Tuning and Modifications: How to change your carburetor's main jet

1.  Let me first start with the fact that I am NOT a mechanic.  I have been working on motorcycles and scooters for a long time and know a little about what I am doing.  I simply take pictures for other people to use as a guide line to help them modify their own motors.  Any modifications you perform are done completely at your own risk and liability.

2.  Tampering with your motor in any way may void your warranty.  Make sure this is a sacrifice you are willing to make before you begin working on your own vehicle.

3.  Before you begin, make sure you have a nice clean area to work in.  A small amount of dirt can be a big problem when working on the innards of your motor.  Keep your hands, motor, and any other parts you are handling very clean.

4.  This example was performed on a 2003 Aprilia Mojito.  If you own any carbed scooter, the same steps will apply.

5.  ALL bolts and socket head cap screws are in metric! Don't try to work on your vehicle if you don't have metric tools, you will just end up messing up the heads.


Why change your main jet?

Well really you only change your main jet when you need more gas in your motor.  That is if your scooter is running to lean.  There are 2 components to your carburetor in determining how much gas enters your motor.  One is the main jet, and the other is the needle valve.  The needle valve helps you to fine tune and adjust the fuel mixture.  You can use the needle valve to increase and decrease the amount of gas mixing with the air coming into the carburetor.  The main jet is used to change the mixture ratio more drastically than the needle.  If you need to know how to change your needle valve and how to set it click here.

Start by removing everything that is connected to the carburetor. This may or may not include: throttle cable, oil line, gas line, over floe tube, choke, air intake.
Once everything has been disconnected, remove the screws connected to the intake and remove the carburetor.
The carb is going to be filled with gas, so be careful! Lay a paper towel down and flip the carb over. Remove the two screws on the bottom and take off the bottom cover.
Use a clean flat head screw driver to remove the jet. Simply screw in the new larger jet in its place and re-assemble the carb. Bolt the carb back on and re-attach all the cables and hoses. When putting the throttle cable back in there is a channel and a key that has to line up. Turn it until it lines up and falls in all the way.  DO NOT put it in backwards!!!

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