The Best 2-Stroke Motorized Bicycle Upgrades

Q: How can I make my motorized bike safer?

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A: If you want to make your motorized bike as safe as possible, it's vital that you start by adding lights to your bike and upgrading your wheels:

• Lights have a dual purpose: head lights help you see the road in front of you; while tail lights, turn signals, and wheel lights help you stay visible to drivers and other riders.
• Upgrading your wheels with heavy duty spokes and hubs will ensure they withstand more weight than ever, and they'll be able to travels safer for longer at high speeds compared to regular wheels.

Q: What precautions should I take before I upgrade my motorized bike?

A: The first, and probably most important, thing you should take into consideration is whether the upgrade you have in mind fits your motorized bike.

• Ensure parts like wheels and lights are the size compatible with your bicycle. For example, lights should be mounted snug against the bike; and when replacing wheels, ensure your motorized bike wheels are the proper size and not smaller/larger than what you're using.
• Also ensure that any bicycle motor upgrades are compatible with your engine. For example, ensuring the mounting ports of an exhaust line up or a carburetor fits properly onto its manifold.

The next thing you want to do is ensure that any upgrades you make to your engine are tuned properly. It's worth mentioning again that when you upgrade one component of your engine, there's a chance you'll need to tune or adjust other components.

• For example, if you upgrade your carburetor you'll be giving your engine much more fuel and air. That means you'll need to adjust the fuel jets inside to compensate.

So when you start upgrading your engine, make sure the components you choose are fit your bike, your bicycle motor, and you know how to adjust components of your engine when the time components.

Q: Do I need to upgrade my motorized bike?

A: If you plan on using a motorized bike for racing, commuting, or going off-road, you're going to want to upgrade components on your bicycle motor.

Don't get us wrong, a stock bicycle engine and simple motorized bike are fun and great for riding every once and a while. But if you want to push your RPM's to the max or you want to build a commuter, you're going to need to enhance your motorized bike's performance.

The higher the performance your motorized bike has, the more safety it should have as well. That means making sure your bike can physically and mechanically take all the performance upgrades you've made. Moreover, that you can see and be seen while you're riding.

As you can see, unless you plan on leaving your motor as a hobby project, it's time to start considering upgrading your bike. And that all starts with our list of the best upgrades for your motorized bike.

So what are you waiting for?

Operation and Maintenance of Your Motorized Bicycle

HOBBY. Gas bikes are for those who like to tinker, build and work on their own bicycle. These bikes are kits and not meant for consistent, reliable use. You have to maintain them regularly. Bolts come loose and the 2-strokes depend on un-burned oil for lubrication. That means they can be oily and messy. Approach your bike like a hobby and you will be pleased with the results. Beware, these engines come in myriad variations and levels of quality. Generally, the less you pay, the lower the quality. 

BREAK-IN PERIOD. All new gas bike motors require a break-in period. Break-in is 100-150 miles or five-ten hours. During this time, you need to run the motor with a special break-in 2-stroke oil, mixed at 20:1 (that's 6 1/2 ounces of oil per gallon), (for 4-stroke, special crankcase oil). If not break-in oil, then use 16:1 (that's 8 ounces of oil per gallon of gas). We recommend only using Dumonde oil, especially during the break-in period. We carry Dumonde Tech oils. Dumonde Tech Break-In Oil is designed for proper Break-In on any type of engine. Proper Break-In determines both the short-term life and longevity. It helps the rings seat properly and the cylinder walls to harden. Dumonde Tech Break-In Oil is a very complex formula that allows proper ring seat, work hardening, while impregnating parts with a matrix compound film to protect surfaces against lean periods and corrosion. Through research it has been found that a high percentage of these processes are not achieved with conventional oils. By not achieving these effects, performance and durability can be greatly effected. 

