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Pre-Synchronizing Carburetors Print E-mail

Pre-Synchronizing Carburetors

Before reinstalling carbs I "pre-synchronize" by setting the butterflies with a feeler gauge. This gauge can be anything from a store-bought wire feeler gauge to a paperclip. For XS11 carbs I generally use the soft wire from a bread tie.

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The diameter is just right and the soft wire won't scratch the intake surfaces. Exact diameter isn't important.

The idea is to set the opening on all four butterflies so that you can slide the wire under the bottom edge with just a slight bit of friction. By this method you can synchronize the carbs nearly as close as with carb sticks. If you have carb sticks it's still an excellent way to establish a starting point. If you don't have a synchronizer, then this method will set the carbs close enough for good performance.

Sequence is essential for this method, since each carb's adjustment is dependent on the previous one. If you use a different order, say 1-2-3-4, you'll chase around in circles trying to get it right.

Carb sticks use a different sequence. Normally I synch #3 to #4, #1 to #2, then left pair to right pair.

1.  Note, or measure, the approximate gap under the #3 butterfly when you begin. After the "pre-synch" is complete, you'll want to return to this gap to make sure your idle is right when you first start the bike.

 

2.  Start with #3 because it's the has the master adjustment, the big idle adjuster screw. (For reference, #1 is next to the choke lever).

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3.  Using the adjuster screw, open the butterfly unil the wire can slide under the butterfly with a slight friction or drag.

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If you can't open the butterfly enough, you'll have to remove the master adjuster tension spring. Just unscrew the master adjuster all the way and take off the tension spring.

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(Be sure to put the spring somewhere safe so you can replace it when you're finished). This step applies to the master adjuster only, not the balance screws.

 

4.  Adjust #4 for the same feel. This adjustment is with the balance screw between #3 & #4.

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5.  Adjust #2 for the same feel. This adjustment is with the balance screw between #2 and #3.

 

6.  Adjust #1 for the same feel. This adjustment is with the balance screw between #2 & #1.

 

7.  Recheck all four gaps and make fine adjustments as necessary. The closer you get them set here, the less you'll have to adjust when you use the carb sticks. If you don't have carb sticks, this fine adjustment should be close enough for good performance.

 

8.  If you removed the tension spring, be sure to replace it. Return the master adjuster to where it was when you began. This will ensure that the bike will idle when you start it.

 

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