JOHNDOE83
01-16-2012, 03:52 PM
How to change jetting without a plug chop, taken directly from www.jetsrus.com FAQ section.
The rejetting sequence
The order which provides the best performance is to change:
1) idle,
2) pilot screw
3) slow or pilot jet
4) main jet
5) the needle
6) accelerator pump (if equipped).
7) read the plug.
The process in detail
1) Idle screw: Let engine warm up. Move throttle slightly the response should be smooth. If not smooth then adjust idle about 15% higher than factory recommended stock setting.
2) Pilot screw: (sometimes called a mixture screw) See photo below for typical location of screw. Turn screw in GENTLY until it bottoms. Turn out 1/4 turn at a time (wait 15 seconds between each 1/4 turn adjustment to give engine time to adjust) until highest RPM idle is obtained. Normally do not turn the pilot screw out more than 2.5 turns. If you must turn it out more than 2.5 turns go up to the next larger pilot jet.
If the above adjustments did not get the engine running properly, the jets will need to be changed. How do I get to the jets? Shown below is a typical carburetor. The jets are located in the bottom of the carb. Remove the 4 screws which attach the fuel bowl to the carburetor.
Once the 4 screws are removed the main jet and slow (or pilot) jet can be removed.
3) Pilot jet (Slow jet): If unable to obtain a smooth idle with pilot screw, increase the pilot/slow jet until a smooth idle can be obtained. A larger pilot/slow jet will eliminate or reduce popping that occurs when letting off wide open throttle. The pilot/slow jet will also improve cold weather starts. Go up 1 pilot/slow jet at a time, don't skip sizes. After installing a larger pilot/slow jet, re-adjust the pilot screw. Now take it out and test ride at 1/4 throttle. If the pilot/slow jet is correct it will be easy to maintain a steady speed. Lean symptoms - if the bike surges, carb spits when throttle is opened, exhaust backfires or pops when throttle is closed, or the engine has trouble idling down, engine needs a larger pilot or slow jet to correct. If the engine idles rough, fouls plugs, or is hard to start, pilot is to big, or rich.
4) Main jet: Start with the biggest numbered main jet and run at wide open throttle, the engine should stumble at wide open throttle. Install the next smaller size until the stumble is gone. A general rule is to increase the main jet as long as each jet causes the engine to run as well as or better than the smaller jet in it before. When there is no longer any additional performance gain from the larger jets the jet size is too big - go back down one size.
The rejetting sequence
The order which provides the best performance is to change:
1) idle,
2) pilot screw
3) slow or pilot jet
4) main jet
5) the needle
6) accelerator pump (if equipped).
7) read the plug.
The process in detail
1) Idle screw: Let engine warm up. Move throttle slightly the response should be smooth. If not smooth then adjust idle about 15% higher than factory recommended stock setting.
2) Pilot screw: (sometimes called a mixture screw) See photo below for typical location of screw. Turn screw in GENTLY until it bottoms. Turn out 1/4 turn at a time (wait 15 seconds between each 1/4 turn adjustment to give engine time to adjust) until highest RPM idle is obtained. Normally do not turn the pilot screw out more than 2.5 turns. If you must turn it out more than 2.5 turns go up to the next larger pilot jet.
If the above adjustments did not get the engine running properly, the jets will need to be changed. How do I get to the jets? Shown below is a typical carburetor. The jets are located in the bottom of the carb. Remove the 4 screws which attach the fuel bowl to the carburetor.
Once the 4 screws are removed the main jet and slow (or pilot) jet can be removed.
3) Pilot jet (Slow jet): If unable to obtain a smooth idle with pilot screw, increase the pilot/slow jet until a smooth idle can be obtained. A larger pilot/slow jet will eliminate or reduce popping that occurs when letting off wide open throttle. The pilot/slow jet will also improve cold weather starts. Go up 1 pilot/slow jet at a time, don't skip sizes. After installing a larger pilot/slow jet, re-adjust the pilot screw. Now take it out and test ride at 1/4 throttle. If the pilot/slow jet is correct it will be easy to maintain a steady speed. Lean symptoms - if the bike surges, carb spits when throttle is opened, exhaust backfires or pops when throttle is closed, or the engine has trouble idling down, engine needs a larger pilot or slow jet to correct. If the engine idles rough, fouls plugs, or is hard to start, pilot is to big, or rich.
4) Main jet: Start with the biggest numbered main jet and run at wide open throttle, the engine should stumble at wide open throttle. Install the next smaller size until the stumble is gone. A general rule is to increase the main jet as long as each jet causes the engine to run as well as or better than the smaller jet in it before. When there is no longer any additional performance gain from the larger jets the jet size is too big - go back down one size.