RUNNING. During break-in, do not run the motor for extended periods at a constant speed and do not run at full speed. Target less than 20mph and less than 30min. Always take a few minutes at an easy, unloaded, speed to warm up (3-5 min). On cold days, use about 3/4 choke to start (up is choke on and down is choke off). Learn to turn the choke off while going slowly. On warmer days, no or little choke is needed. For the first few rides, make them shorter and take time after each ride to inspect the bike, tighten all the bolts and chain and make sure everything has settled in for the long-term.

2-STROKE OIL. After break-in, continue to use synthetic oil at 32:1 (that's 4 ounces of oil per gallon). Using synthetic oil extends the life of the motor and makes less smoke. Do expect some burned oil accumulation at the tail pipe (residue). This is normal. If you use regular 2-stroke oil, run at 20:1 (6 1/2 ounces per gallon). The typical "peanut" gas tank that comes with most gas bike kits are 1.5 Liter or 0.4 gallon (51oz). (In a pinch, that's 2.6oz of regular oil or 1.6oz of synthetic.) It is not recommended to mix the gas in the bike's gas tank. It's difficult to calculate the right mixture because residual pre-mix remains in the tank and you may not get a good distribution of oil before running.

4-STROKE OIL. On your 4-stroke crankcase oil, use a good quality, 4-stroke-specific, motorcycle oil. 15-40 is fine, such as the Dumonde GP4 and the Dumonde  B4 break-in oil for the first 100-150 miles (or five-ten hours) of operation. Synthetic is always a good choice. For best longevity, change the oil every 10 hours of use. This will ensure top performance and wear at all times. It doesn't hold much oil and has no filter, so it is best to change it often. 

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FUEL. It is best to select a small gas can to mix your fuel. The best choice would be a red, steel, 2-gallon storage can, Certified by FM, UL/ULC, and TUV. This will keep your fuel fresh and safe for at least six months. Use fresh premium gas on 2-strokes. Regular is fine for the 4-strokes. A plastic container, certified for gasoline storage is OK, but the gas will need to be used in less than three months. Mixing in a gas can also lets you be more precise on your oil measurement. 

2-STROKE STARTING. To start the motor, set the choke and turn on the gas. Squeeze the clutch and hold the throttle at 1/4 open. Pedal the bike up to at least 5mph. Release the clutch in a smooth continuous motion. If you slow too much before the engine starts, start over. Allow the engine to warm up at around 10mph. Running at 20mph allows the combustion chamber to stay hot and the motor to stay in the optimum power level (best gas mileage too). Avoid idling for more than a minute or two. Un-burned oil accumulates on the spark plug at an idle and could foul the plug (engine will not run). Idling puts excess strain on the clutch and the lack of air flow could overheat the engine. If you come to a stop light, use the clutch. If the wait will be a while, stop the engine. Never run the engine at speeds under 5mph (lugging). Most riders get in excess of 75 miles per gal of gas. 

2-STROKE ELECTRICAL. For proper operation, the spark plug should be clean and not fouled by oil. The gap is 0.14. Use a B5HS or B6HS model plug. The magneto provides the electrical pulse to the CDI for a spark. The magneto should measure around 300 to 400 Ohms while disconnected. Always ensure the magneto is dry and the mounting bolts secure. Check for frayed or grounded wires - especially leaving the housing. Your CDI inputs should have a low resistance, around 10 Ohms, but you may need to make measurements with the "diode" setting to ensure accurate readings with a digital VOM. Checking for spark: With the gas turned off and the carburetor bowl empty, check for spark in a dark area by removing the spark plug, grounding the side of the plug, and turning the engine over rapidly. Make sure the connections are good throughout the chain, black wire is connected to black wire, and no pinched wires. Disconnect the kill switch wires to make certain they are free of grounds (test with them on and off). You should see a sharp blue spark on every revolution.   

