J
Jack Klarich
Guest
S&S Carb Tuning Tips
Idle Circuit
Start engine and run until slightly warm (about 1 to 2 minutes).
Turn RPM adjusting screw to obtain an idle speed of approx. 1000 RPM.
Turn Idle mixture screw clockwise, slowly leaning mixture until engine starts to die. Next, turn screw counterclockwise, slowly richening mixture, until engine RPM start to fall off, counting the number of turns as you do so. Mixture adjustment is correct when screw is positioned about halfway between these points which should be approx. 1/4 to ½ turn out from lean side of adjustment range.
Note:
Turning screw out (counterclockwise) makes idle mixture richer. Turning screw in (clockwise) makes mixture leaner. Normally correctly adjusted screw will be between 1 1/4 – 1 ½ turns out from bottom if intermediate jet size is correct.
After initial idle mixture adjustment is set, reset engine idle to approximately 1000 RPM. A lower idle speed can cause hard starting; poor throttle response erratic idle and unnecessary engine wear.
Once the engine has reached normal operating temperature, repeat steps 3 & 4.
Idle Circuit Notes:
If idle adjustments are made before engine is fully warmed, idle mixture will be rich when engine reaches operating temperature.
Whenever intermediate jet change is made, idle mixture screw must be readjusted.
If idle mixture screw is more than 1 3/4 out after idle mixture is correctly adjusted, it is a fairly good indication that the intermediate jet may be too small and should be changed to the next larger size. Conversely, if the idle mixture screw is less than 1 1/4 turns out the intermediate jet may need to be changed to the next smaller size.
If idle mixture screw is turned completely in engine should not run at idle. If engine continues to run at idle with idle mixture screw seated, recheck initial setting of idle speed screw, and make sure enrichment plunger is seated. If engine still runs at idle with idle mixture screw all the in, contact S&S Tech support.
Accelerator Pump:
The function of the accelerator pump is to improve throttle response when rapidly opening the throttle at low rpm and to aid in cold starts. S&S sets the accelerator pump adjusting screw for maximum volume (all the way out) to aid during initial start-up after installation. Turning the screw inward (clockwise) decreases delivered pump volume. Turning it outward (counter clockwise) increases pump volume.
Adjusting the Accelerator Pump:
Warm engine to operating temperature.
Turn pump travel adjusting screw inward until screw contacts pump actuator arm. This shuts off the pump. Caution – closing adjusting screw with excessive force can cause irreversible damage to screw threads in carb body.
With engine warm and at idle, blip throttle and note throttle response.
Turn pump travel screw outward or counter clockwise about 1/4 turn at a time and recheck throttle response until engine no longer hesitates. This is usually about two turns out.
Minimum pump travel is recommended to conserve fuel, prevent spark plug fouling, and curtail black smoke from pipes when blipping throttle. Black smoke is usually an indication of a rich condition or excessive accelerator pump travel.
Some Performance Notes:
To be sure idle mixture adjustment is correct; always check with fully hot engine.
If popping or backfiring through air cleaner occurs upon taking off, this indicates a lean condition requiring that a larger intermediate jet be installed (one size larger) (size is stamped on bottom of jet).
When fine tuning the intermediate circuit, it is best to turn off the accelerator pump completely. It can mask jetting symptoms.
Whenever the intermediate jet is changed, the idle mixture should be readjusted.
If engine backfires or sputters in carburetor or breaks up and or dies during acceleration, increase or richen main jet size.
If engine runs flat and sluggish or blubbers, or will not take throttle, decrease main jet size.
Always use an insulator block between carb and manifold. If not the heat transfer from the manifold to the carb may cause a temporary rich condition at idle and low speed rpm.
Jetting Chart
1 7/8" Super E
Displacement
55" to 74"
74" to 84"
84" to 98"
Idle Mixture
1 - 1 1/2 turns out
1 – 1 3/4 turns out
1 – 1 3/4 turns out
Intermediate Jet
.0265 - .0295
.031 - .036
.0295 - .033
Main Jet
.062 - .072
.074 - .084
.072 - .082
Jetting Chart
2 1/6" Super G
Displacement
74" to 86"
86" to 93"
96" Up
Idle Mixture
1 1/4 - 1 3/4 turns out
1 1/4 - 1 3/4 turns out
1 1/4 - 1 3/4 turns out
Intermediate Jet
.028 - .031
.0295 - .033
.032 - .036
Main Jet
.066 - .076
.072 - .080
.074 - .088
Note:
If your carb has a serial number that begins with the letter "D" or lower it has a .040 drilled main air bleed. If the serial number begins with the letter "E" or higher it has a .040 replaceable main air bleed.
Note:
Jetting will vary depending on exhaust, cam & compression. Most jetting will be at the smaller end.
