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GL1000 Carb Service-Carb Install and Synchronization Instructions

Please consult a manual before you begin for additional information on carb installation. Do not attempt installing your carbs if you lack mechanical aptitude, proper tools or general intelligence. While I'm on the topic of manuals, I rely on three: the Official Honda GL1000 Workshop Manual, plus the ones from Clymer's and Haynes. Generally, the Honda manual is sufficient, but sometimes the others provide helpful cross-reference.

I strongly recommend that you obtain at least one good manual before you delve into any repairs or maintenance. A good source for the Honda manual is: http://www.helminc.com/helm/homepage.asp

My lawyer asks me to remind you that you are advised to heed all recommended safety practices detailed in the manuals listed above and that you assume ALL risks.

Carb Installation:

  1. Imperative - Move the bike outside before you begin to avoid fire hazard.
  2. Imperative - Disconnect Battery Cables. You should have done this earlier. In case you haven't, to reduce the possibility of creating sparks, disconnect the negative cable first, then the positive cable.
  3. Imperative - Make sure petcock is still in the "OFF" position.
  4. Be sure you have an adequate supply of FRESH FUEL in the tank (at least 2 gallons) so you won't have to use the "Reserve" setting during any of these steps.
  5. Note: I've pre-set idle mixture screws to correct setting. You should not need to adjust.
  6. Detach the air cut-off valve from the carb body. Make sure you loosen the LOWER-MOST screws (I've marked these screws with dabs of yellow paint). There are also 2 UPPER screws that attach the cover to the top of the air cutoff valve…. don't loosen the upper screws! (It houses the diaphragm and spring). Leave the air cutoff valve attached to the rack via the vacuum hose...you only need to gain a fraction of an inch of additional clearance for installation. Make sure the 2 new o-rings on the bottom of the air cutoff valve aren't dislodged (I've secured them in place with Yamabond adhesive).
  7. Loosen the intake manifold clamps on all four intake manifolds (left pair slightly...right pair until loose). Rotate the intakes on the right side 180 degrees to gain additional working space.
  8. Carefully install the entire carb assembly from the left side of the bike. Important: Leave the tape and cardboard attached to the intakes for now.
  9. Reattach the air cutoff valve. Make sure you use the LOWERMOST screws (I've marked these screws with dabs of yellow paint) There are also 2 UPPER screws that attach the cover to the top of the air cutoff valve…. don't loosen the upper screws! (It houses the diaphragm and spring). Make sure the 2 new o-rings on the bottom of the air cutoff valve aren't dislodged (I've secured them in place with Yamabond adhesive).
  10. Rotate the right intakes back into position. Make sure the locating "lugs" fall into position. Don't tighten the clamps yet.
  11. Carefully remove the tape and cardboard covering the intakes. Make sure the 4 new o-rings on the bottom of the intakes aren't dislodged (I've secured them in place with Yamabond adhesive).
  12. Install the 8 acorn head nuts/bolts that attach the intakes to the cylinder head. Loosely install 4 on one side, then do the 4 on the other side. Carefully tighten all 8 acorn head nuts/bolts...do this with a very short wrench 10 mm wrench (I use a 1/4" drive ratchet). DO NOT OVERTIGHTEN - THESE BOLTS WILL EASILY STRIP THE THREADS IN THE SOFT ALUMINUM CYLINDER HEAD!
  13. Retighten all 4 intake clamps.
  14. Attach the new external fuel filter, hoses and clamps between the fuel petcock and fuel pump inlet (rear-most fitting). Note the direction of flow for the filter...arrow points to the fuel pump. Don't overtighten the bracket that secures the filter. I like to put a small additional washer between the contact surfaces to eliminate the possibility of overtightening and damaging the filter.
  15. Reattach the choke cable and throttle cables. Click here for my "Tech Tips" section for helpful information on removing/installing throttle cables..."Knuckle Busting 101 - Throttle Cable Detach / Attach." Make certain you have correctly routed the cables around the frame as they approach the carbs. Refer to the picture or sketch you created earlier.
  16. Readjust the barrel on the "Pull" throttle cable adjuster which is located at the midpoint of the cable. Turn the barrel adjuster "out" to take slack out of the cable...effectively, you are lengthening the outer cable housing to obtain the correct "slack" in the throttle cables. Re-tighten the locknut. Fine-tuning can be done at the second adjuster located at the throttle grip. Proper "slack" is somewhat a matter of personal preference, but there should definitely be some slack or you will have problems getting the bike to settle back to idle speed normally. I aim for about 5 degrees of throttle rotation "slack."
  17. Make sure the plenum to air filter housing rubber gasket is placed in it's correct position.
  18. Carefully, reattach the air filter housing to the plenum using the 2 long bolts with a 10 mm socket on a long extension. Make sure the rubber gasket doesn't move out of position.
  19. Install the new air filter and replace the lid (note direction arrow which points forward).
  20. Reattach the crankcase vent hose to the right rear of the air filter housing. It's easier if you lube the fitting with a smear of light grease.
  21. Reattach the spark plug wires. Position the wires back into the retainer clips on the chrome carb trim stays. Obviously, make sure you get the wires back onto the correct spark plugs.
  22. Remove the golf tee from the fuel line which is attached to the carb body. Using a small funnel (or syringe) add 180cc of fresh gasoline to refill the carb bowls. Don't skip this step...otherwise, you will be grinding on the starter a long time before the engine will start.
  23. Turn fuel petcock to "On" position.
  24. Make sure KILL SWITCH is in "OFF" position and Ignition is still in "OFF" position.
  25. Temporarily, attach an 18" length of fuel hose to the fuel pump outlet (forward-most fitting). Route the end of the hose into a suitable "catch" container.
  26. Reconnect the Battery Cables. To reduce the possibility of creating sparks, connect the positive cable first, then the negative cable.
  27. Turn the ignition switch to "On."
  28. Engage the starter for 10 second bursts followed by 30 second rest periods. What you are trying to do is flush the filter, hoses and fuel pump diaphragm of any debris which might be downstream of the actual filter material.
  29. As soon as a good clear stream of fuel is being pumped by the fuel pump, turn the Ignition to "Off."
  30. Turn the fuel petcock to the "Off" position.
  31. Attach the new fuel line from the carb body (which I provided) to the fuel pump outlet (forward-most fitting). Don't forget the clamp.
  32. Move the bike back inside unless you plan to proceed with start-up and synchronization which is detailed below..

