One of the more involved and exciting aspects of owning a pocket bike is the ability to soup-up or upgrade their performance. The first thing to figuring out what you should upgrade is to understand what you want (the second is deciding how much you’re willing to take apart and learn).
To get the most out of your pocket bike upgrades, make sure you understand the difference between torque and speed.
Torque is amount of force that your motor has every time it turns over. Generally, it is always a good idea to try to get more torque out of your engine above all else. If your engine can produce twice the torque than it did before the upgrades, you will reach your top speed at least twice as fast. The added torque means you can do wheelies, be the first off the start line, and accelerate ahead of the competition on every turn. And if you have more torque than you want, by simply changing the gearing (sprockets or pinion gear), you can get more top speed! Remember, torque means acceleration.
The top speed of your pocket bike is the first question we get from new riders. Having read about torque, I hope you understand that simply shooting for top speed is not as important as having the extra torque. However, having the fastest pocket rocket on the block is still much in demand. The top speed of a simple two stroke engine (which only has a single gear) is limited by the RPM’s of the motor. Typically, the motors will perform at peak power around 6,000 – 8,000 RPM. Depending on the size of your pinion gear, rear wheel sprocket, and outer diameter (circumference) of the tire, this will translate into a top speed achievable by the bike. Typically, new (unmodified) two stroke pocket bikes like the Blade 43R will achieve top speeds of 37 MPH. Riders weighing in excess of 200 lbs, riding on an incline (uphill), under-inflated tires, improper wheel alignment, over-tightened or misaligned brake calipers, and the surface conditions (gravel, sand, mud, moisture, etc) of the road can all decrease this speed.
While pushing the RPM’s is a sure way to get ahead, if you only focus the engine RPM’s for your pocket bike upgrades, you risk seizing your engine (melting it). This will require, at a minimum, a head rebuild.
Some parts, for example high performance clutches, are commonly thought to increase the performance of the bike. In reality, they do nothing of the sort, and while they may still help you win the race, a performance clutch doesn’t make your engine any more powerful and does nothing to your available top RPM’s. A clutch that engages later, or sooner, will simply change how much kick you get from your bike when you full-throttle it. We don’t discourage you from investing into performance clutches, just remember that you are not actually improving your engine performance or top speed in the process.
Best Performance Parts for Added Torque
Nothing adds pure torque better than a larger piston, or a higher compression piston. Believe it or not, most pocket bikes advertised as 47cc actually come with 43cc engines. We’re not sure why this is the case, but “true” 47cc engines are incredibly fast, and with the preponderance of younger riders getting into the pocket bike sport, it is probably due to child safety that manufacturers choose the smaller pistons. However, the 47cc designation stuck between the advertisers, so if you just bought a pocket bike and a reading this, more than likely you have a 43cc engine under the hood.
The difference between the two sizes is the size of the piston, measured across (diameter). They are 40mm and 44mm, respectively. By changing out to the 44mm piston an cylinder, you immediately gain an incredible torque boost that is very noticeable, especially for riders weighing over 140 lbs.
Equally effective at improving torque is the compression ratio of your engine. If you squeeze the air-gas mixture more before combusting it, you get a more violent explosion, resulting in more torque. Keep in mind that increasing compression puts more stress on the crankshaft and the bearings in the engine, so it is important that you have good parts inside your engine, and replace any damaged or worn-out components at the same time as working on your compression. So how do you actually get more compression? Well, if you have to ask, the only method we recommend is a high quality, made in USA, big bore kit. They come equipped with larger cylinders with stylish cooling fins. While they look cool, they actually serve a purpose – cooling the cylinder. A cooler cylinder also increases compression, due to the fact that heat causes expansion.
Chinese pocket bikes are known for carburetor issues. This is simply because they use very inexpensive carburetors. By investing in a higher quality carb, a larger amount of finer-mixed gasoline-air vapors will enter your engine, also increasing your torque. But you will not realize the benefits of a better carb until you couple it with a better exhaust. Two stroke engines are very sensitive to the shape and size of the pipe. A properly tuned exhaust pipe creates a sweet spot known as a power band, where your bike will lurch with an incredible amount of power once you hit a certain speed (RPM). A quality exhaust is shaped so that it creates a standing wave of exhaust gas inside of itself, sucking out exhaust and drawing in more air through the carburetor, increasing both torque and top speed.
Upgrades for top speed
Hop up kits specifically for top speed can be summarized with one word – gearing. By changing the pinion gear or the rear sprocket on your bike, you will change the gear ratio, and the same top RPM of the engine will be able to give you more top speed. You can do this by increasing the number of teeth on the pinion gear (9 is usually the max), or by decreasing the tooth count on the rear wheel sprocket (low 40′s is usually as small as you can go). Doing the reverse will give you more torque and is something that heavier riders or racers that need excellent hill climbing ability do. Changing your sprockets will probably require you to cut your chain and either add or subtract some chain links.
Another part known for adding top speed (without sacrificing toque) is a rocket key, also known as a timing advance key. It makes your engine fire earlier, and as you get up to higher RPM’s, it tricks the engine into going into overdrive. It also happens to be one of the least expensive upgrades you could do.
Fiberglass reeds, reed cages, juice boxes, high-flow air filters, even NOS kits can all add significant power and looks. But all these parts are an excellent way to experiment after you’ve done the tried and true combos of big bore, carb, and exhaust, known for the most noticeable power upgrades available for your two stroke mini pocket bike.