Idle Circuit
Start engine and run until slightly warm (about 1 to 2 minutes).
Turn RPM adjusting screw to obtain an idle speed of approx. 1000 RPM.
Turn Idle mixture screw clockwise, slowly leaning mixture until engine starts to die. Next, turn screw counterclockwise, slowly richening mixture, until engine RPM start to fall off, counting the number of turns as you do so. Mixture adjustment is correct when screw is positioned about halfway between these points which should be approx. 1/4 to ½ turn out from lean side of adjustment range.
Note:
Turning screw out (counterclockwise) makes idle mixture richer. Turning screw in (clockwise) makes mixture leaner. Normally correctly adjusted screw will be between 1 1/4 – 1 ½ turns out from bottom if intermediate jet size is correct.
After initial idle mixture adjustment is set, reset engine idle to approximately 1000 RPM. A lower idle speed can cause hard starting; poor throttle response erratic idle and unnecessary engine wear.
Once the engine has reached normal operating temperature, repeat steps 3 & 4.
Idle Circuit Notes:
If idle adjustments are made before engine is fully warmed, idle mixture will be rich when engine reaches operating temperature.
Whenever intermediate jet change is made, idle mixture screw must be readjusted.
If idle mixture screw is more than 1 3/4 out after idle mixture is correctly adjusted, it is a fairly good indication that the intermediate jet may be too small and should be changed to the next larger size. Conversely, if the idle mixture screw is less than 1 1/4 turns out the intermediate jet may need to be changed to the next smaller size.
If idle mixture screw is turned completely in engine should not run at idle. If engine continues to run at idle with idle mixture screw seated, recheck initial setting of idle speed screw, and make sure enrichment plunger is seated. If engine still runs at idle with idle mixture screw all the in, contact S&S Tech support.
Accelerator Pump:
The function of the accelerator pump is to improve throttle response when rapidly opening the throttle at low rpm and to aid in cold starts. S&S sets the accelerator pump adjusting screw for maximum volume (all the way out) to aid during initial start-up after installation. Turning the screw inward (clockwise) decreases delivered pump volume. Turning it outward (counter clockwise) increases pump volume.
Adjusting the Accelerator Pump:
Warm engine to operating temperature.
Turn pump travel adjusting screw inward until screw contacts pump actuator arm. This shuts off the pump. Caution – closing adjusting screw with excessive force can cause irreversible damage to screw threads in carb body.
With engine warm and at idle, blip throttle and note throttle response.
Turn pump travel screw outward or counter clockwise about 1/4 turn at a time and recheck throttle response until engine no longer hesitates. This is usually about two turns out.
Minimum pump travel is recommended to conserve fuel, prevent spark plug fouling, and curtail black smoke from pipes when blipping throttle. Black smoke is usually an indication of a rich condition or excessive accelerator pump travel.
Some Performance Notes:
To be sure idle mixture adjustment is correct; always check with fully hot engine.
If popping or backfiring through air cleaner occurs upon taking off, this indicates a lean condition requiring that a larger intermediate jet be installed (one size larger) (size is stamped on bottom of jet).
When fine tuning the intermediate circuit, it is best to turn off the accelerator pump completely. It can mask jetting symptoms.
Whenever the intermediate jet is changed, the idle mixture should be readjusted.
If engine backfires or sputters in carburetor or breaks up and or dies during acceleration, increase or richen main jet size.
If engine runs flat and sluggish or blubbers, or will not take throttle, decrease main jet size.
Always use an insulator block between carb and manifold. If not the heat transfer from the manifold to the carb may cause a temporary rich condition at idle and low speed rpm.
Jetting Chart
1 7/8" Super E
Displacement
55" to 74"
74" to 84"
84" to 98"
Idle Mixture
1 - 1 1/2 turns out
1 – 1 3/4 turns out
1 – 1 3/4 turns out
Intermediate Jet
.0265 - .0295
.031 - .036
.0295 - .033
Main Jet
.062 - .072
.074 - .084
.072 - .082
Jetting Chart
2 1/6" Super G
Displacement
74" to 86"
86" to 93"
96" Up
Idle Mixture
1 1/4 - 1 3/4 turns out
1 1/4 - 1 3/4 turns out
1 1/4 - 1 3/4 turns out
Intermediate Jet
.028 - .031
.0295 - .033
.032 - .036
Main Jet
.066 - .076
.072 - .080
.074 - .088
Note:
If your carb has a serial number that begins with the letter "D" or lower it has a .040 drilled main air bleed. If the serial number begins with the letter "E" or higher it has a .040 replaceable main air bleed.
Note:
Jetting will vary depending on exhaust, cam & compression. Most jetting will be at the smaller end.
