Dirt Bike FAQ

–It could be a bad pulse coil. It's at the flywheel and acts like a set of points. It sends a signal to the CDI. The pulse coil could be bad or unpluged.
–Could be a bad CDI box.
–Could be a bad kill switch. Always in the off position. Dirt bike kill switches are cheap and easily damaged in a fall. Try unpluging it (it's a grounding switch).
–Could be a bad ignition coil. Easily tested with a multi-meter.
–John B gave a good answer about the spark plug cap not making a good connection. Unscrew it from the wire. Cut 1/4" off the end of the wire and screw it back on.
–Could be a bad spark plug cap. Pull one off your car or lawn mower and try that one.
–Buy a shop manual to learn all the tests to perform and the specs each test should give.

http://www.motocom.com/motorcycles/

I share your interest in a truly lightweight dirtbike but my riding habitat is federal (military) land so my bike has to be street legal and plated. My current ride is a Kaw KL250 (Super Sherpa). It's a nice bike but too heavy for my needs. I'd really like to find something around 150lbs but that seems to be impossible. Some of the older Jap dual purpose bikes were less than 200lbs e.g. Kaw KE100 and Hodaka 100B+ but their suspensions are pretty rudimentary. Good luck on your search.

I'm not sure that the Chinese are quite as good at making engines as the Japanese just yet. I would stick to Japanese for piece of mind about spares and servicing. Though the bike does get some good ratings on the Internet about it being a good little racer.
I cant believe I just typed that. But Racing is Racing. even if its with small bikes.
its Quality of build will be answered over time, as with other Chinese imports

Ebay there is always someone parting out a bike. Or a cycle salvage yard. Most Go cart racers buy the carts with the engines or buy a new bike and sell the chassis and parts. They make carting engines Ive seen many on ebay and at carting shops.

Upgrading a disposable motorcycle is a waste of time. You don't need to buy a new 125cc bike, get one that is 2-3 years old and well maintained for less then half the original price. A 125cc bike will not be good for driving on the street unless you like in a rural area without highways. The age limit to drive depends on your state, I don't know Indiana's. You definitely will/should take a class to learn the laws of the street before riding in traffic. If the 125 you are looking to buy is a 2-stroke you need to work on your mechanical skills as the engines don't last that long.

What's the difference between a 2-stroke engine and a 4-stroke engine?
Gasoline and diesel engines are both available in either 2-stroke or 4-stroke versions

In a 4-stroke engine the sequence can be written:

Compression Stroke. The piston goes up and compresses a fuel/air mixture (in a gas engine) or just air (in a diesel).
Power Stroke. The fuel is ignited (by a spark in a gas engine, by being injected into high temperature air in a diesel.) The energy released drives the piston down. This provides the momentum necessary to keep the crankshaft turning and make the other three strokes happen.
Exhaust Stroke. The piston goes up and pushes the burned gases out the exhaust valve.
Intake Stroke. The piston goes down and draws in new air, or fuel/air mixture, ready for the next compression stroke.
In a 2-stroke engine, the last three strokes are combined into one.
Compression Stroke. The piston goes up and compresses a fuel/air mixture (in a gas engine) or just air (in a diesel.)
Power Stroke. The fuel is ignited and drives the piston down. As the piston goes down it not only turns the crankshaft but also pressurizes the fuel/air mixture in the crankcase which is about to be admitted to the piston for the next cycle. Near the bottom of the stroke, an outlet opens and the exhaust gases are released. Even nearer the bottom of the stroke, an inlet opens and new fuel/air (which was just pressurized by the piston) rushes in ready for compression.
Because a 2-stroke engine gets a power stroke twice as often as a four-stroke engine, it puts out about twice as much power (and makes twice as much noise) as a four-stroke engine of the same size.

The downside is that, because the 2-stroke engine is sloppier about how it expels exhaust and takes in fuel, doing them almost at the same time, it is more polluting. Also, the 2-stroke engine lets fuel into the crankcase, where the piston can pressurize it prior to intake. In order to keep the crankcase lubricated, you have to add expensive lubricants to the fuel, and even so, 2-stroke engines don't last very long.

