Dirt Bike FAQ

Ok, most def a 125 is too small for you, 250cc is about what you need, If your looking for speed get a 2 stroke engine with a power band and a jetted carb. If your just looking for something to ride casually and you don't want to show-off on it, get a stock 4 stroke.

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.

I'f your just starting out riding dirtbikes and don't know how very well DO NOT GET A 2 STROKE.
Start out with a 4 stroke or you might kill yourself, fast dirbikes are very dangerous, I know from experience.

other than that a 125 is too small for you, I have a 250 and I'm 5'8'' 155lbs.

Well there are a few variations on "pit bikes" but here goes with the basics. At off road races down here in the Dist 38 area, pitbikes are/were just that, little bikes for getting around in the pits between races or when getting ready for a race and your main machine was getting worked on to get ready for the race. They were anything from old Honda Z50's to little XR50's, to Yamaha PW50's etc. These days they are selling so-called "pit bikes" at Kragens and places like that that are made in China, with up to 110cc engines and questionable reliability. More little mini-bikes than anything you could use on a regular basis, they are copies of Japanese bikes in all respect except the reliabilty, not really suitable for long term use in the desert, and not really meant for the street, they are just parking lot toys for semi-grownups. The shocks arent really suitable for offroad, they just have big springs to look like they are, so if you are thinking of buying one for something like that save your money and buy a real offroad bike that you can learn on for reasonably cheap like an older XR200 or CR125. At least they have the underpinnings of a real machine on them.

Folks – the reason the asker is looking to do this mod is because AMA now has a class for the 105cc modded 80's and 85's.

To be competitive in this class, and since no manufacturer is currently offering a 105cc model, this is the only option.

Standard cylinder on this enigne in nikasil. No sleeve.

To do a big bore kit you will either need to have a liner installed in the cylinder (not the most reliable option usually), or purchase a complete kit which includes a bored and re-nikasiled (or other plating) cylinder.

Because of the change in cylinder volume, standard porting will NOT work. The porting needs to be matched to the new engine displacement.

You can purchase a complete setup like this from shops like Lukes http://www.lukesracing.com/luksr/cr85bigbore105p04.htm

Another option which will actually give much better overall power is an increase and bore and stroke to the new 105cc AMA limit. It's more expensive, but will give at least 20% more torque and midrange power than just a bigger piston.

Companies like Max Power offer these kits http://www.maxpower-engines.com/big-bore-kits/cr105.htm

He'll have to also remember that putting this much more power thru the engine can result in decreased lifespan of transmission and clutch components. Just something to keep in mind!

You looking to ride on trails or on a track.

There are 2 kinds of engines.
2 stoke (not sure if they are sold new anymore)
4 stroke.

A 2 stoke 125 has the same power as a 4 stroke 250 – basically.
All 2 strokes are on the way out.

So assuming you will only look at a 4 stroke – maybe a 250 or less would be ok for you. You have to find out the stand over seat height if looking at used bikes…and make sure you can reach the ground.
A 125 4 stroke would be best to learn on but you will outgrow it in a couple years….not from size but from power – you will want more proably in a few yrs.
Buy a used bike for your first one – then after you learn and get better then get a nicer bike.
Dont forget the helmet and be safe.

Nothing special. You need to stick with whatever's already in there, or do a good flush. You can get some nasty results if you mix the wrong types. Dexcool is good for high temp engines like a bikes.

Yep, alot would depend on his height and his riding experience…

if little to no experience, it would be best to start him off on a mild 4 stroke trail bike, like a Honda CRF80/100/150F (not R) or a Yamaha TTR90/110 or a Kawasaki KLX90/110 if those aren't too small for him. or if he is taller, CRF230 or TTR230 which are mid sized height wise but tend to be on the heavier side. these are all air cooled, older designed and bullet proof engines with moderate (at best) brakes & suspension but great bikes to learn how to ride on.

if he has some experience and is more agressive, something like a CR, KX, RM, YZ 80/85/100 or CRF 150R small wheel or expert (depending on his height) which will have all the performance upgrades including suspension & brakes.

if he is 5'6" or taller, he might be able to fit a full size bike…

again, little to no experience, XR, KLX, WR, CRFX 250

or if some experience and/or agressive, CRF, YZF, RMZ, KXF 250…

I would advise to start off used to save yourself some money as he might quickly outgrow or loose interest… then once he finds what really fits him, then you can always upgrade to newer…

They all do. Are you looking for specific size motor or brand?