Initial Startup and Carb Synchronization:

Initial Startup

  1. Imperative - Move the bike outside before you begin to avoid fire hazard.
  2. 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
  3. Park on level driveway using centerstand
  4. Turn petcock to "ON."
  5. Turn Kill Switch to "ON."
  6. Turn Ignition to "ON"
  7. Apply Full Choke
  8. Start the bike as you would normally. You will probably have erratic running and sputtering until all the fuel bowls fill completely.
  9. Regulate the choke to maintain 2500-3000 rpms for several minutes. If the engine races above 4000 rpms, shut it off and lower the idle speed. The adjuster is on the the bell crank assembly linkage at the rear of the carbs.
  10. Observe carefully for any fuel leaks and rectify immediately as necessary.
  11. Gradually push the choke knob all the way in as soon as you are able.
  12. The idle speed will have to be reset now (it's probably too high). Aim for about 1000 rpms.
  13. Go for a 10 minute ride around the neighborhood.
  14. Return and park outside on level driveway (on the centerstand).
  15. Check again for any fuel leaks.

Carb Synchronization:

  1. Imperative - all other tune-up issues must be in order before you synchronize. Especially: plugs, plug wires, points and timing! Click here for my "Tech Tips" section for helpful information on setting points and ignition timing properly.
  2. Imperative - Your bike must be outside for this procedure to avoid 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 (see above).
  5. 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 recommend a simple set of 4 mercury "sticks" as these are inexpensive an inherently more accurate than vacuum gauges. 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 5mm 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 RUN 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.
  12. Check gauges or "sticks." Acording 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 inch between the cylinders. A low reading means that cylinder's throttle plate is too "open." A high reading means that cylinder's throttle plate is too "closed."
  13. If the readings are out of spec, adjust as follows: There are 3 sets of adjusters:
    1. Adjuster A - between carb #1 and carb #3 on the right side (balances carb #1 and #3 to each other).
    2. Adjuster B - between carb #2 and carb #4 on the left side (balances carb #2 and #4 to each other).
    3. Adjuster C - the one to the right of carb #4 (left rear carb...this screw balances left pair to right pair).
  14. Note: 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 a long screwdriver.
  15. Loosen the locknut at Adjuster A. Turn the screw to balance carb #1 and carb #3 on the right side. Adjustment is correct when both cylinders show approximately the same reading. Carefully, tighten the locknut while holding the screw stationary. Re-check readings on gauges or "sticks." Repeat as necessary if the readings have drifted.
  16. Loosen the locknut at Adjuster B . Turn the screw to balance carb #2 and carb #4 on the left side. Adjustment is correct when both cylinders show approximately the same reading. Carefully, tighten the locknut while holding the screw stationary. Recheck readings on gauges or "sticks." Repeat as necessary if the readings have drifted.
  17. Loosen the locknut at Adjuster C . Turn the screw to balance left carb pair with right carb pair. Adjustment is correct when both pairs show approximately the same reading. Carefully, tighten the locknut while holding the screw stationary. Recheck readings on gauges or "sticks." All 4 cylinders should now show the same reading. Repeat as necessary if the readings have drifted.
  18. Note: Don't get too anal here. Perfection is not possible. I strive for a tolerance of 1/2 inch Hg between all 4 cylinders. You can "chase" this all day and not get much closer due to the inherent "slop" in the linkage design.
  19. Check idle speed and re-adjust if necessary to 1000 rpms.
  20. I like to do one additional check - SLOWLY raise the engine speed to 3000 rpms and observe the gauge readings. The readings should still be closely grouped. If not, you may have carb, ignition, compression or vacuum problems. Mis-matched main jets or jet needles can cause this problem. Other causes are dirty air filters, worn carburetor bodies or throttle slides and restrictions in the exhaust system. Can also be simple mechanical problems ("slop") with the linkage. In any case, if the readings fall badly out of spec at 3000 rpms but are good at idle, you may wish to investigate the cause. Some folks recommend synchronizing at 3000 rpms for better cruise performance but I do not. It's hard to live with a poor idle!
  21. Remove the gauges or "sticks." Replace the small screws in the intakes which were removed in step #8.
  22. Road Test.
  23. Recheck for leaks.
  24. Miller Time!

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