The proper way to remove the Ninja 250 carburetors

As far as motorcycle carburetors go, the Ninja 250 is one of the most difficult bikes to work on.  Unlike most bikes, the Ninja's carburetors are not easily accessed and are somewhat difficult to remove.

On Youtube, I have seen several videos claiming to have the correct method for removing the Ninja 250's carburetors.  They all seem to disagree and some even resort to using hammers.  To hopefully clear up the confusion, I have produced this video showing how its supposed to be done.  Feel free to watch this and the other videos and decide for yourself which way is better.

I suggest that you watch my video and then print out the following cheat sheet to take into your work area.

Tools Needed:

• 4mm Allen Hex wrench
• 10mm socket and wrench
• #2 phillips or JIS screwdriver
• Pliers
• Old tire or similar to hold tank.

Instructions for removing the carburetors from a bike with the stock unmodified air box.

1. Remove seat.
2. Remove both side fairings (#2 phillips).
3. Remove upper tank fairing bolts (4mm allen).  Note that when reinstalling these bolts, they should only be tightened so they are snug.  Over-tightening will puncture the gas tank. :(
4. Remove the tank overflow hose and the two rear bolts (10mm socket).
5. Disconnect the vacuum and fuel lines from the petcock (pliers).  You should leave the petcock turned to ON as a test.  If its working properly, then nothing more than a few drops of gas should come out.
6. Remove the tank and set it on old tire to keep petcock from touching anything.
7. Remove the bike toolkit and unstrap the battery.
8. Disconnect the battery starting with the negative (-) terminal (#2 phillips).  Make sure you replace the battery terminal bolts because they are easily lost.  Later, when reconnecting, start with the positive (+) terminal.
9. Remove the battery and the rubber holder.
10. Remove the bolts at the bottom of the battery box (10mm socket).
11. Remove the coolant overflow tank bolts and let the tank dangle on the foot peg.
12. Remove the fuse panel bolts and pull the panel away from the frame a little.

If you have previously made the battery box mod to your bike and your battery box is separated from your air box, remove the battery box and skip to step 16.

13. Remove the two upper rear fender bolts just behind the battery box (10mm socket).
14. Remove the two lower fender bolts (10mm socket).  These are difficult to reach and are located just in front of the rear tire under the rear fender.
15. Pull the rear fender backwards as far as it will go.


16. Pull the air box backwards as far as it will go in order to create as large a gap between it and the carburetors as possible.
17. Loosen both front and rear carburetor boot tube clamps on the LEFT SIDE ONLY.  Do not remove the clamps from the boot tubes.
18. Loosen ONLY the rear carburetor boot clamp on the RIGHT side.
19. Remove the screw that holds the throttle cable bracket on and detach the cables.
20. Remove the choke cable.
21. Wiggle the carburetors out of the rear end of the boots.
22. Pull the carburetor out from the left side.  The overflow tube will pull out from the side of the air box.

Re-installation is essentially the reverse of this process.

Secret Ninja 250 Carburetor Passages

Here are the secret passages in the carburetors. They are kind of hard to figure out sometimes and this picture guide shows where they are for cleaning purposes.

When cleaning your Ninja 250 carburetors, all of these passages need to be cleaned so that gas can get through them unobstructed. You can usually do this with spray carburetor cleaner. In some cases, a very thin copper wire can be used for stubborn clogs.

It is recommended that the diaphragms and plastic caps be removed prior to cleaning to prevent damage to the expensive rubber parts.

There are three jets in each carburetor - pilot, main and choke. The choke jet is pressed into the body and does not come out. The main jet is easy to remove with a socket and a large flat head screwdriver. It is actually two parts. The pilot jet is a little more difficult and requires a thin but strong flat head screwdriver.

On both the pilot and the main jet assembly, there are little holes in the ends and sides that must be clear. They are easy to miss sometimes so look carefully to find all of them.  The choke jet can be cleaned with a thin copper wire poked through the end followed by a squirt of carb cleaner.


 Carb Pilot jet Circuit

Carb Main Jet Circuit

Carb Fuel and Overflow Drain

Carb Diaphragm Intake, upper choke and vacuum ports

Carb Choke Circuit

Not pictured is the coasting enrichener circuit. It usually does not need to be cleaned, but because it contains a small diaphragm, you should be careful not to get carburetor cleaner inside it.

Ninja Terminology

Seems like every time someone has a problem with their Ninja they use a totally different language to describe the problem. For example, "It cranks over but it don't turn over" – which is a totally meaningless description. When asking for help online, people need to be precise and technical. So I decided to list out the proper terminology to use when describing problems with the Ninja (not that it ever has any :-) ).

Crank – This is the act of attempting to start the engine in the normal manner. When an engine is cranking, the starter motor is running and spinning the engine. The engine does not have to start in order to crank, but it does have to turn over.

Turn Over - This is when the engine crankshaft rotates. It can either be by cranking, by rotating the crankshaft manually or by other means. The engine does not have to start or crank in order to turn over.

Start – This is when the engine is turned over and begins to run on its own. The method used to turn the engine over is irrelevant. The term "Wont Start" means that the engine will crank normally, but not run.

Bump/Push Start – This is when the engine is turned over by using the wheels rather than the starter motor. Since it is not the normal way to start the engine, it is not the same as cranking. For example, when the engine wont crank, you can push start the bike to get it started.

Run – The engine is turning over under its own power.

Engine – The thing on the bike with a crankshaft and pistons that propels the bike.

Motor – The thing on the engine that cranks it.

Starter – This is the motor.

Solenoid/Starter Solenoid – This is a high amperage relay located on the right side of the bike next to the fuse panel. It has explosed electrical nuts that connect the positive battery terminal to the starter. For testing purposes, these nuts can be shorted to crank the bike.

Break - The act of ruining something.

Brakes - The mechanical devices on the bike that cause it to stop.

I will add more as I come across them.

Downloadable Gaskets for the Ninja 250

The oil screen on the Ninja 250 should be removed and inspected with every oil change.  If there are any metal shavings or particles trapped there, it could mean a big problem.  Steel shavings are the worst.  You can tell them from aluminum shavings because they will stick to a magnet.

Below is a link (click the image) to a PDF file that will allow you to make your own Oil Screen Gasket for your Ninja 250.  I am told this works on all Ninja 250's.  You'll need some gasket paper from the local auto parts store and a printer that will handle thicker paper.  Print out the image full scale on regular paper first.  Once printed, verify the scale by using the scale marks on the image that you have printed.  They should both measure 50mm.  If not, then you may need to adjust your printer settings until you get the scale correct.  Most printers will default to the correct scale. 

Once you are certain the scale is correct, you can print the gasket onto gasket paper.  When done, cut the gasket out using scissors and a hole puncher.  You are ready to replace your oil screen cover.

Depending on the type of gasket paper, a laser printer may work better.  In a pinch, it is possible to use ordinary thick paper.  A cereal box or pizza box usually has some that can be used.

NEW: Here is the Clutch Cover Gasket

 The Clutch Cover Gasket has to be printed out on a wide printer capable of printing on 11"x17" paper.  If you don't have one, you might be able to take your gasket paper to an office supply store that offers printing services.  The actual gasket is only about an inch too big for 8.5"x11" paper.

Ninja 250: Battery Health

Its inevitable that the battery on a motorcycle will eventually fail. But what isn't so obvious is how they fail. A motorcycle battery is a fickle thing. One minute it can be working fine and the next it doesn't have enough power to run the dash lights.

One common failure mode is that the bike will crank just fine, but not start. While a no-start condition can be caused by a multitude of things, a bad battery is one of them. The reason is because the bike's ECU requires a minimum of about 9 volts to operate. Below that, you wont get any spark. When you press the starter button, there can be enough current to crank the engine, but the process of cranking drops the voltage below 9 volts causing the ECU to fail and results in a no spark condition.

Jumping and Charging

The bike can be started by jumping the battery to another vehicle or by using a self contained jump starter device. When using another vehicle, that vehicle's engine should be turned off. The higher voltage of the car (which is charging at 50-100 amps) can damage the diodes in the voltage regulator circuit on the bike.

This is true even when the ignition is off. So when charging the motorcycle battery with anything bigger than a trickle charger, the battery should be disconnected from the bike or the main 30A fuse should be pulled.

Push Starting

Push starting is a bit tricky with a Ninja. Chances are, when you last turned off the bike, you had the transmission in first or neutral. Because the Ninja has a Positive Neutral Finder, you cannot shift it to a higher gear and a higher gear is necessary for push starting.

But before you attempt to push start your bike, make sure that you at least have enough current to run the dash lights. Remember that the ECU needs at least 9 volts. If the dash lights don't come on, then you can push it to the moon and back and still not get it to start.

The first step is to get the bike into a higher gear. You need to get the bike rolling before you can shift to a higher gear. Pull the clutch in and start pushing the bike. After it starts rolling a bit, you can pop it into high gear.

But don't stop. Now that you are rolling in high gear, turn the ignition on and let out the clutch. If its going to start, this will be the time. Be prepared to pull the clutch and apply the brakes as soon as it starts. Remember that you are now in high gear and you need to put it back into first or else when you try to take off, you will stall out again.

Testing the Battery

With a voltmeter you can tell a lot about the condition of your battery. A total of four measurements need to be taken - key off, key on, cranking, and running. The basic procedure is this:
 

1. Turn the key off and measure the battery voltage. It should be higher than 12.5V.
2. Turn the key on - should be higher than 12.1V.
3. Press the starter button and measure while the engine is cranking. It should not go below 9V (preferably not below 10.0V).
4. After the bike starts, measure the running voltage . This should be higher than 13.5V.

In most cases, a bad battery will fail at least one of the above tests.

Battery Size

Depending on your model year, your Ninja takes one of three battery sizes.

The Pregen (1988-2007) takes a 7L-BS battery. It measures approximately 4.5” x 2.8” x 5.2" and has the positive on the right looking at it with the terminals closest to you.

The 2008 Newgen was an odd year and it takes a 7A-BS which measures approximately 5.9” x 3.3” x 3.7” and has the positive on the left.

Other Newgens take a 9-BS battery that measures approximately 6” x 3.5” x 4.25” and also has the positive on the left.

The Pregen can also take a 12A-A battery if you remove the rubber insert in the battery tray. The dimensions of this battery are approximately 5.3" x 3.2" x 6.3" with the positive on the left. The problem is that this battery is only available as a wet battery.

Shorai makes a Lithium version LFX14A2-BS12 that has 14 amps and measures approximately 4.5” x 2.3” x 3.5” with the positive on the left. This is a near drop in replacement for the Newgens. On the Pregens, it requires the rubber battery tray to be removed. Because the battery is smaller than the original, it may require foam padding to make it fit right.

Battery Chemistry

That being said, I am not a fan of lithium (LiFe) batteries. While I have not had any experience specifically with Shorai batteries, I have used other LiFe batteries on my Ninja and they only lasted about a month before they were totally useless. Others have reported similar problems and also problems with the batteries not working at temperatures less than 50F.

But one thing for sure about LiFe batteries is that they are incredibly light for the amount of power they produce. If being lightweight is critically important to you, then a LiFe battery is the way to go.

The most practical battery chemistry these days is AGM. These are far less expensive than the LiFe batteries and usually last longer.

A wet battery is something that brings back bad memories. The electrolyte is literally a liquid acid that can spill out if you tilt the battery. If it gets on your jeans, it will eat a hole in them. If it gets on your skin, it will eat a hole in that too. They used to be the only kind of battery available, but they are generally something to be avoided now.

Every now and then I see a gel cell battery sold for the Ninja. They are usually more expensive and I can't quite seem to figure out what, if any, advantages they have over an AGM battery. The only thing I can think of is that motorcycle AGM batteries usually require the purchaser to add the supplied acid to the battery and charge it before use. Whereas the gel battery comes ready to go. Its not worth the extra expense in my opinion.

Manufacturers

There are lots of battery manufacturers out there. Most of them will work just fine - its just a question of longevity. YUASA is a pretty good one. For better or worse, I ended up getting the lifetime warranty battery at Cycle Gear. Its a junk battery with a good warranty. I've replaced it several times and they always have one in stock and there is no charge for a replacement. If most of your riding is near a Cycle Gear store, then the lifetime warranty battery will do fine, but if you ride very far from the local Cycle Gear you might prefer a better battery like the Yuasa.

Ninja 250: Petcock Problems

The petcock's job is to control the flow of gasoline from the tank to the carburetors. The gas in the tank flows by gravity so even after the engine is turned off, the gas will continue to flow unless something stops it. On motorcycles of yesteryear, the petcock was simply a valve that the rider had to remember to turn off after every ride. On newer bikes like the Ninja, a vacuum diaphragm is used to stop the flow of gas when the engine is not running.

The knob settings on the Pregen (1988-2007) petcock are: OFF, ON, and RESERVE. The OFF setting will shut the flow off completely regardless of the engine running status. There are two intake ports on the Pregen petcock. One is higher than the other. The purpose of this is to provide reserve fuel that is hopefully enough to get to the nearest gas station. The ON selection takes gas from the upper intake. RESERVE takes gas from the lower intake. Both ON and RESERVE require a vacuum from the engine to allow any gas to flow.

The Newgen (2008-2012) has only one pickup at the bottom. The knob settings are: OFF, ON and PRIME. The PRIME selection is a special selection that bypasses the vacuum cutoff and allows gas to free flow regardless of engine run status. PRIME is used to prime the carburetors if they are dry. You should not run the bike when set to PRIME. The ON and OFF selections work the same as the Newgen. There is no RESERVE selection on a Newgen.

Symptoms of a Bad Petcock

The most common symptom is fuel dripping from the carburetors or the crankcase filling up with gas. This is caused when the petcock fails to shut off the gas when the engine is off. This can be caused by several things. The diaphragm o-ring could be bad or the spring that pushes it into its valve seat could be weak. Sometimes the diaphragm itself could be bad allowing gas to leak through the vacuum port and into the carburetor.

A less common failure is when the petcock becomes clogged somehow and the gas wont flow at all or at a reduced rate. This will cause a no-start condition, a poor running condition or a situation where the bike starts fine, but then stalls a few minutes later. The clog can be anywhere from the intake ports to the vacuum port.

The diaphragm itself is a very thin membrane that can tear easily. When it goes bad, gas can be sucked into the vacuum line to the carburetor, or you could also see gas dripping from the petcock body.

In some cases, the rubber gasket under the knob can wear out. When this happens, the knob selections can operate incorrectly such as the ON position drawing gas from the RESERVE intake port or the OFF position allowing the gas to flow.

Caution

If the petcock has allowed gas to run into the crankcase, then you should not run the engine until you have repaired the petcock and changed the oil. Gasoline is a very poor lubricant and your engine could be damaged if you run it that way.

Testing the Petcock

To test the petcock to see if it is operating correctly, you can do the following procedure:

1. Turn petcock to ON (with plenty of fuel in tank).
2. Remove big hose. Gas should NOT come out - except for maybe a few drops that might be in the hose. There should be no continuous drip, but have a glass jar handy to catch any gas just in case.
3. Remove the small hose. There should be absolutely no gas come out of the small hose and port - not even a drop.
4. Attach a 3/16" diameter test hose, about two feet long, to the small petcock port.
5. With your mouth (or syringe if you have one), apply suction to the small tube (again, there should be no gas in the small tube). Gas should flow out of the big tube in a nice thick stream.
6. Stop applying suction. The gas should cut off.
7. For Pregens, switch to RESERVE and repeat the test.
8. The gas that comes out should be free from any debris. If its clear, you can pour it back into the tank.
9. Lastly, switch to OFF and apply suction to the small tube. This time there should be no gas come out.

If the petcock does not operate as described, then you need to remove it and repair it.

Rebuilding

If your petcock is bad, you can either rebuild it or buy a new one. I don't recommend buying used ones because they could be just as bad as the one you are replacing. If you rebuild, be advised that the parts aren't cheap.

There are some rebuild kits out there, but generally, its cheaper to buy just the parts you need from the dealer. Be advised that the Oldgen (1986-1987) used a different diaphragm so rebuild kits for it will not work with the Pregen (1988-2006).

Whatever you do, don't be tempted to use RTV to seal any part of the petcock. RTV is not gasoline resistant and will clog up the works and/or leak.

Finally, if you remove the petcock from the gas tank to rebuild it, be advised that the washers on the bolts that go into the tank are special washers that have been coated with a special gasoline proof rubber. These are sometimes not reusable and should be replaced. If you replace them with hardware store washers, expect them to leak. The main petcock gasket is usually reusable, but occasionally, it has to be replaced as well.

Ninja 250: Overtorquing the rocker arm locknuts

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There have been too many Ninja 250 owners do their own valve adjustments and then end up having to buy a new engine as a result. The problem is that they are overtorquing their rocker arm locknuts.

Here is a photo of a new rocker arm and a worn out rocker arm:

The larger nut on the end is the locknut. To adjust the valves, you have to loosen that and then use a screwdriver to turn the smaller screw inside the nut in and out. Then, to keep the adjustment screw from moving, the locknut is tightened back down.

It is when this locknut is tightened is where some people overtorque it and end up destroying the entire engine.

At first glance, someone might conclude that the worst thing that could happen is that you'd need to buy a new nut or perhaps, at worst, a new rocker arm. But in reality, its more like lighting the fuse to a nuclear bomb.

Overtorquing the rocker arm locknuts starts a chain reaction that ends with the total destruction of your engine.

The first thing that happens is that one of the the little dog ears on the rocker arm is snapped off due to the excessive torque on the locknut. There isn't much too them, and its easy to see how they can break.

 

There should be two dog ears on the rocker - one on both sides. The dog ears are what keep the rocker from coming loose inside the engine. The rockers do not have hinges or retainer pins like they do in some cars so once one of the dog ears breaks off, they are free to come loose.

The next thing that happens is that the loose rocker arm bounces around until it finds its way down the cam chain tunnel. There is really only one place to go at this point - straight into the crank's cam sprocket. What happens is that the loose rocker gets jammed between the chain and the sprocket.

Now when the crank rotates around with the rocker under the chain, it does several things. First, it breaks off a cam chain retainer that is molded into the engine block. Second, it causes the chain to skip several teeth on the sprocket resulting in a major valve timing error.

The Ninja 250 engine is known as an "interference" engine. This means that the valves and pistons take up the same space, but at different times. So as long as the engine valve timing is correct, the piston and valves never hit.

But when the valve timing is off, the pistons will hit the valves with enormous force. This causes several bad things to happen. The most common is that the remaining 7 rocker arms are broken in half.

If you are lucky, then that is the end of the damage. But if not, other things that happen are bent rods, bent valves, broken cam bearing blocks, cracked pistons and cracked engine blocks.

But now, instead of just one rocker wreaking havok in your engine, now you have 14 half rockers doing the same thing. At this time, the engine is not running, but is still spinning - so the little half rockers are going to make their presence known. If any of them get stuck between any gears in the engine, and there are a lot of them, then those gears are toast.

So anyway, I hope this explains why overtorquing the rocker arm locknuts is so bad.