- A spark
- Cylinder compression
If your bike won't start it due to one of the above not being present. Before you start troubleshooting, make sure there is gas in the tank by actually looking into it. Also make sure you have the petcock switched to the reserve position if the gas is low.
There are three or four things that need to be done before you can start a Kawasaki Ninja 250
- The ignition has to be turned on
- The kill switch on the right grip has to be in the correct position
- The clutch lever has to be squeezed if you are not in neutral (but you should really be in neutral). Even if you are in neutral, squeezing the clutch lever doesn't hurt.
- The starter button must be pressed
If the bike doesn't turn over when you've done all the required operations, there's an electrical problem, most likely with the battery or one of the switches. Make sure the battery is charged. If it is, make sure no fuses have blown. If they haven't, check to see if you are getting voltage to the starter motor terminals. If you are, the starter motor is likely defective. You should also check the kill switch and starter switches and their connections.
If the bike turns over but won't start you have to check for a spark and make sure gas is getting to the engine.
Make sure there is gas in the tank first! If there is you may need to check the petcock. The Ninja 250 uses a gravity fuel feed by locating the fuel tank higher than the carburetor. The fuel through a vacuum operated valve (The petcock). The valve has two hoses connected to it. One is connected to the carburetor and is for the gas coming out and one goes to the intake manifold which provides a vacuum. If you disconnect the hose from the carburetor, fuel should run out when you crank the engine or you put a vacuum on the vacuum port (be careful to catch the gas if you do this and don't do it with a hot engine). If you don't see gas the petcock may be faulty. You can try applying a vacuum to the control port of the valve and see if the fuel flows. Sucking on the line is one way to do this (but make sure it's the vacuum line, not the gas line if you try this!).
To check for a spark, remove the spark plug from the cylinder. To do this on a Ninja 250 you have to remove the gas tank. I'd heard it said that it is possible to remove a plug without doing this if you use the Kawasaki plug tool, but I'm not sure I believe it!. Hold the tip of the plug against the cylinder head or any other metal part of the frame and crank the engine. You should see a spark across the gap. If you don't, there's probably a problem with the ignition or the plug. Could be a faulty coil or electronic ignition module which will have to be replaced, or it could just be a lose wire. Check with another plug to make sure the one that was in the bike wasn't faulty.
If you are getting a spark and you are getting gas to the carburetor and the engine is turning over on the starter OK, it's possible that the enricher (sometimes referred to as the choke) isn't working properly. Make sure that the cable from the left grip to the carburetor isn't broken and that when you move the choke lever on the grip you can see that the enricher slider on the carb is moving.
It's also possible that there is a problem with the carburetor itself and if so you may need to remove it and clean it out. If the bike has been sitting for a few months with gas in the carburetor, the gas may have evaporated and left a sticky "gum" behind that will prevent the carburetor from working properly and which must be removed. Removing the carburetor from the Ninja 250 isn't the easiest of jobs because it really crammed in there pretty tightly between the engine and the air box. Getting it out is probably more work than cleaning it!
If the enricher is OK, the starter cranks the engine, there's gas, the carb is clean and there's a spark then there may be an engine problem. You need to check the cylinder compression. You need a compression tester to do this. It screws in instead of the spark plug and measures cylinder pressure. When you crank the engine you should see a reading of around 140 psi or more. If it's 100 psi or less there's likely an engine problem (bad valve, bad piston, failed piston rings) which will need the engine taken apart to find.
Probably the most common problems leading to starting problems are a weak or dead battery or carburetor problems due to bad adjustment or build up of gummy deposits. Carburetor problems usually come on slowly though. If the bike is fine one day and refuses to start the next day, I'd first suspect an electrical problem (unless you just filled it with bad gas).
"Bad Gas" is usually wet gas, i.e. gas with water in it. You can also get water in the tank if you leave the bike out in the rain and the gas cap seal is bad. If either of these things happen the water sinks to the bottom of the tank, then when you switch to reserve you suck that water into the carbs and the bike stops running. You can tell if this is your problem by draining the carb float bowls. Each one has a drain port and a screw. Open the screw and gas (or whatever is in the float bowls) will come out of the drain port. If you catch whatever comes out in a glass jar, you will see if there is any water there because it will form a clear layer in the bottom of the jar. You can then clean out your gas tank! If nothing comes out of the float bowls (or just a few drips), it means you have some sort of fuel supply problem (blocked hose, bad petcock etc). Note: if the carb bowls have been drained, it will often take up to 30 seconds of cranking to allow them to fill back up to the point at which the bike will start.
Sometimes changing the plugs can help, even if they seem to be sparking OK. I don't know why this works, but sometimes it just does. So new plugs would come before tearing apart the engine! You may also get a reluctant bike to start better if you jump start it from a car. The car battery has a larger capacity and may be able to spin the starter faster and for longer (though you shouldn't hold the starter button in for more than about 5 seconds on each attempt to avoid overheating it). When jump starting from a car, don't leave the car engine running. The car's electrical system can supply a lot more current then the bike's battery is capable of safely taking.