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[[Old What to do when your bike won't start]]

What Do I Check When My Motorcycle Won't Start?
A motorcycle engine needs three things to start: Battery, Fuel, and Ignition. Any one of these three will prevent your bike from starting. We will address each of these, but remember that some of this information may not apply to your specific motorcycle.
While we cannot address every possible reason why it will not start, we can cover the basic things you can check yourself, with just basic hand tools.
In all cases, if you are not comfortable with getting your hands dirty and tearing things apart, then arrange for a reputable mechanic to work on it and save yourself the aggravation.
Many of us have had a brain cramp and overlooked that one really simple thing; and while these might seem obvious, before we get into troubleshooting, there are a few simple things you should check before you start taking your motorcycle apart.
• The fuel petcock is on, and there is fuel in the tank. • The ignition key is in the On or Run position. • The Kill Switch is in the Run position. • The transmission is in Neutral.
If the bike won’t start, you will have to investigate further.

'''THE BATTERY'''

The battery must be fully charged, especially if it is a new one. Most battery manufacturers recommend you slow charge the battery overnight. If you don't already have one, a trickle charger or Battery Tender is a good investment; as is an inexpensive voltmeter/multimeter.
With the engine off, the battery should read in the vicinity of 12.5 volts. When the engine is running, it must be rotating at roughly 1,500 rpm or faster before it will begin to charge the battery. With the voltmeter still attached, rev the engine and you should see a reading of approximately 13.5 volts. If it does, then the charging system is operating correctly. When idling, the motorcycle is running off the battery, and if you let it idle too long, it could exhaust the charge in the battery, and the engine may die.
If you press the starter button and the engine turns over, but does not start, then the problem is most likely NOT the battery. If you press the starter button, and nothing happens, then the battery may be dead, OR you may have neglected to do one of the basic things, like turn the key on.

'''FUEL'''
Make sure you have fresh gas in the tank, not some stuff left over from last years riding season. If you are not going to drain the tank for the winter, then make sure you use one of the commercially available stabilization products like Sta-Bil or Sea Foam.
If you have just tried to start the engine for the first time in a while, then the possibility exists that your carburetors may be gummed up from sitting. The appropriate amount of Gumout or Sea Foam may help; but if it doesn’t, you will probably need to remove the carburetors, disassemble them and clean the gunk out of them. Learn more about cleaning the CX/GL carburetors here.
Make sure the fuel petcock is turned to the proper position. You most likely have an On and a Reserve position on the petcock. If the tank is low on fuel, you may need to put the petcock in the Reserve position. If you have cranked the starter, and the engine does not start; check to see that you have not flooded the engine. I good indicator of a flooded engine is if you can smell a strong odor of gas near the carburetors. You can also remove one of the [plugs] (18mm deep socket) and check the electrodes to see if they are wet. If you smell gas, or the spark plug electrodes are wet, you may have flooded the engine. If so, then make sure the choke is Off, let the bike sit for a bit, and try to start it again, this time without giving it any throttle.
If you do not smell gas, and the [plugs] look dry, then you may not be getting any fuel. Your gas tank may be equipped with a fuel line filter, either near the petcock assembly, or somewhere in the fuel line itself. Check them to make sure they are not dirty or clogged; if so, replace them. Your gas tank may also have a vent line which may be plugged or pinched. If it is, the engine will not be able to receive fuel.
Remove the gas filler cap, and if you hear a hissing sound, like air being sucked into the tank, then the vent may be the problem. Try starting the engine again. If it starts, then shut it off right away and resolve the vent problem. There have been reports that clogged vent tubes have caused the gas tank to buckle or collapse due to the vacuum created in side the fuel tank by the blocked vents.
If everything looks OK, and you have a can of starter fluid or a spray can of carburetor cleaner, you can try spraying a small amount into your air intake, then try to start the engine. If it fires up, but then dies right way, then you are probably getting spark to the plugs, but not getting fuel to the carburetors and you may have to tear them down and clean them. Do NOT keep spraying stuff into the air intake; you may damage the engine that way!
If you still can’t get the engine to fire, then you may have ignition problems.

