GL1000 Carb Synchronization Procedure

You might consider this item ..synchronization is shown: Randakk’s GL1000 Carb Rebuild Video

Proper carb synchronization is the key to a sweet running bike. When carb sync is out of whack, you can have a poor idle, poor off-idle response, “hanging” throttle and lazy return to idle. You can even suffer from fouled plugs if one or more throttle butterflies are opening early, thereby partially activating the carb’s progression circuitry. Very small adjustments will have a major impact on idle smoothness!

Use a high quality “4-gang” set of gauges to synchronize. It is important that they be accurately matched to each other or your efforts will be wasted. The procedure detailed below is essentially the same for “sticks” or gauges.

Caution: If you choose to use mercury “sticks,” be aware that mercury is an extremely toxic substance. Follow the instructions provided with your synchronization kit to the letter with regard to mercury hazards. If you are not confident in your ability to perform this work accurately and safely, have a professional motorcycle mechanic do this work for you.

1. Imperative – all other tune-up issues must be in order before you synchronize. Note: You should do a valve adjust and compression test (in that order!) before doing ANY ignition or carb tuning. GL1000s will run poorly when valve lash is not set exactly to spec. Fortunately, valve lash stays “in spec” for a long time once properly set. Note: Valve timing on a GL1000 is critical. Verify that your cambelts are installed correctly. The “match marks” on the flywheel and the cam pulleys must align perfectly. The GL1000 is an interference design engine. If your belts are off by 1 tooth, your engine will run like crap. If your belts are off by 2 or more teeth, serious engine damage will occur immediately. Note: Keep in mind that all ignition issues must be perfect before carb work is undertaken. This includes coils, plug wires, plug caps, spark plugs, ballast resistors, breaker points, condenser, ignition advance mechanism, ignition switch, kill switch, main fuse, battery, and all associated wiring harness components. Note: Ignition performance and timing is critical on GL1000s! Ignition problems often mimic carb problems to an untrained ear. Click here for helpful information on setting points and ignition timing properly.
2. Imperative – Your bike must be outside for this procedure to avoid a fire hazard.
3. Be sure you an adequate supply of FRESH FUEL in the tank (at least 2 gallons) so you won’t have to use the “Reserve” setting during initial startup
4. Your bike must be fully warmed up before you begin. A for a 10-15 minute ride around the neighborhood should suffice.
5. The bike should be parked on a level driveway using the centerstand.
6. Place a large fan in front of the bike blowing on “High” toward the bike. This prevents overheating. Also, your goal is to complete this synchronization expeditiously enough so that the bike’s radiator fan does not come on. It’s not a tragedy if it does, but it introduces an unnecessary variable by reducing the idle speed somewhat.
7. Connect the vacuum gauges or mercury “sticks” according to the manufacturers’ instructions. I use a simple set of 4 mercury “sticks” as these are inexpensive and quite accurate. Be very careful handling the “sticks” as mercury is very toxic. Also, make sure you install the flow restrictors into the tubing per the instructions which come with your “sticks.”
8. You will be attaching the 4 hoses to 5 mm brass ports you install into the sides of the intakes after removing the small screws. Hang the sticks from the handlebar so they are secure, vertical and easy to read. You may have to extend 2 of the hoses to reach the far side of the bike. Don’t allow any kinks in the hoses.
9. Mark sure the fuel petcock is turned to “ON.”
10. Start the engine. DO NOT REV THE ENGINE ABOVE 3500 RPMs… THERE IS A DANGER OF SUCKING MERCURY INTO THE ENGINE IF YOU DO. IF THIS HAPPENS, DISCONTINUE THE SYNCHRONIZATION PROCESS AND RIDE THE BIKE FOR ONE MILE OR MORE TO PURGE THE MERCURY FROM THE ENGINE. NO DAMAGE TO THE ENGINE WILL OCCUR IF THIS PURGE PROCEDURE IS FOLLOWED.
11. Adjust idle speed (if necessary) to 1000 RPMs using a curb idle screw.
12. Check gauges or “sticks.” According to the factory specs, all 4 cylinders should be within 50 mm Hg (2 inches Hg) of each other. Actually, a variance of 2 inches is fairly out of whack in my opinion. I aim for a max difference of 1/2″ between the cylinders…1/4″ is better. A low reading means that the cylinder’s throttle plate is too “open.” A high reading means that the cylinder’s throttle plate is too “closed.”
13. If the readings are out of spec, adjust as follows using the 3 sets of adjusters:

Adjuster A – between carb #1 and carb #3 on the right side (balances carb #1 and #3 to each other)

Adjuster B – between carb #2 and carb #4 on the left side (balances carb #2 and #4 to each other)

Adjuster C – the one to the right of carb #4 (left rear carb…this screw balances left pair to right pair). 

14. I use a “combo” tool which allows unlocking of the locknut, adjustment of the balancing screw and re-locking the lock-nut in one step. This tool is available from Motion Pro. It’s almost as easy to use an 8 mm wrench and plain flat screwdriver.