 |
|
|
|
There are 7 unlogged users and 0 registered users online.
You are an anonymous user. You can register for free by clicking here
|
|
|
|
|
|
|
Carburetor fuel circuits and functions:
1) Pilot jet/slow jet - Affects mixture from idle to 1/3 throttle opening. The pilot jet meters fuel to the "bottom end circuits"
2) Air screw - Meters air to pilot jet. It is usually located near the back or air box side of the carb. Turning in clockwise, will richen the pilot mixture. Turning out, counter clockwise, will lean out the pilot mixture. Average setting for most 2 strokes is 1 to 2 1/2 turns out. Refer to owner's manual.
Note: If the adjustment screw is in the front of the carb, it is a fuel screw and not an air screw; it is adjusted the opposite of the air screw. Most 4-strokes are this way.
3) Jet needle aka Needle - Affects the mixture from 1/4 throttle to full throttle. The needle is in the leanest position when the clip is on the top, and richest on the bottom. The needle calibrates the full to the change in throttle valve (slide) opening. The further down the needle is, the later the main jet comes on and the leaner the mixture at that point.
4) Main Jet - This circuit affects the mixture from 1/2 throttle to full throttle. This is your full blast top end circuit. This circuit is most accurately tuned by checking the plug for the correct color, sort of mocha brown.
5) Float/Float valve/Float level - Your owner's manual has the correct level and procedure for calibrating your bike. Here are some symptoms that would indicate the need for float adjustment.
A) If float level is too high, the float bowl overflows out the drain hoses, and fuel often blocks the air passages that allow the carb to de-pressurize. This causes a bog, or hiccup over large hits.
B) If float level is too low, the engine starves for fuel off idle, causing a "boooooowang" sound very similar to a pilot jet or air screw set too lean.
Jetting Guidelines; Eliminating the variables.
1) Never change more than one circuit at a time. You need this tool to tell you exactly which circuit is affecting performance and at what throttle opening.
2) Use fresh gas. Octane ratings diminish with time and the higher the octane the slower the burn and richer the mixture. The quality of today’s pump gas is decreasing. To compensate for the fuel, richer jets are required. Also note that fuel with ethanol (aka MTBE) also requires a slightly richer mixture.
3) Always start with a fresh air filter. Let a freshly oiled air filter dry at least 6 hours in advance so that the alcohol in the air filter can evaporate. Then match the carb to a motor that breathes properly. Otherwise, the engine will run slightly leaner when the clean air filter is installed.
4) When performing a plug check, use a good used spark plug. New plugs are white and are hard to read accurately for mixture checks. If you have to use a new plug be sure to put at least 15 to 20 hard minutes on it before attempting to get a reading.
5) Always check for clogged carb vent lines. Clogged lines will cause hard starting and bogging when the motor is hot. They can also cause erratic running that seems to mimic a mis-adjusted float, but worse. Performance will seem rich and acceleration will be sluggish off idle.
6) If you’re trying to track down a jetting problem, don’t change your premix oil brand or the ratio. The pre-mix ratio will determine how much fuel is available to be burned because the oil isn’t burned, and in terms of liquid volume, the oil takes up a portion of the liquid (oil + fuel). While the ratio will have a minimal impact when making small changes, remember that you’re trying to eliminate variables.
How to Jet
1) Mark your throttle housing and grip in 1/4 turn increments. Use a marker, razor blade, etc.
2) Now get the motor to operating temperature by riding around, away from the pits.
3) Once the motor is warm, ride in 2nd and 3rd gear from the low RPM to high RPM. This puts a good load on the motor and is an accurate test of performance.
Note: try to notice if the problem gets worse or better as the motor heats up.
4) Now try to locate the throttle opening at which the problem exists. See table below.
|
|
|
| Overview: Jetting 101 | Log-in or register a new user account | 0 Comments |
|
| Comments are statements made by the person that posted them.
They do not necessarily represent the opinions of the site editor. |
|
