Quick Jetting Guide.

1. IDLE:  Set idle speed to correct r.p.m. by adjusting the IDLE SPEED SCREW.   Turn The AIR SCREW to achieve the highest idle speed and best response.  After this adjustment has been made adjust the IDLE SPEED again back to the correct r.p.m.

2. OFF IDLE to 1/4 THROTTLE: The SLOW JET and the AIR SCREW are most effective in this range.  When you want a richer mixture use a larger SLOW JET or turn the AIR SCREW in.  The opposite holds true for a leaner Mixture.

3. 1/4 to 3/4 THROTTLE: The JET NEEDLE is the most effective component in this range.  Raising the needle by lowering the clip position at the top of the needle will richen the mixture.  Lowering the needle will lean the mixture.

4. WIDE OPEN THROTTLE (W.O.T.):  Changing the MAIN JET effects this range.  Select the size which offers the best W.O.T. performance, then install one size larger MAIN JET for ideal engine durability.

NOTE: Not all Carbs have AIR SCREWS.  Some have FUEL SCREWS, it is important to differentiate as to which one you have.  This depends on the location of the screw on the carb. (looking at the center of the carb) If the screw is in between the cylinder and the carb body , it's a FUEL SCREW, turn it OUT to get more fuel (richer) if the screw is in between the carb body and the air box, it's an AIR SCREW, turn IN to richen it.  As far as I know this rule of thumb is correct.  Check with your dealer or manual if at all unsure.

Please also check out the following detailed jetting related links:

  • All-Offroads - Overview: Jetting 101
  • Eric Gorr's - Carburetor Tuning
  • Eric Gorr's - CARBURETOR TUNING -  from the book "Motocross and Off-road Motorcycle Performance Handbook"
  • Horizons Unlimited Jetting Page




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