Dirt Bike FAQ

Maybe….it would weigh less…but sound terrible.

There's no replacement for displacement. Power costs money. Bore it out and mike it bigger. Good Luck and happy trails.

Drain carb , drain engine oil, clean air filter drain filter box if water present ,drain gas ,and dont let it happen again my little water nipper

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.

Why don't you have it rebuilt. powroll in
oregon has a lot of go fast goodies
for the xr100. just because it was raced
does not mean you need to replace the
complete engine.

Way more trouble than it is worth.
requires:

Modification of the charging system and connection of a battery.
Wiring of lights, head+hi-lo, brake ,tail ,marker and turn lights and all the switches that go with them including a breaker panel or fuse box.
Street legal exhaust and appropriate engine de-tuning.
Street legal tires ( Knobs are no street legal)
A key ignition.
In most states ,fender height on MX bikes are too high and need to be lowered.

And there is no "Cheating" because the bike will have to pass a physical inspection before it is licensed .

I've done a couple, A Honda XR500 and a Yamaha IT425.

Even though it's not what you want to hear ,my advice is to get a dual purpose and "trick it out" rather than trying to make a MX bike street legal.

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.

To shift the gears on a motorcycle there is something important you should learn from the service manual and that is just exactly how many gears your bike has. Most bikes have either 4 or 5 gears. Modern Sports Bikes have 6 gears.

First put the bike in neutral, it is half way in between 1st and 2nd gear. Squeeze the clutch ( found on left handle bar) before trying to shift. You will know you are in neutral if a green light is showing on your gauges or if the bike rolls freely with the clutch out. Once in neutral you can start the bike, but keep the clutch in. According to your bikes shift pattern (Standard or GP Shift) you then shift into 1st gear by pushing the shift pedal up or down. Slowly let out the clutch while simultaneously increasing your RPM's with the throttle. The bike should start moving forward and as it does, release the clutch completely, but stay on the throttle. Once the bike is moving you can roll on the throttle to increase speed. As your RPM's increase you will need to shift into a higher gear; to do this you will need to squeeze the clutch in again. Then according to your bikes shift pattern, go to the next highest gear. Now release the clutch and roll on the throttle. To down shift you squeeze the clutch and shift to the next lowest gear, release the clutch. Be sure to match your RPM's to the wheel speed on a downshift or your rear tire can lock up resulting in a high-side.

There are currently two shift patterns on modern motorcycles, standard and gp. Standard shift is well…standard, it will be found on most motorcyles. GP shift refers to the shift pattern used by professional racers. GP shift is reversed so that a rider does not have his foot under the shift pedal when needing to up-shift in a corner, it also makes for faster up-shifts. GP shift is primarily found on sports bikes and bikes intended for use on the track, but most sport bikes come with standard shift from the factory.

Shift patterns are set up as follows…

- Standard Shift (starting from neutral):

First gear is down 1

Neutral is up one and it is indicated by a green light on your bikes gauges. If you are not sure you are in Neutral ~ it is the only time when your bike will freely roll backwards when the clutch is not engaged.

Gears 2 ~ 4/5/6 are all up.

- GP or Reverse Shift (starting from neutral):

First gear is up 1

Neutral is down 1 and will likewise be indicated by a green light on your gauges.

Gear 2-6 are all down

Shifting gears on a motorcycle may seem awkward at first, but try it a few times in your garage or drive way with the bike off. Roll on the the throttle and practice using the clutch to shift up and down. If while riding you start going to fast or you feel as if you are not in control, pull in the clutch to disengage the engine from moving the rear wheel and apply brakes accordingly. Within a short time shifting through the gears will be second nature.

Yes.

If you try to take off in 3rd gear you're going to stall. Do it too many times and depending on your bike you're going to wear out the clutch faster/prematurely.

And check http://www.sportrider.com under the riding techniques section theres a article on "blipping" the throttle on downshifts.

Blipping the throttle on downshifts is just matching the RPM of the engine when downshifting with the clutch in upon release. It makes it smoother.

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.