Alternative (K.I.S.S.) TB Sync Procedure

Adjusting the TB air screws alone does not provide the most effective TB sync because they only compensate for air flow at idle. Most of your riding takes place at higher RPMs. The throttle valves (butter flys) of each throttle body need to be in sync with each other at high RPM.

You should not have to adjust the individual throttle stop screws to achieve this. This assumes that the throttle stop screws have not been grossly misadjusted at the factory (guy on the flow bench had one too many bottles of Sapporo the night before) or the lock nuts have come loose. Here is what I did to get my FJR in sync.

1) Get the engine hot by going for a short ride. When you are at 4200 RPM, squeeze you heals against the frame to feel the level of vibration. This highly precise measurement will be used late to determine how good a sync job you did.

2) Raise Tank and connect sync tool.

3) Turn all four air adjusting screws in until they are lightly seated.

4) Back each screw out 1, turns (per service manual).

5) You may want to place a large fan in front of the radiator to keep things cool (including you).

6) Start engine.

7) The TBs should be out of sync to some extent but not more than 1 to 4 cm of Hg. The actual vacuum level does not matter.

8. Slowly rev the engine up to around 4000 RPM while watching your sync tool. What you are looking for is even vacuum levels as engine speed increases. If you try to do sync the TBs with the engine speed steady (say at 4000 RPM) you will find that the vacuum levels between TB will never be in sync no matter how many adjustments you make. It is more important for vacuum levels to be even during slow, smooth, engine acceleration and not at a steady throttle setting.

9) Using the butter fly sync screw between TBs #3 and #4 adjust the vac level so #3 and #4 are the same when you accelerate the engine as described in step 8, REVING THE ENGINE above. This will take several tries. You may not get them exactly even either, but get them as close as you can (usually within 1 cm of Hg.).

10) Now perform the same procedure on TBs #1 and #2. You may have to rev the engine half a dozen times to get this close.

11) With vacuum levels for TB pairs #1/#2 and #3/#4 matched its time to sync the two pairs of TBs.

12) Rev the engine as described in step 8, REVING THE ENGINE while watching the two pairs of TBs. If they are off by more than 1 cm or Hg., an adjustment is needed.

13) The adjustment screw can only be accessed with the engine off. (The throttle has to be opened about of a turn to get a screw driver on the screw). Turn the screw about 1/8 (either way) of a turn and restart the engine.

14) Check the balance (vacuum level) between the two pairs of TBs. Shut the engine off and readjust as needed. (By now you and your FJRs cooling system will appreciate the large fan you are using, step 5.)

15) When the two pairs of TBs are even (when you smoothly rev the engine) you are finished with this step.

16) Now let the engine idle. Adjust the idle speed to 1000. The tach on the FJR is very accurate. I checked it against a $500 electronic sync tool that counts the vacuum pulses during the intake stroke of cyl #1 and then generates an RPM signal.

17) Now its time (finally) to adjust the air screws on each TB. Use cyl #3 as reference and adjust the other cylinders to the same vacuum level as #3. The actual level does not matter (I know, everyone seems to be hung up on how may cm of HG., but it really doesnt matter as long as idle speed is kept at 1000 RPM.)

18. Make a final idle adjustment (1000 RPM) and you done.

19. Go for a ride and check engine vibration at 4200 RPM, it should be better than when you started. It its worse, you screwed up the adjustment. The amount of improvement really depends on how far out of the sync the TBs were before you started.