So 2-stroke engines are used in chainsaws and lawnmowers, where power/weight is important, but the engine isn't used for long periods so pollution and engine life are less of a concern. The continuously used engines in cars and trucks are 4-stroke engines.

Hi Sk8,,,
I'm going to make a guess and assume it's a Chinese Clone of a little Honda engine.

Normally,,all those type motors are very easy to start if the engine is in Good Condition,,,or even fair condition.
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Some things that can make them hard to start.

*Low Compression.
That can be caused by several things.
You Really need to have the compression checked with a gauge to determine if it's within proper range.
Should be about 120 psi minimum.

If it's Less than that,nothing will really help much.

"Low Compression" is usually thought to mean "burned-up / wore out Engine",,,,and that's often true.
But not Necessarily.

Valve Clearance Adjustment,,and Timing Chain condition will affect it also and make the compression a bit lower.

>>>Adjust the Valves to .003"
That's Looser than recommended setting of .002".

>>>Make sure the cam chain is adjusted right.
Sometimes the adjuster "sticks" and doesnt really work right.
Also need to check the chain for wear.
Both things are easy to do.

CARBURETOR:
These things are so small even the Tiniest amount of gum/varnish/deposits will make them behave badly.
Easiest thing to do is try some Cleaner added to the Fuel tank.
Use FUEL INJECTION cleaner,,,not "carb cleaner"—it works much better.
Chevron Techron ,,or Seafoam are 2 good ones.
Don't Overdose it thinking that "more is Better".

You may ultimately have to remove the carb and take it apart to clean it.

The Intake Manifold "never" gets loose on original,genuine Hondas.
On all the Clones,,,,it's a crapshoot.
If they Do get loose the Gaskets will leak air,,and cause hard start,bad running.
Or,,if Carb has ever been removed ,,,it's tuff to get them to re-seal without using new gaskets.

Ignition System/Spark Plugs:
Most of the late model versions all have electronic ignitions.
They usually work OK,,,and are Usually NOT adjustable.
When they FAIL,,,almost always it fails like a Light Bulb.
They just Quit Working at all,,,,no mysterious misfires,,no intermittent problems that come & go.

So IF it sparks,,and eventually Runs,,,
there's 99% Odds the CDI Ignition is working OK.

Spark Plugs.
Try an NGK Iridium Plug.
DO NOT expect it to "FIX" anything,,or even Cover-Up any sort of problems elsewhere.
Make sure everything Else is in good order First.

They are NOT Magic Plugs,,,but they DO improve starting because they can fire under a much wider range of conditions,,including Weak Ignition system,,,or partially flooded,,,very cold temps,,,etc,etc

They're expensive ,$8~10.
It Wont FIX anything,,but they can definitely help

Get a Service Manual if you can.

If You cannot find one,,,early Honda 50 & 70 Manual is Close enough to give You general basics

…………………………………………………………..
You will have to register,,but You can get Free Manuals here

http://www.repairmanualclub.com/

These will help.
Remeber,,these are NOT Identical to Yours,,not even the same engines,,70's and 90's are Different.
But they can give you an idea how the things are laid out,,,and valve adjustment,timing chain stuff is basically the same.
Carb Clean/Rebuild PROCEDURE is sorta generic,,,things like that.

Consider them only HINT,CLUE,or GUIDE,,,,and NOT actual,accurate service manuals for Your bike

Honda S90-CL90-C90-CD90-CT90 Shop Manual

Honda SL70, XL70K1 Factory Shop Manual, English

Good Luck with it

I dont think a dirtbike 50cc engine is small enought to fit in a pocket bike. if you hav the engine just measure it, or if you know someone who is selling one aske them to take some measurments for you. you can always check ebay for pocketbike engines.

It's a 1986 RM250.A basket case is a bike that needs to be put back together.It says it's in good shape but it needs a new crankshaft.In other words the engine needs to be re built.They want 300 dollars or best offer.Unless you know how to re build engines and assemble bikes it wouldn't be a good choice for you.

LOL i loved the it has a basket case answers Too funny!

Most of them are 2-cycle engines, pretty easy to work on.

http://en.wikipedia.org/wiki/Two-stroke_cycle