All Jap manufacturers recommend 32:1 for all their 2 stroke engines.

Wow, This is a good question.

Solo machines have engines ranging in displacement size from 50cc to 650cc. In the early years of motocross, the 500cc class was considered the premier division. However, as technology progressed, the open class bikes became more powerful and fewer riders were able to ride them at their limits. The 250cc bikes also became faster with newer technology and were more manageable thus, they eventually superseded the 500cc bikes and became the premier class.

The most common distinction between motocross machines is whether they have two-stroke or four-stroke engines. Originally all bikes were four-stroke (in the Pre-65 era), but as the two-stroke engine improved they became more popular with their domination of the sport in the 1970's, 80's and 90's. The two-stroke engine produced more power than a four-stroke engine of the same capacity (cc), however oil must be introduced into the crankcase space for con-rod bearing lubrication, either with a pump or by mixing it with the petrol; this oil is burnt, giving the characteristic smell of a two-stroke engine. Four-stroke continued to be raced in specialist classes throughout this period, partially in the 500cc class. During the early 1980's another wave of technological advancement saw the typically two-stroke air cooled, twin shock rear suspension machines replaced by machines that were water cooled and fitted with monoshock rear suspension. This created even more powerful machines within the existing displacement categories (125,250 and 500cc).

The late 1990's saw an environmental crackdown on two-stroke engines particularly in the large American market. This spurred the development of environmentally friendlier four-stroke engines. While producing less power for the same displacement, four-strokes typically burn the fuel in a cleaner fashion. A major drawback of this is that four-strokes produce a deeper sound compared to two-stroke, which has led to a sharp rise in sound complaints across the world. To make the four-stroke competitive the world sanctioning body amended the displacement categories so that a 125cc two-stroke would compete against a 250cc four-stroke, and a 250cc two-stroke would compete against a 450cc four-stroke. By this point, the 500cc class had been dying out due to their immense power permitting fewer riders with enough talent to ride them at their limits. Yamaha introduced the first "modern" four-stroke with the YZ400F, which was soon succeeded by the YZ426F and then by the "standard" 450cc machine. Other manufacturers soon followed suit, downplaying their 250cc two-stroke bikes. As development progressed the power output of these bikes superseded their two-stroke equivalents, further sealing their fate. The four-stroke revolution continued with a wave of 250cc four-stroke machines to compete against the 125cc two-strokes. Once again manufacturers have been quick to promote these machines against their 125cc two-stroke equivalents. In the summer of 2006 Honda launched the CRF150R to compete in the 85cc class. This required sanctioning bodies to make further rule changes, which are very contentious with fans of two strokes.

For 2008 the MX2 class in amateur racing allowed 144cc two-stroke bikes to race against the 250 four-stroke bikes. This was to encourage more riders into the sport as two-stroke bikes are much more cost effective than four-stroke bikes. In AMA amateur racing two-stroke up to 153cc are allowed to race. But some countries like the UK only allow factory made or bored out 125's up to 144cc.

In professional racing 144cc machines are allowed but they have to be produced as 125's and then bored out to 144cc. This is to deter professionals riding from two-stroke bikes.

Youth racing included the MX2 class through to Autos, Adults ride MX2 through MX1 to MX3.

Motocross machines have extensive suspension to enable riders to tackle large jumps and ride at speed over the rough terrain. The advent of improved suspension transformed motocross from its scrambling origins with natural track to the current form today, with multiple jumps that would have previously been impossible.

To bring the weight down to an acceptable level (usually 200 to 250 lbs for full-size machines), items such as speedometers, lights, kickstands, electric starters, etc. are omitted. Lightweight materials such as aluminum and magnesium are commonly used as original equipment from the factory or sold in the after-market.

Because of the physical nature of motocross, riders spend much of their time standing to absorb shock with their knees. The long, flat seat is designed to allow riders to shift their weight quickly to provide more traction in corners, rather than for comfort.

