whitch one is
a Pocket Bike, Super Bike, or Ninja Bike?
Ninja Bikes, Super Bikes, Mini Bikes all fall under the general category of Pocket Bikes. Pocket Bikes are fully-functional, mini versions of regular racing motorcycles.
They are intended for Recreational Riding and Organized Racing purposes, and not regular transportation. Their well-built frame and body gives them a sleek look of a racing style bike. Top speeds range from between 25-45 mph, depending on the weight and height of the rider. Pocket Bikes are fully equipped with either a 49cc or a 47cc two stroke engine. Pocket Bikes come with front and rear disc brakes.
Pocket Bikes are made suitable for adults and for teens over the age of 16. They have hair-trigger acceleration, and must be operated by skilled riders only. Wearing a helmet and full safety gear is a must when riding a pocket bike. A child rider should always be accompanied by an adult or under parental supervision.
A 4 stroke engine usually has a distributor that supplies a spark to the cylinder only when it's piston is near TDC on the conpression stroke, ie. one spark every two turns of the crank shaft. Some 4 stroke engines do away with the distributor and make sparks every turn of the crank. This means a spark happens in a cylinder that just has burnt gasses in it. This just means the sparkplug wears out faster.
Most of what is written below on advantages and disadvantages of 2 strokes Vs 4 strokes is not actually correct! Take for example the lubrication issue of 2 stroke engines, sure small chainsaw engines may have the oil mixed with the fuel but this is not a direct result of the engine being a 2 stroke, this is just a result of someone designing a very simple engine. look at any large Caterpillar, or Detroit 2 stroke they have conventional oil sumps, oil pumps and full pressure fed lubrication systems and they are 2 stroke!!! also the argument about valves of 4 strokes Vs reeds and ports of 2 strokes is also incorrect. Sure some simple 2 strokes may use very primative systems to achieve the conrol of fuel/air mixture into the engine and exhaust out of the engine but again this is not a function of them being 2 stroke! I've worked on 2 stroke engines that feature poppet valves in the head (like a standard 4 stroke) - but they are definately 2 stroke - it's just that engines like this are not so much in the public eye - next time an ocean liner (ship) pulls into port check out its 2 stroke, turbo charged, direct injected diesel engine!! Finally the arguments of simplicity, weight, power to weight, and cost of manufacturing are not a funtion as such of 2 stroke Vs 4 stroke engines. The mistake of most of these commentaries is that they are comparing a simple chainsaw 2 stroke engine Vs a complex 4 stroke engine from a automobile - not a very fair comparision. As far as emmisions of 2 strokes - check out the Surrich/Orbital 2 stroke design that Mercury outboards are using - this is as clean burning as any 4 stroke.
The ONLY correct comparison below of 2 strokes Vs 4 strokes is that a 2 stroke can (in theory) produce twice the power of a 4 stroke for the same sized engine and the same revs.
As for the diagram [in the Snowmobiles episode of Scrapheap Challenge] - sure small 4 stroke engines do tend to "waste fire" the spark plug at the end of the exhaust stroke but this would not cause an explosion as depicted in the diagrams, but again here the idea of "waste firing"has noting to do with the 4 stroke cycle, rather it is a result of the simple design of a lawnmower motor. The diagrams should depict the inherant differances of a 2 stroke and 4 stroke engine. Hence one should show a firing every revolution and the other a firing every 2 revolutions.
TWO STROKE ENGINES
- Two-stroke engines do not have valves, simplifying their construction.
- Two-stroke engines fire once every revolution (four-stroke engines fire once every other revolution). This gives two-stroke engines a significant power boost.
- Two-stroke engines are lighter, and cost less to manufacture.
- Two-stroke engines have the potential for about twice the power in the same size because there are twice as many power strokes per revolution.
- Two-stroke engines don't live as long as four-stroke engines. The lack of a dedicated lubrication system means that the parts of a two-stroke engine wear-out faster. Two-stroke engines require a mix of oil in with the gas to lubricate the crankshaft, connecting rod and cylinder walls.
- Two-stroke oil can be expensive. Mixing ratio is about 4 ounces per gallon of gas: burning about a gallon of oil every 1,000 miles.
- Two-stroke engines do not use fuel efficiently, yielding fewer miles per gallon.
- Two-stroke engines produce more pollution.
-- The combustion of the oil in the gas. The oil makes all two-stroke engines smoky to some extent, and a badly worn two-stroke engine can emit more oily smoke.
-- Each time a new mix of air/fuel is loaded into the combustion chamber, part of it leaks out through the exhaust port.
Why 4-stroke beats 2-stroke
First some explanation on how the 4-stroke engine
When the piston moves down fresh air and gas is sucked inside the cilinder from the carburettor. When the piston moves up again the valves are closed and the air is being compressed. When the piston reaches it's highest position the sparkplug produces a spark that ignites the fumes and causes an explosion. Because of the power of the explosion the piston is pushed back. When the piston moves back up again the exhaustvalve is open and the fumes are pushed out the cilinder. Now the whole process restarts (exactly after 4 strokes. That's why we call it a 4-stroke engine...Duh!).
The 2-stroke engine works a little different. It performs 2 strokes at the same time (twice) so after only 2 strokes the whole process restarts. A two stroke engine uses the space above and below the piston. Below the piston are fresh gasses, above the piston these gasses are ignited. Assume the piston is in the lowest position with fresh gasses in the cilinder above it. When the piston moves up, these gasses are compressed, but at the same time teh airpressure below the piston drops and fresh air is sucked inside. When the piston is in it's highest position the sparkplug ignites the gasses and the piston is pushed down. About halfway down a channel from the fresh gasses to the exhaust gasses opens and a channel to the exhaust. Because of airpressure differences the fresh gasses flow inside the cilinder pushing the exhaust fumes out. Now the process starts again. As you can see this only took 2 strokes.
But which one is better?!? Of coarse "we" 4-stroke people say 4-stroke, but do you know why?? Probably not, so I'll explain. First I'll name some of the advantages of the 2-stroke engine over the 4-stroke engine.
What about the advantages of 4-stroke bikes? Are there any? OF COURSE! LOTS!!
Yeah, yeah, I know, 2-stroke bikes with the same displacement are faster, but look at it in another way. A 50cc racing 2-stroke engine will use over a liter per 10km. Now take a 4-stroke engine that uses the same amount of fuel. I guess you would end up with a 90cc or even a 106cc with a 26mm carb or something. No try beating such a machine with that crappy 50cc racebike thing :)
How to Read Your Spark Plug
|You can tell a lot by reading
your spark plug. Here's how to check your jetting by reading the plug.
Always start with a new plug that is of proper heat range and reach. Using
a plug with an improper heat range or incorrect reach can cause engine
damage or poor performance. Proper torque is essential as an improperly
tightened plug can damage the engine. Before removing any plug, clean the
area around it thoroughly to prevent debris from entering the cylinder. A
dry acid brush and an air compressor work great. Run the engine at least 10
minutes, as a new plug will not color immediately.
To obtain an accurate reading from a new spark plug:
It's best to use a magnifying glass to inspect the spark plug. The porcelain insulator (1) around the center electrode (2) should appear clean and colorless with a gray ring around the center electrode where it exits the porcelain. Metallic specks indicate lean jetting that is removing metal from the piston. Black sooty streaks on the porcelain indicate rich jetting.
In addition to improper jetting: