Sunday, October 27, 2013

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.

  1. Remove the two upper rear fender bolts just behind the battery box (10mm socket).
  2. 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.
  3. Pull the rear fender backwards as far as it will go.

  4. 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.
  5. Loosen both front and rear carburetor boot tube clamps on the LEFT SIDE ONLY.  Do not remove the clamps from the boot tubes.
  6. Loosen ONLY the rear carburetor boot clamp on the RIGHT side.
  7. Remove the screw that holds the throttle cable bracket on and detach the cables.
  8. Remove the choke cable.
  9. Wiggle the carburetors out of the rear end of the boots.
  10. 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.