Unusually for racing machines, motocross bikes can be purchased in a ready-to-race or nearly ready-to-race condition at moderate prices from major motorcycle manufacturers. Many riders, however, modify their machines further, both for outright performance and to have the bike's behavior more in tune with their own preferences or just for enjoyment

The National Sport Health Institute in Englewood, California tested several professional motocross racers in the early 1980s as part of a comparative study of the cardio-vascular fitness of athletes from various disciplines. Athletes from track, American football and soccer were tested, among others. The cardiac stress and strength test results compiled there revealed that the motocross subjects had higher fitness levels than any other discipline tested. Motocross racers now get their heart rate up to around 180 to 190 beats per minute and hold it there for about 35 minutes. Another thing to consider is that they do this twice per day (Original article appeared in DirtBike magazine in 1980). A subsequent study by the University of Pittsburgh Medical Centre's Sports Performance Complex in 2002 reconfirmed the result with more recent motocross racers. The intense physical demand of motocross derives from the fact that the racer of the bike must keep complete control of a 200+ pound bike, while also maintaining their top speed throughout the race

Freestyle motocross (Freestyle Motocross), a relatively new sport, does not involve racing and instead concentrates on performing acrobatic stunts while jumping motocross bikes. The winner is chosen by a group of judges. The riders are scored on style, level of trick difficulty, best use of the course, and frequently crowd reactions as well.

One stunt performed is the backflip, which was disputedly completed on a 250cc motorcycle by Greg Chrin using a specially designed dirt ramp. Soon after this, Mike Metzger completed this stunt using a standard freestyle ramp and dirt landing.[2] More recently Mike Metzger actually did a Backflip over the Caesar's Palace Fountains.[3] Some consider the body varial 360 as the most difficult stunt being performed at this time. This stunt, also called the Carolla, was first performed by Chuck Carothers at the 2004 X Games. Prior to this, the backflip 360, or off-axis backflip, was widely considered the most challenging stunt. Another rider taking freestyle to a new level is Travis Pastrana. At the 2006 X Games, Pastrana performed the world's first double backflip (in competition).[4] It earned him the 2006 Freestyle Gold Medal. The double backflip is currently considered the most difficult freestyle trick.

The latest craze is adult racing on miniature (50cc-125cc) motorcycles called minibikes or Pit-Bikes. The Pit-Bike concept was originally so that full size motocross riders could easily navigate the Pits, the area designated for parking, and setting up prior to an event. The craze grew from there. People began "hopping up" the bikes and racing them against each other. These inexpensive minibikes designed for small children are often transformed for adult use by adding taller handle bars, improving the suspension, exhaust, plastics. Other "hop ups" include larger, bored 75cc-192cc engines and reinforced frames. No standard definition of what constitutes a pit-bike by any major governing body exits, but the normal requirement is a 10"-14" front wheel, and a 10"-12" rear. None of the big 5 manufactures (Honda, Yamaha, Suzuki, Kawasaki, and KTM ) currently offer "race ready" pit-bikes, however some other companies are beginning to sell bikes designed solely for this purpose. These include Pitster Pro, OGM, Xtreme, the SDG, and Sikk MX. The minibike craze is predominately in Southern California, but has risen significantly in popularity in other areas of the US and the world. Pit-bike racing has taken a turn towards mini-moto (Supermoto) also, usually racing on go-kart and tight, small vehicle tracks. Riders usually wear a combination of motocross and street riding gear/leathers.

Supermoto got its start in the late 1970s as a fun side project for many road racers. Its first exposure to a wide audience came on the American television program ABC's Wide World of Sports in 1979. UK racing journalist Gavin Trippe envisioned a racing event that would prove who the best motorcycle racer was and from 1980 to 1985, he organized a yearly event called "The Superbikers," which pitted the top road racers and motocross racers against one another on specially modified bikes raced on special tracks on the television show.

I’ve had all four and there is no best brand. Some models are better than others. Because of air pollution laws, most new dirt bikes all have 4 stroke engines, these bikes are a little heavier than the older bikes with 2 stroke engines. The 2 strokes have great top end power but the throttle response at low engine speeds can be sluggish. This makes them more difficult to ride unless you have good skills. The 4 stroke engines would probably be easier for learning stunts even if they are heavier.