bike weight and terrain will also factor into what top speed a gas powered bicycle can achieve.

If torque is what you’re after, you should go up in teeth from 44. If you want to climb steeper hills, tune your bike’s gears to betaller. A small bicycle engine will only put out so much torque. They are not motorcycles. Another factor that affects torque is the type of sprocket setup you install. Naturally, a more complicated sprocket is more difficult to tune. The 9 bolt rag joint stock equipment is the hardest to keep true and most likely to cause problems through prolonged use. A clam shell type bolt on solution is recommended to keep your wheel more reliable and to ensure that it operates safely.

Spark Your Gas Powered Bicycle

One of the easiest ways to get your gas powered bicycle engine to run in perfect tune is to efficiently burn your fuel. The proper spark plug gap is the first place to start. A motorized bicycle’s spark plug gap should be 0.6mm or 0.024". Most stock kits from China come with plugs that have no cross reference number on them, but they would be considered closest to an NGK B6HS plug. The number indicates the plugs heat range. A higher number plug would be a colder burning one, like the B7HS or B8HS, while a NGK B5HS would be the hottest plug you can run. Plug temperatures can affect the way a motor runs and the outside temperature also has an effect on it. Run a hotter plug in cold weather and a cooler plug in hot weather.Simple right? Never run a bike with an engine on it in the rain. The internal magneto will suffer from water damage and more than likely fry. Keep it dry at all costs. A high performance CDI is also another way to get a better spark. The Jaguar adjustable CDI and Jet Pack performance CDI are good products to try on your gas powered bicycle.

Piston Bikes Knows Gas Powered Bicycles

There are many high performance and custom parts on the market to make your gas powered bicycle faster and more reliable. From CNC race heads to the different carburetor options available, Piston Bikes has you covered. We offer international shipping to all of our customers and we are readily available to answer any questions that you may have about gas powered bicycles, bicycle engine kits, and anything related to our industry. Feel free to contact us through our website or toll-free by phone at 1-800-361-5755.

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