l may be gettin a rm 125 or yz125,but ive been told that u need to ride them like u stole them or theywill stuff up because its a 2 stroke, is this true???? if so wat other bike should l get, because all l will be doing is ridding on acres of land, but still wanna go fast...
im nearly 15, 60kgs and 175cms tall

Advantages of the two stroke:

Has more get-up-and-go because it fires once every revolution, giving it twice the power of a four stroke, which only fires once every other revolution. Packs a higher weight-to-power ratio because it is much lighter. Is less expensive because of its simpler design. Can be operated in any orientation because it lacks the oil sump of a four stroke engine, which has limited orientation if oil is to be retained in the sump.
These attributes make two stroke engines very popular for a variety of uses from dirt bikes, mopeds, jet skis, & small outboard motors, to lawn & garden equipment such as mowers, edgers, leaf blowers, chain saws & hedge trimmers.

But there r other differences between the two stroke & four stroke engines that r not so favorable, which is why u wo not see two stroke engines in cars.

Disadvantages of the two stroke:

Faster wear & shorter engine life than a four stroke due to the lack of a dedicated lubricating system. Requires special two stroke oil (''premix'') with every tank of gas, adding expense & at least a minimal amount of hassle. Heavily pollutes because of the simpler design & the gas/oil mixture that is released prior to, & in the exhaust (also creates an unpleasant smell). Is fuel-inefficient because of the simpler design, resulting in poorer mileage than a four stroke engine. Has a high-decibel whine that may exceed legal noise limits in some areas, depending on the product & local applicable laws

A two stroke needs to be ridden hard to get the best from it as the power band is so high in the rev range. They are best suited for tighter tracks over long flat plains like a big paddock. Four stokes have come a long way but are a bit more user friendly.

Whether u r riding on a motocross track or through a field, u must keep a 2 stroke high in the RPM is to avoid fouling spark plugs & allowing carbon build up in ur cylinder. If u r an aggressive rider then the 125 will be fine, but if u also want the option to just cruise at low speed & RPM from time to time the 125 is not a good choice. A 250F is faster than a 125 2 stroke, corners better than a 125 stroke but still gives u the option of playing around at low speed without fouling a plug & also gives u usable power from idle all the way to red line. A 125 2 stroke concentrates all of it is power in a fairly small RPM range (power band) which really only makes it a good choice for motocross racing where u will keep it wound out almost all the time. The statement made in the first answer about a 2 stroke making twice the power is true, kind of. The fact is a 125 2 stroke races aginst 250 4 strokes & so on, so it really does not matter. Also the 125 cannot touch a 250F in a race. You will pay a little more for the 250F, but after many years of racing 2 strokes, now that l know what it is like to race & ride a modern racing 4 stroke l will never own a 2 stroke again. l can not even begin to explain how much better they are, u just have to ride it to believe it.

A 125 would make a good bike. if the bike is running good then it wont foul plugs every 2 seconds. l have a rm250 & l have put around 25 gallons of gas through her this summer & l changed the plug once, & it did not need to be changed. l switched over to vp racing fuel for the north east grass drag series & l decided to change the plug before the races. l also go rode riding with my girlfriend. With the two of us on my bike im just putting along in 5th. We go riding for over an hour of just the put put putting & my bike has never dreamed about fouling a plug. also the 2 strokes r fast, get a full set of pipes, reeds & it will have plenty of power. 4 stokes r really expensive if they break!!!!!! l was riding a friends 2006 crf 250 & it happened to throw a valve when l was beating on it. then $1000.00 later he got is bike back & running good. later that week the bike seized the crank.. another $1000.00 later, it was good to go. Then later that month the bike just blew up again. He did not do the motor work himself, he took it to a racing shop each time.. if he had a two stroke he could have replaced the motor 3-4 times & still spent less than that stupid honda. yamaha makes the best two strokes