SMOOTH STARTS ON ALL BIKES. Do not use the clutch to start from a stop. The clutch on these motors is not suitable for standing starts. Pedal to start. In all cases, when starting from a stop, pedal to get some speed and, while pedaling, release the clutch in one smooth motion (add throttle gradually), after you reach 5mph. For 4-strokes motors with an automatic clutch, slowly twist the throttle as you gain speed.  Continue to pedal for a bit to help the motor achieve solid operating speed (about 10mph). Two-stroke motors have a power band that hits at higher RPMs. At lower RPMs (and especially at idle) the motor will tend to foul or "load-up." Once you hit the power band, the motor will "clean-out" or begin to run stronger and smoother. Lugging the engine should be avoided, as this will cause the engine to load up. These are not motorcycles. The motor is to help you sustain speed only.

2-STROKE CARBURETOR. It is absolutely essential that the carburetor be fully seated and have no air leaks. A poorly installed or loose fitting will greatly effect operation and adjustment. Worse, air leaks can cause a lean mixture and damage the engine. Periodically, check your intake and exhaust bolts for a snug fit, as these may vibrate loose over time, especially during break-in. You cannot diagnose or adjust the fuel system unless all the fittings are seated and sealed. 

Normally, all the carburetor settings do not change. The air screw on the side of the body of the carburetor adjusts how much air mixes with the idle circuit (Idle Adjuster). The standard setting is 3 1/2 turns out from fully seated. On the NT-style carburetors, the air screw is very a very simple design. Screwing the adjuster in makes the idle speed faster and richer (too far and the bike will load up and stall). The idle speed is set by adjusting the screw for optimal idle - just fast enough to not stall out. The cap Cable Tension Adjuster nut adjuster and throttle handle adjuster are used to take up the slack in the throttle cable and can be used to hold the idle. Because the throttle cable comes manufactured at a fixed length, all the pieces from the throttle tube down to the cap nut and slide must be correct or you will be too short or long to make adjustments. If any of these pieces become worn or damaged, they must be replaced to accurately adjust the idle. Use the Primer on cold days. If you are an advanced mechanic, look at your spark plug to gauge the running mixture. Move the clip on the jet needle up to lean out the mixture or down to make it richer. Check your spark plug after running at 20mph, at full operating temperature, for at least 1/2 a mile. It should be chocolate brown. If it is dark and oily, you may need the B6HS (hotter) plug or a leaner mixture. If it is white or very clean looking, you may need to make the mixture richer (lower the clip on the needle). Warning: Running a lean mixture may damage your engine.

After any changes to the intake or exhaust systems, you may need to adjust the fuel mixture. Better carburetors have replaceable main jets, providing a way to fine-tune the fuel-air ratio. If you install a high compression head, expansion chamber, reed valve, boost bottle, piston or any other change, it may be necessary to replace the main jet. All the better carburetors take standard jets that come in a kit, making it easy to try different settings. Once everything is working well, adjust the jet size based on top speed, the color of the spark plug and throttle response after half throttle. 

PARTS AND UPGRADES FOR 2-STROKES. The most effective way to improve throttle response, low-end power, torque and horsepower, is to add a few hop up parts to the fuel and exhaust system. An upgraded carburetor with better machined internals is a good starting point. Adding a reed valve will dramatically improve low-end and throttle response. On a 2-stroke, replacing the stock muffler with an expansion chamber will improve horsepower and torque, plus result in better top-end performance and increased fuel economy. After you do those changes, you may want to change the standard 42T/44T rear sprocket to a 32T/36T. When parts break, many are available, but sometimes it is cheaper just to throw the engine out and replace the whole thing. After all, a complete kit is under $300 and you can get engine-only kits for even less.

EXHAUST.  All of the engine kits come with an inexpensive muffler. Over time, these will rust internally, restricting air flow. Even the best mufflers will rust. Periodically, you will need to replace your muffler to maintain good air flow. To run best, engines need some restriction or back pressure, usually regulated by the muffler exit opening. Running without a muffler, or with the exit restriction removed, will certainly be louder, but universally yields less horsepower. Pick the right muffler for your engine to ensure the right amount of back pressure and good air flow. 

SPARK PLUG & AIR CLEANER MAINTENANCE. On all bikes, replace your spark plug every 500 miles or 25 hours of use. Gap to .14". You may go longer, but do risk poor combustion or a fouled plug. Clean the air filter every 100 miles or five hours. Clean it with solvent (paint thinner or kerosene) and do not oil it. Replace the filter whenever it becomes torn or ragged.

