Purpose: Adjust the carbs so all 4 draw the same vacuum. Synchronized carbs increase performance and efficiency.
Overview: Adjust each throttle plate using the synchronizing screws. The throttle plates are linked so the correct order must be followed.
Note: Adjusting the valves will change the vacuum so should be done BEFORE the carbs are synchronized
Clockwise decreases vacuum, counter-clockwise increases vacuum
This is pretty straightforward - you mostly just follow the manual and the instructions that come with your synch tool. A big floor fan blowing on the radiator helps keep the coolant temp down while you're working, or if you have a fanstat bypass switch installed turning it on also helps. If you've had the carbs apart, eyeball the initial balance by lining up the throttle plates with the bypass holes before reinstalling them.
While the Clymer, Haynes and Honda manuals mention no particular order Dave Dodge has one, as follows:
- Sync #3 (right rear) to #1 (left rear).
- Sync #2 (left front)to #1 and #3.
- Then sync #4 (right front)to the other 3.
- Tweek as necessary
Tip (can be used with the alternate synch tool):
For turning the adjustment screw that is blocked by the coolant tube do this:
- Turn off the motor and slightly twist the throttle. This will raise the screw up so you can see to fit the socket on the end of the screw.
- Twist the throttle more to get a straighter shot at it (the socket will go out of sight).
- Now turn the screwdriver the appropriate direction and appropriate number of turns.
- Remove the socket from the adjustment screw, release the throttle and start the bike.
- Look at the gauge and see how you did.
- Repeat 1 through 5 until you get it adjusted correctly. Took me 5-6 times to get that screw adjusted. But it was worth it.
Interceptors have a different firing order: 4,1,2,3 so the carbs must be synched differently.
Adjust the 3 carbs to #4 in this order: #3 to #4, #2 to #4, #1 to #4.