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Carburetor Tuning

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General Jet Needle Changes

 

4) 1/4 TO 3/4 Throttle

The JET NEEDLE is the most effective component in the range. Changing the STRAIGHT DIAMETER (D) will change the calibration in the transition range from the SLOW circuit to the MAIN circuit (1/8 to 1/4) throttle. A smaller diameter will make this range richer and a larger diameter will lean this range. TAPER (A) changes are only made if there is a problem balancing the calibration between 1/4 and 3/4 throttle. If the mixture is rich at 1/4 throttle and lean at 3/4 throttle, a JET NEEDLE with a larger taper is needed. If mixture is lean at 1/4 throttle and rich at 3/4 throttle, change to smaller taper. If the calibration is lean from 1/4 to 3/4 throttle, raise the JET NEEDLE by lowering clip position, or use JET NEEDLE with shorter length (L1). If the calibration is rich, lower the JET NEEDLE with a longer (L1).

5) Wide Open Throttle

Changing the MAIN JET affects this range. Select the size of MAIN JET which offers the best W.O.T. performance, then install one size larger MAIN JET for ideal engine durability.

6) Accelerator Pump (for FCR)

In normal applications, the ACCELERATOR PUMP should not require any adjustment. If a rich stumble occurs as the throttles are opened, the ACCELERATOR PUMP timing can be delayed by widening the gap on the ACCELERATOR PUMP linkage where it makes contact with the plastic lever. Reducing the gap will cause the ACCELERATOR PUMP to deliver fuel earlier.

7) Throttle Valve Cut-Away

(FOR CR, PWK, PJ, & PE) THROTTLE VALVE CUT-AWAY will influence the calibration in the area of 1/8 to 1/4 throttle. What the CUT-AWAY does is change the air velocity over the MAIN NEEDLE JET which changes when the MAIN SYSTEM begins delivering fuel. If the transition is lean change the throttle valve to a valve which has less CUT-AWAY (lower number). If this range is rich use a throttle valve with more valve CUT-AWAY (higher number).

 

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