CHAIN. Most commonly, 4-stroke motors use a 420 chain and 2-stroke motors use a 415 chain. The rear sprocket is never perfectly centered, so adjust the tension based on the tightest place on the rotation. The spring tensioner can help maintain tension when you want the chain tension uniform across all of the rotation. Be careful not to over-tighten the chain because it will cause excessive wear on the drive bearing. Make certain you position the master link so the clip faces in the direction of travel that would push it into place while rotating. Keep your chain oiled, but clean - don't goop on oil, as it will attract too much dirt. The most common problem with the chain is maintaining a good chain line. If the chain line if off, the chain will climb the side of the gear on the wheel, derailing and falling off, often jamming into the wheel or breaking the chain. Adjust the tensioner so it guides the chain onto the wheel gear accurately - check the chain line before every ride.

BEFORE YOU RIDE. Before every ride, check bolts on both the bike and motor for proper tightness. These engines vibrate a lot and do wiggle loose. Do not over-tighten bolts as they do strip easily. If you have spoke wheels, check every spoke for tightness, especially on your rear wheel. (Note: starting off smoothly vastly improves wear on rear spokes.) Oil your chains with Dumond Tech chain oil as needed (usually every 100 miles). Wipe them clean after oiling. Check and adjust the chain tension. Riding any bike carries with it some risk of injury. Remember, you are responsible for the safe operation of of your bike. Take time before every ride to ensure it is safe to ride. Wear a helmet.

CLEANING. To clean the bike, spray with a good degreaser, scrub and wash with warm soapy water. Sprinkle the soapy water off, never spray. Keep water out of the exhaust port and carburetor. It is best to bag the carburetor prior to washing. If you operate the bike in the weather, rinse it off after you get home. Water gets into the bearings, so keep it clean and dry after use.

TUNE UP THE BIKE. Every year, or sooner if you ride a lot or in the weather, give the bike a good cleaning. This would include servicing all the bearings (wheels, headset, crank, chains, tensioner, brakes, etc.). Usually, the engine only needs the air cleaner and spark plug checked. Keep water out of the engine area or be very careful not to spray water into the engine area. 

NUTS AND BOLTS. These kits all vibrate a lot. The nuts and bolts need constant attention. If you replace a fastener, clean it thoroughly and apply Locktite. Be careful not to over tighten any fastener as none of them are specifically hardened. You can buy a stainless kit with Allen head bolts to replace many of the common maintenance areas. This helps to get them on and off, instead of the Phillips head, and improve binding with less corrosion.

STORAGE. Store your bike in a covered, well ventilated area, suitable for a gas-operated vehicle. Never bring it indoors or into a living space. Always shut off the gas tank petcock (item #4 in the exploded view). For extended periods of storage, carefully drain the carburetor bowl and dispose of the fuel properly. Premixed gas may be stored up to six months if it is in a steel can with little or no air space. 

WEAR. Over time, your engine will degrade and lose power. These engines, if operated properly as described above, will last 200 or more hours. When they do wear out, it is usually far cheaper to just replace the engine. Engine-only kits are less than $200. However, parts are available for typical wear items, like the clutch, spark plug, electric connections and carburetor, which need regular maintenance.

MY BIKE WON'T RUN. Fuel that is over three months old may be a problem. Check for a fouled spark plug. Replace it if it is crudded up. Pull the plug and rotate the engine by hand while grounding the plug on the head. The spark should be bright blue. Make sure the magneto is clean and well grounded. Check the resistance of the CDI (400 Ohms) and the magneto (10 Ohms). Check the carburetor for small bits of rust that can clog the idle jet, main jet and float bowl. Carburetor contamination is a very common problem. Tighten the head bolts to spec. Lastly, check for compression. If low, replace the cylinder, piston and rings or, engine-only kits are cheap, just replace the engine.

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