'''IGNITION'''
There are 2 basic ways to check to see if your plugs are firing. You can leave the spark plug installed, and pull the rubber boot from the plug. Stick a screwdriver into the rubber boot, making sure the end it touching the connector inside. Hold the shaft of the screwdriver about 1/8 of an inch away from the block and crank the engine. If the ignition is sending juice, you should see sparks jumping the gap between the screwdriver and the engine. This will tell you if the coil is delivering spark to the plugs, but it won’t tell you if the plugs themselves are bad or not.
An alternative method is to pull a plug, check to make sure that the gap is within the manufacturers recommended specification, and then connect the boot to the plug again. Hold the electrode against the engine, then crank the started and see if you can see spark jumping the gap of the plug. You probably want to hold the plug wire with rubber handled pliers, unless you enjoy getting zapped. The rocker covers do not make a good ground as they have rubber gaskets.
If you don’t see a spark, then you may have ignition coil problems, or other issues. Find the location of the coil on your bike, it may be under the fuel tank, and make sure all wires are connected correctly.
Using fresh gas, new plugs, choke in the off position, try starting the engine. If it still won’t start, then you will need to check for things that are outside of the scope of this post. If your motorcycle starts and stays running, then it’s time to celebrate and go riding. Don't get too far away from home though, just in case you missed something.

'''Sudden ignition failure of CDI bikes''' Written by Reg in Bristol
Standard CDI bikes have been known to suddenly stop with no warning and the rider finds there's fuel, but no spark on either side.
The tests to pin down the fault take less time to do than writing this short procedure. 
First disconnect the kill switch wire and try again. Its been known for the weather to get in the contacts under the kill switch knob and this can short ignition power to ground. (This is the black wire w/white stripe that goes from the CDI box, to the kill switch. Just unplug it at the CDI)
No joy? Under the seat are the stator and CDI connectors.
Open the 2 way connector that carries the blue and white wires.
A quick resistance test between the battery negative terminal (GROUND) and each of these will indicate if the source coils on the stator are OK. Never mind the others for now.
Quickest test is to measure between the the blue and ground and expect 500 ohms plus the slightly longer but more informative test is to check for 387-473 ohms on the white to ground and 77-95 ohms between white and blue.
Most people know this test by now, its the next bit that seem to go unheeded.
If the stator tests out OK, then its probably producing power for the ignition system and you need to see if the CDI box is handling this power correctly. The tests in the manual require specific meters few if any will have and are a long winded PITA anyway which tells us very lttle we can do anything about.
There's a quick and dirty test you can do with a cheap common as muck digital meter to see if the CDI is healthy.
I've done it many times to diagnose CDI failures quickly. Basically you need to measure the 'open circuit' DC voltage on the LT wires to the coils 'open circuit' means the wires are disconnected from the coils. Unless its an auto ranging meter, you will need to set the voltage range to 0-250V DC.
DC OK?

With the black probe clamped to battery neg and the red probe stuffed in an opened Coil wire bullet connector, crank the engine on the starter button for a few seconds noting the display then do the other side.
On a well running bike I'd see around 150V perhaps more. On bikes with failed CDIs I've seen as low as 6v. Often both sides, sometimes one when one side has failed.
You will not get a steady reading! The meter is trying to read pulses, most aren't designed for that so dont worry if it flickers about. Just test long enough to get a good indication/average of the output voltage.
If you don't get voltages well up in the 150VDC range, the CDI has likely failed and the options are:
1. Repair: if you're into electronics and have the patience to dig it out the potting compound.
2. Replacement: But new ones are NLA and a 2nd hand one is a crap shoot.
3. Upgrade: get an Ignitech. There are group buys held every now and then for these ignition controls. Check the [and Buying Forum] .
BTW I don't see why the DC output test couldn't be used to test a suspect Ignitech.
Also, a kill switch leaking to ground will easily shut down an Ignitech as its just monitoring a voltage level on a pin.

And here is a post from Reg about how to troubleshoot a CDI ignition:[edit]
Testing for a lost spark is, or should be, a matter of moments.
Get a meter, lift the seat, open the 2 way connector.
Read the resistance between the blue and white wires and white wire and ground.
Be sure to check the plug that comes from the stator, not the CDI.
The blue-white wires should have 77-95 Ohms.
Check the white-ground which should have 387-487 Ohms.
If that looks ok reconnect the plug open the black/white kill switch connector from CDI to bars and both yellow and pink coil LT ones too.
Set the digital meter to read DC VOLTS on in the 250V range.
clamp black probe to ground. Then test the yellow and pink in turn by sticking the red probe on each as you crank the motor on the button for a few seconds.
There should be >150 VDC flicker on the display with a good CDI box.
I've seen as low as 6VDC on a failed unit.
If it looks ok test again with the kill switch wire connected up and the switch in the Run position.
If you don't get the same results the kill switch is probably shorting to ground.
Cleaning switches [[http://cx500forum.com/mediawiki/index.php?title=Rebuilding_handlebar_switches]]